IFATCA The Controller - Winter 1961/1962

LuflstraBenuberwachung mit GRS Unsichtbare Faden fiihren die Flugzeuge vom Start zur Landung. 3 GroO-RundsichtRadaranlagen, auf dem Deister bei Hannover, auf der Neunkirchner Hiihe im Odenwald und in MOnchen-Riem tasten den Himmel ah und vermitteln den Kon takt von Bord zu Boden. Mit einer Reichweite von 220 km, einer Hiihenerfa ssung von 16 km Oberwacht man so den gesamten Luftraum Ober Westdeutschland. Die Schirmbilder warden vom Aufstellungsort der Rodaranlag e zur Zentral e im Flug hafen Ober Richtfunk verm ittelt. Der stete Uberblick Ober dos Geschehen gibt Sicherheit im Luftverkehr.

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From the coracles of prehistoric times to the jet airliners of to-day, fast efficient transport has been the key to the progress of civilization.

But with each major improvement, the associated problems of operating each form of transport have grown in complexity, and now demand as much attention as the improvement of the land, sea or air vehicles themselves.

In the case of aviation, more airlines, faster aircraft, bigger airports - all combine to compel those in charge of air traffic to cry out for modern, fast data processing equipment. SATCO automatic air traffic control is a practical solution to their problems.

EFFICIENT TRANSPORT MEANS PROSPERITY

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SAYCO SIGNAAL AUTOMATIC AIR TRAFFIC CONTROL Satco comprises the ground equipment to predict, coordinate, check and display the movements of air traffic en route and In terminal areas. It provides an extremely rapid method of calculating flight paths, tor assessing potential conflicts and for coordination between Area Control Centres. Special features are Included for military I civil coordination and for the control of jet-powered traffic.

The system has been ordered by The Netherlands Government and the first phase Is now on operational test

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N.V. HOLLANDSE SIGNAALAPPARATEN • H EN GELO - NETHERLANDS

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DAS GENAUESTE ANPASSUNGSFAHIGSTE UNO UMFASSENDSTE NAVIGATIONSSYSTEM FUR DAS DUSENZEITALTER THE DECCA NAVIGATOR

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IFATCA JOURNAL OF AIR TRAFFIC CONTROL

THE CONTROLLER Volume l 路 No. l

Frankfurt am Main, Winter 1961/62

Publisher: International Federation of Air Traffic Controllers' Associations, Cologne-Wahn Airport, Germany.

CONTENTS

Editor: Walter H. Endlich, 6 Frankfurt am Main l, Raimundstrasse 147, Phone 521710.

Editorial

Production and Advertising Sales Office: W. Kramer & Co., 6 Frankfurt am Main NO 14, Bornheimer Landwehr57a Phone 44325, Postscheckkonto Frankfurt am Main 11727'.

Rate Card Nr. l.

Printed by: W.Kramcr& Co., 6 Frankfurt am Main NO 14 Bornheimer Landwehr 570. '

Contributors ore expressing their personal points of view and opinions, which must not necessarily coincide with those of the International Federation of Air Traffic Controllers' Associations (IFATCA).

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Walter Endlich

The Philosophy behind and some Details of the Apollo Computer System

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H. S. Bray On the Automation of the Air Traffic Control Services in the German Federal Republic

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Roland Maier

First Civil Secondary Radar for Continental Europe

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IFATCA does .n?t assume responsibility for statements made. a.n~ opinions .ex~ressed, it does only accept respons1bil1ty for publ1sh1ng these contributions.

Flight Plans and Flight Programmes

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Contributions are welcome as are comments and criticism. No payment can be made for manuscripts submitted for pub.lication in "The Controller". The Editor reser~es the .right to ~ake any editorial changes in manuscripts, "':'h1ch he .believes will improve the material without altering the intended meaning.

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Written permission by the Editor is necessary for reprinting any part of this Journal.

J.E. D. Williams

The lnstitut du Transport Aerien

ACCESS, Down to Earth I Ground Communications

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Jesse Sperling

ICAO Communications Division completes work

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Flarescan

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Beacon: 5-year ATC Plan

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Phil Geraci

The Importance of the so-called "Human-Factor" for the Reliability of Collision Prevention in the Terminal Area

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Prof. Dr. H. von Diringshofen Advertis.ers in this Issue: The Decca Navigator Company (3). Gilfillan Bros. (13). General Precision, Inc. (Inside back cover). Marconi's Wireless Telegraph Company (Back cover). NV. Hollondse Signaolapporaten (2).

Telefunken (Inside front cover).

Picture Credit: British Features (7) Damning (5) GPL (21. 22. 23) Hrizeltinc Corp. (33). Maier (14:1 Marconi Aeronautical (34). Osmun (25) Ryon Electronics (36) Tews Instruments (34)

IFATCA Annual Conference

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Great Problems in Air Traffic Control

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Survey: Modern Equipment, Installations and Systems for Air Traffic Control and Air Navigation

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Editorial

This then is the first issue of IFATCA's Journal of Air Traffic Control. Unfortunately it appears somewhat behind schedule, the technical and administrative changes from "Der Flugleiter" to "The Controller" caused more work than we had expected. All readers are kindly requested to accept our apologies. We try to do better in future.

The Journal serves an important purpose. It is the voice of the majority of the European air traffic control personnel. One day, if IFATCA continues progressing as it does presently, "The Controller" may very well represent the Journal of ATC associations all over the world.

Before outlining our editorial policy, it may be worthwhile to reiterate how IFATCA came into being. Some ten, twelve years ago, when traffic increased and the significance of air traffic control was widely recognized (yet not always readily accepted by the authorities which had to provide for the funds), the first air traffic controllers associations were founded. Others followed, and already in these days a frank and immediate exchange of opinion on professiona I matters among controllers created the feeling of belonging together and working jointly in a highly specialized field for an attractive goal: Aviation Safety.

Experience flights to adjacent airports and ATC unitsunfortunately very few were granted - helped to understand the fellow controllers problems as well as those of the pilots. Although extensive correspondance was exchanged between the various ATC associations, the activities were not coordinated but progressed at random.

On a national level some associations established contocts with other parties interested in air traffic control: Pilots, airline companies, flying clubs, industry, etc. Internationally. however, no possibility existed where controllers could discuss matters of professional interest directly among each other or with any of the parties concerned.

Therefore 1 the idea of an international ATC federation, once brough t up, was enthusiastically responded to. In November 1959, delegates of fourteen European nations met in Frnnkfurt, Germany, and, after careful study of the subject, declared their intention 10 found an international federal ion of air traffic controllers associations. A working group 1.vas established and was charged to draft Conven1ion, Constitution, and By-Laws. The Netherlands Guild of Air Traffic Control Officers prepared the Constitutional Confe;·ence, which took place in Amsterdam, October 1961.

Just a few months have passed since then. Member P.ssoc1citions os well as the Elective Officers of the Federal ion were ciuite occupied with administrative matters and could not d~vote much time to the investigation of professional problems.

Nevertheless, the few initial communications IFATCA so for had with oviation organ 1zations and industry, already 1nclirnte the potential value of the Federation in iern1~ of exchonging expert opinion and disseminoting 1nfornwt1on to those who are immediately concerned.

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Walter Endlich

Here is where "The Controller" comes in. This Journal is intended to be a platform for the discussion of technical and procedural developments in the field of air traffic control.

Although ATC, unfortunately, is not a matter of general interest we hope to satisfy a great variety of readers: Cont r o 11 er s, we like to keep informed about all activities in their profession.

Civil and military aviation authorities may appreciate a direct opinion of the people in the field.

The same applies for i n tern at ion a I a via t i 0 n organizations. They usually obtain a great deal ot information through their members and from international conferences. The viewpoint of the qualified controller, based on his practical experience, can very effectively supplement this information and contribute to complete the overall picture.

Industry is welcome to report in this Journal abo t their research and development activities, because it is thue controller who has to work with their equipment later He is in _a position to re~der valuable advice, which sho~I~ be r.ead.dy accepted, a~ industry is usually obtaining infor'.'1at1on tn terms of equ1p~ent specifications instead of being told about the operational requirements.

P i I o t s, a i r I i n e s ta ff p e r so n n e I , and ex _ e c u _t iv e a i r craft operators may be interested to discuss procedures and operating practices with the people to whom they trust their aircraft and their passengers. . A i r po rt a d m i n .is. t r a to r s are probably more interested to get an op1n1on on approach lights, runway acceptance rate, automatic landing, and related sub· t which shall be adequately dealt with in "The Contro\~:r'~' The h u m a n e n g i n e e r i n g e x p e r t s , we h · .

• • • • ope, w1 11 :ontinue 1nvest1gah~g the environmental factors in air traffic control. There will always be ample space · .

1n our Journal to inform the aviation public about the results of their studies which contribute to improve working conditions and have such a decisive bearing on safeiy in air navigation.

To make the Journal as interesting and as informati .

Ve as poss1"bi e, we so I"1c1t our readers cooperation. Contributions are welcome, as are comments and criticism.

There is an IFATCA representative in almost any European country, who will also be the national distribution agent for "The Controller". Subscription orders should be directed to him, whilst contributions are kindly requested to be sent to the editor. Any enquiries regarding advertisin and management will be dealt with by W. Kramer & C g

A list c~mprisi_ng all nan_ies an_d addresses of I FAT(~ representatives will be published in the next issue of our Journal.

Because of technical reasons the German 1 ·nlay "D er Flugle!ter" is included in all copies of this issue.

H. S. Bray

The Philosophy behind and some Details of the Apollo Computer System at the Prestwick Oceanic Air Traffic Control Centre* 1. Introduction The Ministry of Aviation have been studying the possible uses of digital computers for improving air traffic control for several years. Ferranti Ltd. first submitted proposals to the Ministry for such equipment in ·1954. At that time thoughts were directed towards a digital store with fairly comprehensive communication channels via teleprinter links. The machine was to have consisted of a magnetic drum with control logic and a rudimentary arithmetic unit.

A contract for a machine of this type was placed in 1957 and most of the design work was completed, using techniques identical to those in the Ferranti Pegasus computer.

However, as the Ministry's studies continued it became evident that a fairly fast data-processing computer would be needed suitable initially for a variety of control functions, and which could form the nucleus of a steadily developing experimental system. This led to the design of the Apollo computer system.

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by asking controllers what their difficulties are, but the controllers themselves would be the first to admit that definition is not easy. There are a lot of factors involved, and a considerable amount of analysis of the data resulting from these factors is required before much progress can be made. Furthermore the relevant data is not easy to extract from the enormous number of messages transmitted in the exercise of control. This is where an experimental computer can make its first major contribution.

Computers work at a very high speed compared with human beings, and can be programmed to do all the necessary statistical analysis, and produce the required results before the conditions have changed so much as to make the conclusions useless, or at least less valuable.

The second way in which an experimental system can help to define the problem is to use it in a quasi-operational role in conjunction with controllers working at flight progress boards. This will help to show up deficiencies in the methods currently in use, and lead to decisions on how

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A decision to install automatic data-processing equipment to help controllers to continue to do their work efficiently despite the rapid increase of airline traffic must be backed by sound and comprehensive knowledge of what the control problem is and of just what computers can do.

The best way to obtain this knowledge is to experiment.

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ATC Symposium, Stockholm, December 1960. Reprint with kind permission of Royal Boord of Civil Aviation.

. re 1·1ev 1·n g controllers . of muc h use the computer can be 1n .

I . · · · Tlie next step ' leading rou t ine manua processing act1v1t1es. . directly from this, is to use the computer sy~t_em_ for periods of active control. This will produce valuable 1nformat1on, and will not be dangerous in any way prnvided the corn· puter's activities are monitored by the existing operat1oncil controllers, who would thus be fully awore of the traffic situation and would be reedy to take over in the evenr of failure.

Experiments will also show whether the help given to controllers by the reduction of routine activities does not at the same time make their lives more difficult. For example, communication with the computer must be by keyboard rather than voice or paper and pencil. Furthermore it may prove more difficult for a controller to assimilate a traffic situation when he is less directly concerned with extracting the data he uses on his flight progress board.

On the other hand the filtering of data through the computer so that he is presented only with relevant information should leave him more time for studying the situation end making decisions.

It should also be possible as the result of experiments to decide on the best form of data transmission channels between controllers and pilots. It would be desirable ultimately to have direct inputs to and outputs from the computer, and this raises questions on data links, amount of redundancy required, and speed of communication.

Simulation experiments will give some idea of the effect on control efficiency of greatly increased traffic flow, the interaction of supersonic and very slow aircraft, and other foreseeable future conditions. The effects of using smaller separation standards can also be studied, perhaps in conjunction with more detailed methods of conflict calculations, using weather information and aircraft characteristics, for example, which would take controllers too long to do by hand.

There are many other aspects of air traffic control which can be studied, but of equal importance are studies of the capabilities of the computer system. One of the most pressing problems is that of reliability, and what can be done in an operational computer system in the event of failure. Other problems include the specification of the type and capacity of storage, types of input/output device and display equipment, and speed of operation.

The Ministry of Aviation are studying the work done in the United States and in Europe and have been in close contact with related defence work being done in the United Kingdom. The experimental equipment to be installed at Prestwick to study area control over the North Atlantic will be supplemented by further equipment to study the problems of airways control in the south of England.

From these studies and experiments they hope to learn "what are the most suitable procedures for a semi-automatic control system; what the initial distribution of work should be between controllers and computer, and how the data-processing system should best be organised to provide adequate reliability at economic cost, and yet be capable of expansion to meet the future demands" {Ref. 1).

2. The Oceanic Area Experimental System 2.1. Background To give some perspective t~ the description ?f the experimental system, the following paragraphs give a very brief account of the procedural method of control at present in use. It is worth mentioning here that although the 1'-lorth Atlantic Oceon covers a vast area there is a control problem even with current peak tr?ffic densities. The lack of odequate navigational aids wh1.ch enforces the use of lorge separation standards in the interests of safety, and the exigencies of the weather and the demands of the airline operators with regard to running costs and passenger scitisfoction, result in a concentra_tion of aircraft in a norrow band of routes within o period of a few hours.

One of the uses of the experimental system will be to develop techniques for coping with the rapidly increasing traffic densities.

Control of transatlantic traffic is exercised by three air lraffic control centres - at Gander in Newfoundland and at Prestwick and Shannon on this side of the Atlantic. The area controlled by Gander extends eastwards to 30° W, and the Prestwick/Shannon area covers roughly 10° W to 40° W and 43° N to 61° N. The overlap between 30° W and 40° W facilitates transfer of aircraft from one control area to the other. Although Prestwick and Shannon both have control over the same area, the information displayed on lhe flight progress boards is the same at both centres, and there is normally no confusion over which aircraft are be;ng controlled by each control centre it depends mainly on which centre the flight plan is directed to. There is close collaboration between the three centres by direct telephone links.

At Prestwick the basis of control, as at other centres, is the flight progress strip. There are four strips for each aircraft. Each of these strips refers to one of the four reporting meridians in the control area, 10°, 20°, 30° and 40° W. During busy periods five flight progress boards are used, with two controllers for eastbound, two for westbound, and one for high level traffic (above 29 OOO ft.).

There is also a pre-flight planning position, using flight plan information, which ensures adequate separation of aircraft as they enter the control area.

The flight progress strips are written out by hand and contain estimates of time height and latitude at the reporting meridians, derived from flight plan plus A.T.D .. or departure plan. As an aircraft crosses the area its pilot transmits a position report after crossing each meridian and gives a revised estimate for the next meridian. Controllers use this information to up-date their strips, and their control function consists essentially of observing the displayed information to observe potential conflicts between aircraft flight paths and issuing reclearances when necessary. The separation standards at present in use are 30 minutes flight time longitudinally, 120 nautical miles laterally and 1000 ft. vertically except for aircraft above 29 OOO ft. which must have 2000 ft. vertical separation.

Communication of data to and from the control centre is by several types of channel. Data from airports, consisting of flight and departure plans, A.T.D's and amendments, arrives by telephone or teleprinter. Data from aircraft in flight is transmitted by VHF/RT and relayed from receiving radio stations by teleprinter; these channels are used for position reports, departure plans (sometimes) and reclearances. Communication with the other co itrol centres, Gander and Shannon, is by telephone.

2.2. Purpose of Experiments An extensive programme of experimental work is bei~g planned, and the following broad objectives are listed in the operational requirement. a) Investigation of methods of using automatic equipment to relieve controllers of routine manual data-processing task. b) Standardisation of data transmitted to the control centre to reduce the need for manual processing prior to input to the automatic equipment. c) Collection and statistical analysis of data for research into methods of increasing air space utilisation.

d) Development of optimum division of functions between controllers and between contro llers and automatic equipment, by direct measurement of efficiency under quasi-operational conditions initially, and fu lly operational conditions ultimately. e) Determination of the requi rements for different types of output and d isplay equipments. f) Development of new control procedures for the North Atlantic.

2.3. The Experimental System Since there are plans for ultimately using the experimental system in an operational role, it must have all the essential features of the ex isting procedural system. The layout of equipment in an extension to the control room and the accommodation for the computer are shown i~ Fig. l, and a block schematic of the equipment in Fig. 2.

A set of four flight progress boards is provided for the experimental controllers, who receive ond transmit all their information via the computer. For each controller there is a two-way link with th e computer in the form of o page printer and a functiona l keyboard. Two page printers are provided to produce flight progress strips, which are i nserted into holders and given to the appropriate controller by assistants. The only other source of information for the controller is o set of cathode ray tube displays, mounted above the fli ght progress boards, w hich are capable of displaying short alpha-num eric messages or data in pictoria l form.

All the data relative to control which is not generated by th e exp erimental co ntroll ers is fed into the computer by teleprinter keyboard operators in th e inpu t room . This room also contains page printers and other facilities which duplicate all the messa ges rece ived by the operational cont ro ~l ers. In one woy of using th e sys tem t hese messages are edited by a controller who th en gives th e appro p riate operator the details o f the essential data to be f ed i nto the computer. In another type of experiment the operators would feed in data d erived from simu lated traffi c situations to tes t th e effect on th e system's efficiency of condi tions w hi ch would saturate the prese nt control syste m such as high d ensity or redu ced separation sta ndards. ' The important thing to note is that all data used by the contro llers is fed to them via th e compu ter, w hich is capable of processing the data so that it appea rs before the controllers in its most suitable form. Furth ermore the controllers are p rovided only w ith the data th ey rea lly need, and are relieved of th e t ime co nsuming task of unravellin g garbl ed messages and d iscarding redund a nt information.

A ssociated with th e computer are input and output devices for use by the programmers. They include two tape read ers for the input o f programmes and suppl ementary data used by the programmes. (Such dote might for ex amp le be meteor o logica l information ), a page printer for th e programmers' use in developing new programmes, a nd two tape pun ches for the output of traffic records and statis tica l o r o th er data wh ich requires f urther computation or tabulation. .The system is designed to be fl exib le in order to cope with the grea ter d eman ds that w il l be mode o n it as the scope of th e experiments enlarges. Details of how thi s has been do~e wil.I be ~iven in Section 3, but briefly the f ea tu res which give this fl exibi lity are the high speed and

comprehensive instruction code; the " interrupt" facility which permits the add itio n o f further input and outp ut devices of various types w ithout imposing restrictions on the operation of those already connected; the ease of changing stored programmes ; and provision for a fourfold increase in the immediate access storage capacity for programme and da ta without major mod ification to the computer.

2.4. The Experimental O rganisation The conduct o f the expe rimen tal work w ill be the responsibil i ty of the Ministry o f Aviation's Air Traffic Control Experimental Unit. Under the d irection o f a project lead er th ere w ill be a team of pr ogrammers consisting of an experienced A ir Traffic Contr o l Officer, on Operations Officer a nd a Statistican. There w i ll also be an operating team comprising four Air Traffic Con tro l Officers, two Operati o ns Officers, four Air Traffic Contro l Assistants and four Telepri nter Opera tors. Assistance in the writing of the operational programmes for the initi al experiments is being given by the M a th ematica l Services Division of th e Roya l Aircra f t Establishment, until the A.T.C.E.U . p rogrammers are fully tra ined.

3. The Apollo Computer and Peripheral Equipment 3.1 . Design and Development Th e design of the computer and its peripheral equipment has been influenced by the fol lowing considerations: a) Th e need for simu ltaneous ope ratio n o f the input and output d evices. b) Possible demands for increased storage capac ity after th e equipm ent has been manufactured a nd insta ll ed. c) Flexibili ty to ensure that new and modified experiments con be conducted without modification of the computer. d) Hi g h computi ng speed for the same r ea son as in c). e) Proposed use of the equipment for the co ll ecti o n and statistica l ana lysis of air traffic control dote . f) The desire for a facility to perform computat ions of secondary importa nce during periods when the programme s relating to control are held up pending the arriva l of new data. g) The possibi lity that an operationa l system wi ll ulti mately be r equired which can be developed from the experimental system w i th the m inimum of redesi gn.

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Study of these factors and the detailed operational specification led to the design of what is in effect a highspeed general purpose computer embodying a special "interrupt" facility which permits communication with a large number of peripheral devices in such a way that there are virtually no time restrictions on their operation, and they can be connected directly to the computer without the need for complicated and expensive buffer storage or signal converter units.

Flexibility and ease of expans:on are provided by the high speed, the ease of changing stored programmes, the lack of restrictions on the peripheral equipment, and provision for increase of programme and data storage. The system is designed to handle up to 100 aircraft in the early experiments, the limit initially being imposed by storage capacity. The computing speed is sufficiently high to cope with five times this volume of traffic and the associated analytical computations.

The detailed design work, based on well tried logical circuits was started in May 1959. Manufacture and functional testing of all the components of the system was completed by the end of 1960. Then followed some months of programme testing, and after Acceptance Tests the system was installed at Prestwick and the experiments are row in progress.

3.2. The Apollo Computer 3.2.1. General Description

The Computer is a fully transistorised parallel, storedprogramme, binary digital machine employing simple transistorised circuits of proven reliability.

The word length is 24 bits, and the word is used in three different ways. a) 23-bit number plus sign bit. b) Four 6-bit alpha-numeric characters. c) Instruction, comprising: 14 Address bits, 7 Function bits, 2 Modifier bits, Spare bit.

A single address instruction code is adopted, the majority of instructions being modifiable by adding to the address bits the contents of one of three modifier registers.

The very comprehensive range of instructions is designed to contribute towards the high computing speed required in this type of application, and to economise in the programme storage requirements.

The main logical units of the computer are separate 4096-word core stores for programme and data; a parallel arithmetic unit containing and adder and various computing registers; basic control logic; interrupt control logic, and data channels for input from and output to the peripheral equipment.

3.2.2. Main Technical Details The circuits used are similar to those adopted in the ARGUS computer already developed by Ferranti, Ltd. Semiconductors ore used throughout.

There are three basic types of circuit in the computer; one to provide gating functions, a temporary storage element. which in effect uses two interconnected gates, and o pulse-forn1ing circuit, used to control the transfer of

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signal within the machine. Low voltages are used, the logical 'l' being represented by 0 volts and the logical 'O' by -6 volts.

The basic logical elements are: a) The NOR gate, which consists of a diode-type OR gate followed by an inverter. This circuit uses one transistor. b) The POWER gate, which is a more powerful version of the NOR gate. This circuit uses two transistors. c) The STATICISER, which is a flip-flop circuit set according to the state of its inputs by the output from a PULSE gate. This circuit uses two transistors. d) The PULSE gate, which has a diode-type OR gate followed by a pulse-forming circuit. This circuit uses two transistors. e) The POWER drive gate, which is a very powerful version of the NOR gate used for driving peripheral equipment. This circuit uses one power transistor.

The circuits of the logical elements are standardised so that logical design and package design require no reference to the electronic details of their operation. Simple loading rules provide the logical designer with all the information required.

NOR and POWER gates are used for the gating of all data and waveforms which do not have to be held in temporary storage.

The STATICISER provides temporary storage for one bit, and once set will remain so until the arrival of a gated clock pulse from a PULSE gate.

The PULSE gates are used to set STATICISERS, and the timing of their output pulses is determined directly, or indirectly through other PULSE gates, by the output of the 500 kc/s Clock Pulse Generator which provides the basic timing of the computer.

The high-speed storage consists of separate ferrite core stores for programme and data, each of 4096 words is a 64X64X24 matrix. The 14 address bits in an instruction word enable 16,384 address to be specified so that a further three blocks of 4096 words can be added to each store, if required, without change in the instruction code.

The in:portant feature of the Apollo Computer which enables 1t t.o communicate with a large number of peripheral devices simultaneously is the 'interrupt' facility.

The arrangements are such that under normal conditions there is no restriction on the time at which any of the input keyboar_ds_ ma~ be operated (or any other peripheral unit who~e timing 1s not controlled by the computer). When a key is depressed the computing programme currently being obey~d _is inte~rupted so that the input character can be ~ead 1n 1mmed1ately by an input routine, after which the interrupted programme is automatically continued. lnterr~pt channels are arranged in an order or priority, with dev1ce_s such as keyboards at the top of the list. The computer 1st fast enough to deal with a large number of input keyb~ar~s even if they are all operated simultaneously, reading in the inputs sequentially and reaching the last one before its input signal has ended. An automatic keyboard lock is also provided as a safeguard against freak loading conditions.

A time register is provided which is updated on receipt of an external signal. This enables the computer to obey programmes on a real time basis.

3.2.3. Programming

Operational Programmes

The Instruction Code

Each operational programme is written as a self-contained programme, although it may refer to any of the peripheral equipments or to any data store address. The locations of the first instructions of the operational programmes are stored in a directory in a predetermined order of priority. When an operational programme is completed, the organisation routine tests marker words to determine if execution of further operational programmes is required, and jumps to the appropriate instruction of the required operational programme which is highest in the priority order.

A comprehensive range of instructions is provided for performing basic arithmetic and data processing. Storage capacity required for programme instructions is reduced and preparation of programmes is simplified by the inclusion of address modification, counting instructions, conditional jump instructions and automatic link storing jumps for entering subroutines. A summary of the instruction code is given in the Appendix (section 6).

The speed of computation is further increased by the inclusion of fast multiplication, division and shifts. Instructions are provided to make it easy to write programmes which perform double length arithmetic and floating point arithmetic, should these be required. Numerical data is input to the computer in the natural decimal form. This is then converted into the binary form required for computation, by radix conversion instructions. Similarly, binary data is automatically converted into a decimal representation for output.

Non-numerical data such as Trip Numbers, Call signs and Airport are represented in character form in the computer, normally stored as four characters in a data storage location. Manipulation of this data is made easier by the provision of special instructions to select and sort the characters.

The programmes to be obeyed are of four basic types: Interrupt Routines The purpose of the interrupt facility was described briefly in section 3.2.2. When a transfer to or from any of the peripheral equipments (keyboard, teleprinter, etc.) is required, an interrupting signal is generated. At the end of each instruction in the programme currently being obeyed, the logic scans, in a predetermined order, the staticisers set by the interrupting signals. If any one is set the current programme is interrupted, the number of the last instruction obeyed being stored temporarily in the data store, and control is transferred to the first instruction of the interrupt routine.

The interrupt routine preserves the contents of all arithmetic registers in use by the current programme, at the time of interruption, and performs the operation required by the peripheral equipment. A part of the data store reserved as a buffer store is associated with each interrupt routine.

If an interrupt is in operation, other interrupt routines wait until it is completed. The time for an interrupt routine should not exceed 500 /' sees. at each entry, and is usually about 100 .a sees.

Organisation Programmes An operational programme calls for transfer between the computer and the peripheral equipment by means of a jump to an organisation programme. The organisation programme sets the required transfer in operation imme?iately unless the peripheral equipment is already in use, in which case the request is stored in a directory and the operational programme is continued until the peripheral equipment becomes free.

The instructions of a programme, punched in coded decimal form, are read from paper tape to the programme store by an organisation routine.

Secondary Programmes The secondary programmes are those not directly concerned with operational Air Traffic Control, but which may be obeyed when the computer is not required by any other programmes. For example, Operational computing may be held up until the input of message is complete.

The computer obeys secondary programmes during the waiting period.

Secondary calculations consist of statistical analysis of data, routine testing of computer circuits and other such supplementary computing.

Computing Speed Computing in Apollo is performed at high speed as exemplified by the following typical programmes: Interpret and store a flight plan for a typical westbound aircraft, 33 milliseconds.

Test that the flight will not infringe separation standards with the other 100 aircraft in the system, 120 milliseconds.

Prepare four flight progress strips for the typical westbound flight, 5 milliseconds.

Of course the time to input the flight plan from a keyboard will depend on the speed of the local operator (about 40 seconds), and the time to output the flight progress strips will be determined by teleprinter speed (about 90 seconds).

For those who are more interested in calculations of a statistical nature, calculation of the arithmetic mean of a sample consisting of 10 items requires approximately 2 milliseconds computing time. To calculate the variance of the same sample requires about 12 milliseconds computing time.

3.3. Peripheral Equipment Since keyboard operators, both controllers and local operators, require a printed record as a check against typing errors, all the units can be teleprinters of one basic type.

The machine used is the Creed Model 75 teleprinter, modified for parallel operation at up to 7 characters per second. Four variants are required: a) For the teleprinter operators inserting basic data. This type has a keyboard and 0 page printer for local record only, and uses the standard Pegasus arrangement of keys and code bars. b) For the controllers. Similar to a) except that the printer is also used to print output data from the computer. and the keyboard is rearranged to give a functional layout. The key inscriptions, code bars and type faces are modified accordingly.

9

c) For the programmers. A printer without keyboard.

Standard Pegasus arrangement of code and type faces. d) For flight progress strip printing. Similar to c) but with a sprocket fed platen, and using preprinted and perforated stationery.

In operation, some standardisation of typing procedure together with the use of warning characters is necessary to enable the computer input routines to interpret messages correctly. However, typing errors are not serious, as all input messages are held in a part of the data core store reserved as a buffer until the keyboard operator is satisfied, by checking the printed local record, that the message is correct. New data cannot be used in computation or for output until the input operator presses a 'FINISH' key.

Sound-proofed housings will be provided for the teleprinters in the control room.

The two tape readers are standard Ferranti model TR5 readers which read five-hole paper tape at a rate of up to 300 characters per second.

The paper tape punches are Creed model 25 reperforators, capable of punching five hole paper tape at up to 25 characters per second. The punches have been modified io receive parallel signals from the computer.

All the peripheral equipment dealt with in the preceding paragraphs works with five bit characters, Figure Shift and Letter Shift being included as special characters. The six bit characters represented in the computer correspond to the character from tape or keyboard plus a sixth digit representing the Figure or Lotter Shift state of the character.

A set of standard tape editing equipment is provided for programmers' use, consisting of a Creed Type 75 teleprinter, with reperforator attachment, a Creed tape reader end a desk with control facilities.

The tape editing equipment makes provision for preparation of tapes by keyboard manipulation, printing from tapes on the page printer, reproducing tapes, and inserting or deleting characters on tapes.

3.4. Cathode Ray Tube Displays Experiments are to be conducted on the usefulness of displaying alpha-numerical and other information to the controllers on cathode-ray tube displays. The nature of the picture displayed is under the full control of a stored programme which feeds data, as often as is required, to the display electronics via a 24-bit register. 18 bits in this word ore used to define the x and y co-ordinates of a dot on the tube face which is to be brightened up. The definition will therefore be equivalent to 512 lines vertically and horizontally. The remaining 6 bits in the register are used for control purposes such as write, erase, select one of four displays, etc.

The display electronic circuitry which converts the contents of the display register into a picture on the tube face is being developed by the Royal Radar Establishment. A fourth bay containing this electronics and its own power supply vvill be attached to the three bays of the computer proper.

When disploying alpha-numerical characters each charncter is specified by 10 dots within an 8" 8 grid, giving ci rnaxirnum capacity on the tube face of 4096 characters (64 64). A reference point 1n each smull grid (the lop left hond corner) is used to determine the position of the charncter on the display.

10

The programme to display one character requires about millisecond of computing time, the dots in the character appearing at approximately 100-microsecond intervals.

A long-persistence tube is used to reduce the character regeneration rate. The programme refers to a character directory which occupies 120 words of storage space in the data store. 40 different characters are to be used 1 and each requires three words to specify the dot positions within the 8X8 grid.

3.5. Engineering Details It is beyond the scope of the paper to include comprehensive engineering details, and the remarks below are intended to give a general description only.

The logical circuits are assembled on printed-circuit packages about 11 ins by 6 ins in size. The package te~h足 nique of construction is now well-established and offers many advantages. In Apollo there are about 400 logical packages, of ten different types. The layout of gates and staticisers on the packages is standardised. About 75% of the packages are of only 5 different types. The average number of components on a package is about 135, including 13 transistors.

The packages are held in nylon runners, 30 to a shelf, and there are 8 shelves in each bay. Two bays are required for logical packages. The third bay contains the two stores and provision for a second data store, and the computer power pack; each of these units occupies a space equal to two package shelves. The bays are 66 ins high, 22 ins wide and 19 ins deep. When assembled they stand on a plinth housing cooling fans, and are completely enclosed by removable doors, end panels and roof panels.

The CRT display electronics are not packaged, but are mounted in a similar bay to the other three.

Attached to the computer bays are a side table to accommodate tape punches, and the control desk which also has on it the two tape readers and the programmers' printer. The control panel is in two sections, one used by the programmers, and the other, under a hinged flap, by the maintenance engineers.

The power supply consists of a 5 kVA stabilised motor alternator which works from the 3-phase 50 c/s mains and provides 3-phase 400 c/s output. The use of 400 c/s from ~ stabi.lised motor alternator leads to simplification and lightening of the computer power pack, which consists of 3-phas~ rectifier circuits and simple choke-input ripple filters, without further stabilisation.

The floor area occupied by the complete computer and control desk is about 10 feet square. The machine is designed to. ~perate under normal conditions of temperature and hum1d1ty, and no special air-conditioning is required.

The tota~ dissip~tion in the computer (excluding the display electronics which uses vacuum tubes and has its own power supply) is under a kilowatt.

Apart from the motor alternator, which must be mounted on a con~rete base, there are no floor loading problems, and. spec1al.ly strengthened floors are not required. The equipment is designed to break down, if necessary, into units small enough to pass through normal doors.

3.6. Maintenance and Reliability The reliability of the computer is expected to be high for the following reasons:

...

a) All the logical elements are in packaged form. This type of construction ensures that when a faulty circuit is detected it can be rectified in the shortest possible time simply by replacing a package. The fault can then be repaired at leisure away from the machine, by use of a package tester provided for the purpose. b) Transistors and semiconductor diodes, which are inherently less prone to failure than valves, are used throughout. c) The computer is fast enough for test programmes stored in the computer to be obeyed at frequent intervals.

Such programmes will give an indication immediately faulty operation occurs. d) The execution of regular maintenance procedures involving more comprehensive test programmes and marginal tests will further increase the expectancy of long fault-free periods of operation. e) The circuits used for the logical elements are very simple ones which work well within their limits.

The regular maintenance procedures mentioned in d) above involve the execution of diagnostic programmes to localize incipient faults detected under marginal conditions. Marginal tests are done with reduced D.C. supply voltages on one or more sections of the computer. Packages which fail with a 10% reduction are detected but not necessarily changed; those which fail with a 5% reduction are changed. Increase of clock frequency is used in a similar way.

Full details of the methods have yet to be worked out, but the principles have been well established with other computers such as Pegasus. It will be a matter of experiment to determine how frequently such regular maintenance will be required. The logical circuits used in Apollo are almost identical to those in another Ferranti computer, Argus, (Ref. 4) which was designed to meet the stringent reliability requirements of process control applications.

The prototype Argus failed only four times in over 5000 hours of operation, and all four failures were transistors in a type of circuit that has since been modified. A second Argus carried out a test of three months of continuous running without a failure.

Such results, coupled with the knowledge that fixedprogramme techniques are well-developed, lead to the belief that Apollo is capable of development into a computer suitable for operational air traffic control.

The reliability of the electro-mechanical peripheral equipment is of a much lower order, but this is not so critical since the efficiency of the system does not depend on any single peripheral device, which is in any case easily and fairly quickly replaceable.

3.7. Scope for Expansion Mention of how the system can be expanded to meet increased experimental demands has already been made in previous sections of the paper. The details are summarised in this section and some others added which have not previously been mentioned.

Storage capacity can be increased in several ways. Extra core storage up to a total of 16,000 words each of programme and data can be handled by the control logic of the computer without major modification. Provision has been made for the simple plugging-in of a second data store since the need for it is fairly certain to arise as the experiments proceed. It is not in fact I ikely that the full

complement of core storage, which is comparatively expensive, will ever be required, so some thought has been given to the possible addition of slower forms of large capacity storage, such as a magnetic drum or magnetic tape unit. Both types of store can be regarded as peripheral units which are handled by the interrupt logic under programme control.

The number of input/output channels to machines of the teleprinter type can be increased to about 100 without overloading the computer, and without introducing time restrictions on their operation.

Provision is being made for the attachment of a new type of fast flight progress strip printer which actually produces strips and which gives much more freedom of layout and form of the characters printed.

The power supply is designed to give 5 kVA, which is about 5 times the initial requirements, and should be adequate for all the likely additions to the computer logic.

Finally, the high speed, the flexible instruction code and the ease of changing stored programmes all make their contribution to the computer's ability to cope with additions to the system and a wide variety of air traffic control experiments.

4. Acknowledgment The authors wish to thank the Directors of Ferranti, Ltd. for permission to publish the paper.

5. References 1. "Air Traffic Control Plans in the U.K.".

By Capt. Hunt (of the Ministry of Aviation).

The Aeroplane 15th July 1960.

2. "Automatic Data Processing in Air Traffic Control".

By P. C. Haines.

Journal of the Guild of Air Traffic Control Officers, June 1960, p. 358.

3. "An experimental Electronic Data-Processing System for Air Traffic Control".

By J. S. MacMullan, H. S. Bray and J. A. Llewellyn.

Paper presented at the Institution of Electrical Engineers Symposium on Air Traffic Control on 8th April, 1960.

4. Ferranti Argus Process-Control Computer System.

Ferranti Lt. Publication DC 39B. London Computer Centre, Newman Street, London, W.l.

6. Appendix Summary of Apollo Instruction Code Group Group Group Group Group Group Group Group

00 01 02 03 04 05 06 07

Transfers to data store.

Collated transfers to data store.

Transfers from data store.

Collated transfers from data store.

Shifts in arithmetic registers.

Character shifts. .

Multiplication Division and Radix Conver:ion.

Transfer to f~cilitate double length wor ing.

Group Group Group Group Group Group Group Group

l0 11 12 13 14 15 16 17

Set up modifiers.

Miscellaneous register transfers.

Preserve registers in store.

Spore.

Conditional jumps.

Unconditional jumps.

Spare. c111d double modification 路 Stop instruction facility.

J

l

On the Automation of the

Roland Maier

Air Traffic Control Services in the German Federal Republic The article "Einige Gedanken zur Automatisierung des FS-Kontrolldienstes in der Bundesrepublik Deutschland" (DER FLUGLEITER, Vol. 7, Nr. 3, July 1960) has attracted much attention here and abroad. For the sake of our international readers we ore publishing this English Version which hos kindly been translated by the Technical Information and Library Services, Ministry of Aviation, London.

The constantly increasing volume of air traffic in the German Federal Republic makes it necessary in this country also to tackle the problem of the automation of air traffic control. It is sufficiently known that in other countries for some considerable time past, attempts have been made in this direction. In the U.S.A., a development centre has been set up which investigates, in some cases by theoretical studies and in other cases by practical experiment, all the problems connected with this question or arising from it.

That this is by no means a simple problem is easily appreciated, if we consider more closely the different sections comprising the Air Traffic Control Services. Basically there are three authorities in direct contact with the aircraft to be monitored and directed: the Control Tower, the Approach Control and the Area Control.

It is the problem of automation of the air traffic control services to transmit data to these three authorities and present it in a suitable form to assist the air traffic officers to form a three dimensional picture of the instantaneous position in the air. Not only must a picture of the actual position be offered but also the future, anticipated occurrences in the controlled air space must be made available to the air traffic officers on special request. The equipment which can supply this information will be discussed later.

To make the provision of these pictures of the present and future positions possible, the flights must be plotted according to an accurately defined method. This is basically achieved in the following manner: For each flight, a flight plan (course schedule) is prepared. From this flight schedule, all the data can be obtained which, in general terms, are required for steering the aircraft. With the help of the available flight schedules, the air traffic officer can prepare a provisional picture showing the air traffic and make corrections where necessary so that no accidental collisions occur. These corrections are an essential factor in all flight schedules. Reduced to a common denominator, this implies that a number of information signals must be processed.

This acquiring, sorting and computing of information signals is however only a preliminary to the actual air traffic control. It constitutes a very heavy load on the available manpower. For this routine work, equipment has recently become available which performs these processes with on almost incredible speed (about 105 operations per second) and with a reliability far exceeding human powers.

These machines are the electronic, digital computers.

An electronic computer of this type will be the central point of any installation for the automation of air traffic control. Its working features will be very briefly described.

It consists essentially of four parts: input and output unit, store computer and control unit. A large voluniP of

1'2

da~a c.an be fed to the computer via the input and output units ~rn Develop~ent Stage 1, this consists essentially of

teleprinters as will be explained later) and stored in the store. Obviously, a large volume of data can similarly be taken from the store. Computers of modern design use the so-called ferrite core stores for the store unit: these are able. to store data with great speed and reliability. The required data are passed from the store into the computer to be processed there. The computer can perform a num~ be.r of di.fferent o~erations, among others, the full range of ant~met1c ope~attons, also logarithmic operations, comparison operations etc. Data which, for a time, will no longer be used in the computer are again returned to the store and kept there. The whole combined activity according to a very complicated schedule must release the programme for the calculation. This is essentially the function of the control unit. To be sure, it is not possible in so few words to _analyse completely the method of working of an electronic computer. Also, this is not the purpose of the present paper. In this connection, the reader is referred to various published articles in the specialist publicatio "El · C ns (e. g. . ectronic omputers" pub. R. Oldenbourg, Munich and Vienna).

In addition to these few words on the manner of f _ . . f I . unc t1onrng o e ectron1c computers, it must first be stated th t there is a basic difference between an automised air fic control system and an electronic computer. In principle any more or less effi~ient general purpose computer can be used as the Key pm of an automised air traffic control system. But su~h a computer alone is not able to solve the pro~lem of. air traffic control, even with a programme e~gineer~d rn such a way. Only its co-operation with the ?1fferent rn- and output units, the main importance attaching to the output units, converts the computer into an automised air traffic control system.

From this it can be deduced that the computer is not systematically linked as the Key pin in the air traffic control system. On the contrary, by selecting a general pur~ose com~uter, we find ourselves in the favourable position of berng .abl.e t~ test any desired system, as long as the necessary indicating equipment is available and a suitable programming can be successfully performed.

The F.ederal Institute for Air Traffic Control has started from this basis ' parf1c u I or IY as up to t h e present no-where . is .there . an automised air · t ra ff.1c control safety system which might not benefit from furthe t f d h. h . satisfactor fro II . r .es mg a~ w ic is .. Y m a aspects. This basis necessitates, as a pre:equis1te, a gradual development by stages. The whole pr~1ect. has been divided into several phases, the first of which is to be realised in the following two years. This p~ase says nothing in regard to the equipment in the autom1sed control centre t o b e new Iy created, which · ·1s to b e . built up. as rapidly a s poss1·bi e, b ut .1s to be regarded purely as a trial phase.

tra~­

The Key pin of this Phase l is a high-speed universal computer, which can be fully programmed an ~fficient in and. output unit worl<ing · · s1mu 1taneously .in 'all parts on the basis of .teleprinters , and equipment · f or plotting . . situa. . air tions which ore controlled by the computer programme.

For practical reasons, the computer TR4 made by the firm Telefunken has been selected. It can be said of this computer that its possibilities are hardly utilised to the full in Development Stage 1. It is so universal that all the possibilities which are transmitted to it from the control office can be tested. The performance data of the TR4 computer are briefly indicated below: Binary working parallel computer with semi-conductor circuits; Rhythmic frequency: 2 mc/s; Microprogramme control with exchangeable slide-in units for orders; Automatic computer control and transport supervision; Purely binary internal representation of the numbers; 48 bit Fixed comma, about 13 decimal places; Eight alphanumerical signs with 6 bit Fully coded address order 24 bit (half word) Half word addressability (for the requirements of air traffic control this means an increase in the storage capacity approximately by a factor of 2); Two separately accessible ferritecore stores with 4096 and 24576 words to each 52 bit: store cycle time 6 ,11s; Fixed store of 4096 words to each 52 bit: store access time

0.5 ."s; Index store for 256 words of address length; Four in and output recorders for connection to different in and output units (e. g. teleprinters, digital data indications, synthetised air situation plotting etc.); Computing times; Addition with a fixed comma 4.5 ."s, multiplication with a fixed comma, 30 .us;

ACC i-IANNOvER

ACC f:"RA

The mean operational speed referred to ·i·he problems of air traffic control amounts to more than 100 000 operations per second.

It has already been stated that Development Stage 1 is to be regarded purely as a development and testing stage. During this it is also proposed to investigate the interplay of man-power and machine power. Man must be convinced that what the machine computes is correct. It is not necessary for this, however, to begin with the indubitably greatest problem of the automation of air traffic control, the control of the local traffic region. For this reason, we select the area control which supervises and directs the aircraft en route. In this case also, we shall not begin with a complicated, synthetised plotting of the air routes, but for this control, we compute and print the control strips for the Area Control, a procedure such as is adopted in other places, for instance, in U.S.A. This printing of the control strips is also to be introduced progressively, inasmuch as they will be printed to an increasing extent, as also the control strips for the Approach Controls and Control Towers. This decision has had to be reached on account of the relatively slow teleprinter machines.

They offer considerable advantages compared with an expensive and elaborate universal Printer. l. More favourable first cost.

2. Decentralised teleprinters can be installed at suitable sites (short distance for conveying strips).

3. Relatively little trouble during use.

4. Possibility of maintenance within the framework of the maintenance services of the teleprinter exchange.

5. Exchange of units no longer required with the teleprinter exchange (obviously the equipment must also be selected bearing this fact in mind).

•,11.<•~ulN

TWR FRANli'FURT

INPUT AND OUTPUT OF THE COMPUTER FOR FRANKFURT ACC PHASE I

1.1

The block diagram, on the opposite page, gives an impression of Development Stage 1, showing the arrangement of the input and output equipment (teleprinters) and will be explained in somewhat greater detail in the following.

Four of these teleprinters are installed for the output of data for the Area Control, in each case two being allocated for green and two for yellow control strips. In addition, the teleprinters are equipped with red-black coloured ribbon switching means so that, for instance, flights of jet aircraft can be written out in red. Three teleprinters are provided for the Approach Control and two for the Control Tower. Teleprinters are similarly used for the input of flight schedules, correction data and weather data. Also the control strips for the Control Centre at Hannover, which, during the first Development Stage is to be covered by the computer in Frankfurt, are written out on teleprinters and the corresponding flight schedules data are fed in by this means. An ordinary Duplex-teleprinter linkage is used as the Hannover-Frankfurt transmission line.

From what had already been said it can be gathered that the computer is able to receive reports in coded form.

The basic code for reasons of expediency, is the international teleprinter code No. 2 and probably later the 7 bitcode, which permits considerably higher transmission speeds. It appears desirable that this internationally fixed code should be generally adopted. Thus the essential prerequisite is ensured that computer units in different sites can correspond without any complicated conversion units.

Such a complicated batch of automatic accessories cannot, of course, be immediately incorporated into the existing service. In the interests of smooth running of the existing service, it must be required that when testing the equipment for the first time, particularly the computing programme, a parallel service is built up, i. e. the control strips are calculated and written out as previously by the methods hitherto used. In addition, the electronic computer calculates the control strips and prints them automatically at the appointed places. The two strips are compared visually. If they do not agree, the differences are determined, and on the basis of them, improvements are made in the programme. Not until, by this means, it is ensured that the computer is working without errors is the manual writing out of the strips discontinued. Thus it is not necessary from the very start to print control strips for the whole area to be controlled since lack of personnel makes it impossible to compare with each other the large number of control strips involved.

The practical solution is thus to subdivide Development Stage 1 still further. It must be expressly observed that this subdivision does not depend solely on working requirements and precedences but that the programme structure of the computer also has a very important influence on this subdivision.

written out. This involves no additional load for the computer. Thus the possibility arises of testing the co-ordination between these authorities.

Stage 2 In addition to the programme stored up to the present, there is the further part which deals with the inquiries which are fed in by a teleprinter specially provided for the purpose. It will be installed alongside the Radar Control Station. Through this unit enquiries from the Control personnel can be directed to the computer which are answered by it on the same unit (for instance, if a certain question is put, the computer will write out the whole flight course of an aircraft). The computer in turn can put questions to the control personnel which must then by answered by them (for instance, questions in regard to overdue aircraft).

Stage 3 The programme for the input and handling of correction data is fed into the computer. Thus these can be worked out by the computer. Since up to the present only flight schedules relating to the West Sector are put in the computer, it is only necessary to feed in correction data for the West Sector, since the computer would only react to other correction messages by producing an incorrect report. At each input of correction messages, the computer checks whether the flight schedule concerned is present.

Similarly, on the insertion of a flight schedule, it checks whether a schedule for this aircraft is already present and then also produces an error report.

After these three stages have been taken into service, the computer has ready for all aircraft present in the West Sector a picture of the present position. Thus already at the present stage, an automatic indicator desk for control strips (naturally for the West Sector only) can be adjoined.

Stage 4 In this stage, a documentation unit is to be tried out.

The information which must be preserved for a long period will be written out on a teleprinter specially provided for the purpose.

The extension of the printing of control strips to the remaining sectors no longer presents any difficulties. The appropriate programmes are already stored in the computer. In the following stages, it will only be necessary to expand the in and output capacities.

Stage 5 Flight schedules for the other sector also will be fed into t h e computer, the input and output capac1路r1es being su1tably increased.

Stage 1

Stage 6

The computing programme for the computing and printing of control strips for the whole region to be controlled is fed into the computer. Since, however, only those flight schedules relating to flights in the West Sector are fed into the computer, only control strips for the West Sector are computed and written out. If these refer to taking off or landing aircraft, then the corresponding control strips in the Approach Control or in the Control Tower are also

.. t II sectors also in a. . d.

The slow continuous trans1t1on . f th equiprnenr for fee 1ng fluences the number an d size o e .1n th e correc t'ion d a t a. A sufficient nurnl.Jer of. units will . 路pose so that all 111corn1ng correc b e a II ocate d f or th 1s pu1 . t b cominunicated to the computer. t ion repor s con e .

On conclusion of this Stage 6 the computer will have available for the whole region to be conti-ollecl the actuc1I cmd the onticipated future air positions The equipment foi

掳

IS

the automatic charting of the flight movements, which may be already available - the nature of the equipment still requires to be explained - can now be utilized for any desired sector. This would be quite feasible for an equipment indicating the air position in a form similar to a radar picture, and drawing its data from the computer, since now, with this equipment, continual transition from one sector into the adjacent sector is possible.

Stage 7 The frrst input units transmitted by radio will be installed; in connection with the briefing for flight schedules for civil aircraft starting from Frankfurt and the meteorological service for the input of weather reports.

This stage serves for the trial of radio-transmitted input units. It is to be regarded as the preliminary stage for the next stage.

Stage 8 The in and output units for the feeding in of flight schedules and the printing of control strips will be installed in Hannover. The input unit will appear a little different from the corresponding units in Frankfurt. The socalled safety input units will be tested which ensure that the outgoing flight schedule has really been correctly set up. A safety input unit of this type wil! similarly be set up and tested

in the computer for the feeding of programmes into it.

Since it only proposed to print initial control strips in Hannover, and correction of the control strips by the computer is not intended at first, it is not necessary to feed correction data for this purpose into the computer.

Stage 8 serves to test the transmission of data over long distances by means of teleprinter lines. Furthermore, this stage is very important from the aspect of linking up with electronic computers of other Control Centres (Amsterdam, ~ondon, Paris) which can exchange information without converter apparatus simply by way of the international air traffic control teleprinter network or special direct lines.

In this paper, up to the present, very little has been said in regard to the equipment for the automatic charting of flight movements. It is intended to equip operational posts with such equipment. In the first place, a post with automised control strips is under consideration. At the present instant, no further details can be given in regard to this post. At present, the BFS is testing the available equipment.

Efforts will be made to establish operational posts of this nature as soon as possible, in order to be able to test them also after the setting up of exchange computers.

From the results of the actual testing and the experience of the other air traffic control organisations the knowledge required for the erection of a new Control Centre will be gained.

first Civil Secondary Radar for Continental Europe The first civil ground secondary surveillance radar 1n Continental Europe is to be installed in France early 1n

1962.

The equipment has been ordered by the French Secretariot General a !'Aviation Civile for its Service Technique de la Navigation Aerienne from Cossor Radar & Electronics Limited of Harlow (Essex, England). The equipment to be supplied consists of an interrogator-responser and an aerial system. These wi II be associated with an existing primary radar located at the French Nor.them Air Traffic Control Centre (Centre de Control Regional Nord) adjacent to Orly, lhe Airport of Paris.

The equipment will be used by the Service Technique de la Navigation Aerienne to evaluate the air traffic control radar beacon systern and to gain operational experience with this new tool for the air traffic controller.

In oddition to the ground equipment the French Government are also procuring an airborne transponder from Cossor The transponder will be installed in a civil aircraft of the French Government and used for the purpose of

16

evaluating the ground equipment. Similar Cossor transponders are already in use in Air France aircraft currently operating between Europe and the United States of America.

The civil secondary radar system has already been implemented to a wide extent in the United States of America. The FAA have for some time required that all aircraft op~rating over 20,000 feet and flying in certain dense traffic areas should be fitted with airborne transponders. . A. si'.11ilar de:'~lopment can be foreseen in Europe, and !n Britain t~e M1n1stry of Aviation have already announced that by mid 1962 the carrying of such transponders will become mandatory for all civil aircraft operating over 25,000 feet. This minimum height will be lowered as implementation proceeds.

With the formation of EUROCONTROL it may be reasonably expected that future European air traffic control extension of this nature will become a matter of direct interest to them.

Flight Plans and Flight Programmes* Most short haul operations are in areas of high traffic density. In such areas we accept the economic penalties of present methods of traffic regulation because we do not know how to navigate in such a manner that avoidance of collision with other aircraft is assured. There is no lack of airspace, in the areas of highest traffic density aircraft only occupy a small part of a millionth of the navigable airspace. The problem is to develop navigation systems which incorporate adequate collision avoidance facilities, or traffic regulation systems which are less wasteful of airspace.

Although it is to be hoped that airborne equipment enabling one aircraft to avoid another will become feasible, traffic regulation must be regarded as a permanent characteristic of high density traffic areas. If the traffic density is such that action by aircraft A to avoid aircraft B might conflict with action by aircraft C to avoid aircraft D, any conceivable airborne system for avoiding collision must involve coordination which becomes, at a limiting density, regulation. Collision avoidance by freely navigating aircraft is only possible if the aircraft and other aeroplanes with which it is potentially in collision may be regarded as an isolated system.

An air traffic control system ensures collision avoidance by correlating the predicted flight paths of aircraft for some future interval of time and rejecting any one of a pair which, by the criteria of the system, might conflict.

The capacity of the airspace is determined by the separation criteria of the control system. The utilization of the airspace is determined by the capacity and the distribution of traffic flow.

Minimum safe separation criteria are determined by: A. The capacity of the control system to correlate flight path predictions and communicate the result.

B. The accuracy of prediction of future flight path.

In many areas the relatively low traffic which is sufficient at present to saturate controlled air spaces is primarily a consequence of the crude methods by which flight paths predictions are examined by air traffic control.

For example, an aircraft may be refused permission to cross an airway because the air traffic control system does not have the capacity to compute whether the aircraft will maintain separation from aircraft using the airway. This problem, which is the subject of several different projects, is outside the scope of the present paper.

Efforts to improve the accuracy of prediction of future flight path have been concerned with track guidance and the accuracy of fixing present position. Since the purpose of air traffic control is to prevent collision IN THE FUTURE, accurate knowledge of present position is only helpful in so far as it improves the accuracy of prediction of future position.

The primary uncertainty in flight path prediction, and therefore the primary obstacle to reducing separation criteria of an adequate control system, is the fact that the flight plan is not a programme, but merely a statement of how the flight would progress if forecasts of temperature, wind, and in some cases, aircraft performance were correct. The cruise mode which appears most convenient is selected at flight planning. Depending on the aircraft type and other factors it may be specified as a horsepower, a Printed with kind permission of Deutsche Gesellschaft fiir Ortung und Novigation.

J. E. D. Williams

thrust, an indicated airspeed, or an indicated Mach number. Subject to circumstances unforeseen at flight planning, such as severe turbulance, fuel shortage, engine failure, etc., the flight planned cruise mode is followed. No attempt is made to maintain the flight planned ground speed, or to arrive over check points at estimated times. The flight plan is not a flight programme.

The significance of uncertainty of flight path prediction has been shown in this general way in order to emphasize its relevance to any collision avoidance system which may be developed for short haul operations. The practical effects can be seen more clearly in an actual system such as an airway.

The capacity of an airway at a specified flight level is determined exclusively by the criteria for nominal longitudinal separation. Predicted separation must be sufficiently large to ensure that no aircraft can catch up with the one in front. There are clearly three parameters which control the longitudinal separation criterion: the frequency with which present position is reported (determining the duration of the period for which separation must be predicted), the accuracy of reporting present position, and the accuracy of speed prediction. It is now possible to determine present position with an accuracy which makes the possible error in predicting aircraft progress the determining parameter.

In the past, the navigation and cruise control procedures necessary in order to maintain a programmed rate of progress was impractical, and the performance of propeller driven aeroplanes made such a proposal extremely unattractive. With the advent of doppler and DME, and the general use of turbojets with a large range of economical cruising speeds, this is no longer true. It is possible, if the flight planned true airspeed is correctly selected, to maintain a programmed rate of progress with an accuracy which should enable the possible utilization of airways to be increased by a factor of 2 to 6 depending on other factors.

Jet aircraft are, of course, extremely sensitive economically to operating techniques. In a relevant investigation by the author, those elements of operating costs which are variable with cruise procedure were plotted in arbitrary units against true air speed for the flight level of minimum cost and the two flight levels next below. The temperature is assumed to be standard / the aircraft one which has been largely sold for short to medium range operations, the weight appropriate to a point 300 miles from destination.

It was found that the manner in which operating costs vary with cruise mode is a complex function of the oper.·ator"s characteristics. To take one detail as an illustration, in one airline a 5% reduction of flight time means a 50/o decrease ·in crew costs-in · anot h er arr · 1rne · · - var·iations of fl 1ght minor time have no effect at all on crew costs. Nevertheless, the values assumed for the study are fairly typical and varra. lions from one operator to a not f1er h av e only the effect . . . t o tf1e Ie ft 01 · the right and chang o f d .rsp Iac1ng t h e m1n1ma . · cost units. .. rng the monetary equ1va 1en t o f tf1e arbitrary Variations of the characte,-istics of ind1vrdtJcd operatms or of particular aircraft, do not alter the significance of the findings of the investigation to the theme of this pope1 which is that from the point of view of o 1et operator it 1s better to fly at the right altitude at Cl speed substant1olly higher or lowe 1· than the optimum than 1t 1s to accept one i/

flight level lower than the optimum and fly at whatever speed the operator chooses. If, for instance, the flight plan had been prepared on a basis of 470 knots TAS, a deviation of 卤50 knots true air speed in order to maintain the flight planned progress costs no more at the optimum flight level than clearance at one flight level lower than the optimum with freedom to cruise at will.

On some short haul routes in high density areas, the probability of obtaining the preferred altitude with current nominal separation criteria is 25% and decreasing. It may be shown that if jet aircraft maintained programme with the accuracy which doppler and DME permit, and within the economic limits of aircraft performance, longitudinal separation at jet altitudes may be reduced by 50% or more (depending on the characteristics of the control system).

Hence the economic case for flight programming to the extent of ground speed regulation to maintain flight plan is evident for airways currently saturated.

Flight programming in this sense of maintaining flight planned progress increases air space utilisation by enabling reduction of the criteria for nominal separation.

A further air space utilization can be obtained, when necessary, for the same criteria, if ATC specifies the programme. For example, on a~ airw.ay, ATC must rejec~ a requested clearance if the aircraft s programme conflicts with another at some future checkpoint. Instead of a simple rejection ATC could, in such cases, specify a revised time of arrival at the checkpoint as a condition of clearance.

The example is a special case of the general principle of increasing airspace utilization by reducing the losses inherent in a random distribution of aircraft in the traffic pattern. Where routes cross or converge there are zones of particularly high traffic density at which the demands for airspace are particularly heavy. Arriving at such bottlenecks, by different routes, at random intervals, aircraft tend to bunch, with the result that some have to accept undesirable clearances although the bottleneck is not in use for a substantial part of the time.

To illustrate the problem, consider a hypothetical gate which can accept one, and only one, aircraft in each two

minute interval so that it is theoretically capable of accepting 30 aircraft per hour. How many aircraft one would expect in a random flow to be rejected at the gate as a percentage of the number of arrivals? When the demand is only 50% of the theoretical capacity, 38% of these are rejected. Real ATC bottlenecks are of course much more complicated than this simple model which only indicates the order of increase of utilization of airspace of a given capacity if arrivals at bottlenecks could be fully programmed.

The principle of adherence to flight planned times of arrival clearly imposes a degree of restriction on operating freedom. The increase of airspace utilization by the reduction of the random element need impose no further demand on operational freedom. If ATC were to propose a programme to an aircraft as a condition of clearance, it would be because the desired clearance could not otherwise be obtained. An aircraft rejecting such a programme would lose no advantage it would have had if the proposal had not been made.

An important factor in the evaluation of a proposal to relieve the traffic problem is its status for further development in the more distant future. The next logical development on short haul routes would be the clearance of the entire flight programme prior to take off, apparently the only way to eliminate holding periods at destination. Such a procedure would involve little development of operating techniques in the aircraft beyond those suggested in this paper, but would require a new order of capacity in the ATC system. As the ultimate development along these lines one might envisage the operator's flight planning systems obtaining clearances on the most economic programme which traffic permits by iterative interrogation of the ATC system before flight, subsequently telemetering the aircraft's navigation/cruise control system with the appropriate instructions. If there is to be traffic regulation, maximum utilization of the airspace with acceptable economy can only be obtained by pre-flight clearance of the entire programme (including the landing) and, for the reasons discussed in the flrst paragraph, it rather seems that for short haul operations, ATC is here to stay.

~11" A - 1J"lhe ~rnstoh.J1t du Transport Aerien The lnstitut du Transport Aerien which we quoted at several occasions has been subject of various enquiries of our readers. In reply to these we are today reporting about aims and objectives of this organisation.

ITA is an international non-profit association which studies, for the benefit of its Members, the economic, technical, legal and policy aspects of civil aviation. These different subjects are studied not only locally, nationally or regionally, but also on the bro_ader international basis.

The working languages are English and French.

Policy decisions are made by the Board of Directors, of which Mr. J. Roos is the Chairman. All Full Members may attend and vote at the General Meetings, which take place al least once a year, and thus participate directly in the planning of ITAs working programme. .

The management and experts are me~bers of various Commissions and attend numerous meetings - both nationcil and international - where technical or economic matters are discussed. Contacts are maintained with personalities oncl responsible quarters specializing in air i rcinsport ond oircroft construction.

18

To illustrate ITA's originality and to show its contribution to the air transport industry, it can be said, in short, that: as an international association without limiting affilitions of any kind - commercial or governmental it cannot be suspected of acting as judge in its own cause or of subordinating, even unconsciously, certain judgements to special obligations or interests; the mere diversity of its membership would suffice to compel ITA to adopt an entirely unbiassed attitude; ITA considers air transport not in isolation, but in its relationship with all sections of economy, with emphasis on the travel market and other transports media; its permanent staff of economists, technicans and jurists has first-hand experience of air transport and its problems.

路 4, rue de Solferino. Paris VIie. France

contd. poge 30

Jesse Sperling

ACCESS Down-to-Earth Air/ Ground Communications Jesse Sperling is a graduate of Georgia Tech and Columbia University. After 10 years at Western Union designing custom-made private communications systems, he joined GPL Division - General Precision, Inc. During the design and development of the General Precision Air Traffic Control Data Processing Central his interest centered on the operational requirements of the Air Traffic Control System. On the ACCESS program, Mr. Sperling was responsible for the operational analysis of the system.

ACCESS, short for Air Craft Communications Electronic Signalling System, is a semi-automatic air traffic control communications system. It is a companion subsystem, developed jointly by Motorola, Inc. and General Precision, Inc. to work with the semi-automatic Data Processing Central Air Traffic Control System.

This article will explain ACCESS from the point of view of the system users. It will answer the universal question, asked by controllers and pilots about any new system "What will it do for me?"

ACCESS is supposed to:

1. reduce channel crowding by better organizing ATC communications; 2. reduce voice communications; 3. reduce controller-pilot workload; 4. increase system reliability; 5. maintain voice flexibility; 6. more effectively utilize potential of ATC automation program.

Critical Problem of Communications Automation Attempts at automating the communications between controllers and pilots date back 15 or 20 years. No completely satisfactory solution has come out of this previous work even though the techniques and transmission speed state-of-the-art has been adequate for years.

The critical problem which defied solution until now has been that of information entry: How does a man tell the machine what to transmit?

The earliest attempts were based upon the use of a standard teletype keyboard. It is obvious why this was not successful, because the keyboard's competition lay in the case and speed of a mike button. Any automatic system, to be accepted by the pilot/controller, must exceed the convenience and utility of voice communications.

The use of a combined keyboard or one where a single key represented a word or phrase as opposed to one alpha-numeric character came closer to the solution, but still left much to be desired. The critical problem is and has been that of information entry.

Entry Problem Compounded

by Continuously Changing Control Environment Controllers and pilots are a hardy breed. They do things in the daily conduct of their work which are of course "impossible". If a system engineer had attempted to design an ATC System from scratch, and were to compile a list of duties which these men would perform, logic would dictate that his system requirements wou!d be impossible to meet. His conscience would force him to scarp

his system then and there. So, like the bumble-bee who does not know he is aerodynamically incapable of flight, the ATC System operates because it doesn't know that it can't. The secret ingredient which makes the system operate successfully is the fantastic ability of the people.

People, who have long experience dealing with the infinite combinations of variables of wind and weather, aircraft flight characteristics, pilot individualities, route structures, and so forth, are able to apply mature judgments to the continuously changing set of problems presented to them by the dynamic ATC environment.

Control decisions are made after consideration of these factors. Each of these variables has an influence to a greater or lesser extent upon the controller's resolution of the problem presented to him. The decision, based so much upon experienced judgment, is not easily delegated to a machine because the man's thought processes, perhaps without his conscious awareness of it, have evaluated the variables involved. At one time one group of parameters are more critical than others. Under another set of circumstances another set prove to be the critical ones. These changing criteria are difficult to machine instrument.

Inasmuch as all of the communications between the pilot and controller cannot be automated, voice capability remains a necessity to cover the routine messages of variable content, explanatory messages, advisory messages, and above all, emergency messages.

The continuously changing variables of the ATC environment have defied complete standardization. Yet, closer examination shows that standardization in a large degree has become possible in phraseology. Is this the secret which will open the door to automation of the ATC communications? Unfortunately, this approach has not yielded successful results in the past, because standardization of the phrases is in reality only a standardization of the order in which the words are used.

Where, then, does the answer lie? It lies in combining a semi-automatic communications data link with a semiautomatic data processing system such as that presently being evaluated at the National Aviation Facilities Experimental Center (NAFEC}.

Solution to the Information Entry Problem It is operationally fortunate that ACCESS can draw upon information previously entered into the ATC D~ta Processor for other purposes. This results in an information entry capability, which compares favourably with the convenience of the present voice system.

The Data Processor, combined with ACCESS, credatesf •f e workloa o . · an extremely powerful tool for re I1eving 1 1 d . .t 1 1 both pilots and controllers. The computer has .st~re ~ the aircraffs flight plan. In addition, it is kept in ~rmec of ·t has this vital tro each aircraft"s progress. lnasmuc I1 as 1 .

11 ftc information it can be used to materially ossi.st the P. ot~ and the controllers to communicate, by enabling each ot . · b sirnr)le pushbutton ope them to exchange 1nformat1on Y ration using the Data Processor to compose and ACCESS · certa111 · var1a · bi e 111 · fo 1·n1at1on , which would to transmit

f

normally be difficult to delivei- automatically.

19

ACCESS is a Controller/Pilot Tool Any system which attempts to automate even a portion of the ATC environment must recognize and utilize to the maximum, the experience and judgment of the people using the system. For this reason, all critical decisions are made by the controllers, who then instruct ACCESS to communicate their decision. ACCESS makes no critical decisions. It only acts as an agent, by communicating the man-initiated decisions rapidly, at machine speeds.

The system is based upon the operational requirements of controllers and pilots, for indeed it is and must be subservient to their real requirements.

ACCESS is a combination automatic digital/voice system. The philosophy which underlies the system configuration is that the entire communications load between all aircraft and the controllers on the ground is divided between the automatic and the voice subsystems. The communications which are deemed to be routine or easily automated will be handled by the machine and those which are non-routine or dynamic will continue to be transmitted over the voice portions of the system.

A combination digital/voice system enables the machine speaking in its language of binary digits, to time share the circuit with the controllers and pilots who use voice. Since digital transmission is so rapid, the time sharing represents almost imperceptible interference with the controller or pilot. The system is disciplined to sandwich the digital messages between the voice transmission. For example, an average clearance, delivered by a controller talking at an extremely rapid rate of 200 words a minute would deliver the clearance, one way without repeat-back, in approcimately 10 seconds. The digital equivalent requires 1h of a second to transmit. One third of a second is considerably less than it would take the controller to recognize the completion of the pilot's voice message and to press his mike button in response. Not all digital messages take as much as 1h of a second, so that after the controller releases his button and before the pilot can answer, a greater number of shorter digital messages will probably have been transmitted in the "dead time" between voice messages.

time of passage of a fix. To simplify the airborne equipment, we have introduced a radial departure into the position reporting message exchange; the ground makes the position report to the aircraft (see Fig. 1).

As you know, the present system of position reporting is highly redundant for safety. Each position report contains the location identifier and actual time of arrival for the fix reported, the location identifier and the ETA of the next fix, the identifier only of the fix following, and the altitude. ACCESS will provide the same margin of safety of the existing manual system by composing a position report to the aircraft. The position report message from the ground is identical in content to the position report which the pilot is required to make under present ATC procedures. The "position report" is received on the aircraft's miniature printer.

When the pilot presses the "Report" button the airborne equipment composes, in compact machine language, a message which contains four characters of aircraft's identification and one character identifying this message as a pilot position report. The time of receipt is added by the ground equipment. This time is considered by the computer to be the actual time of arrival over the fix.

With this information, the computer can easily compose the position report message for the pilot, since it knows beforehand both the fix which the pilot is reporting and his approved flight plan.

Airborne and Ground Based Equipment

The pilot, in response to this information, presses the "Acknowledge" pushbotton or if he disagrees, he makes this known to the controller by voice. Only after the pilot has verified the accuracy of the "position report" message by means of the "Acknowledge" button does the Data Processor perform its processing functions. In the case of the position report which has been acknowledged by the pilot, the Data Processor treats this in the same manner as a manual entry of position report into the Data Processor by the controller. It searches its files to determine if this aircraft will be in conflict with any other aircraft. If requi~e.d, it updates all flight progress strips affected by the position report. It produces required but not-yet-prepared flight progress strips for any fixes ahead, and it indicates to the controller of jurisdiction that a position report has been made.

There follows a series of examples of how the System would be used by controllers and pilots.

In these examples the controller is assumed to be controlling traffic in a sector equipped with a DPC console modified for semi-automatic ACCESS communications.

The aircroft is assumed to be an air carrier equipped

. The controller, un.der. ACCESS procedures has no position report com~un1cat1ons duties at all. After the pilot and ground equipment have completed their information exchange, the controller, by means of an "Update Lam " and an updated flight progress strip, is presented with end result: the updated position report.

with:

ACC~SS se:ves. the controller with an important backup function. His flight progress strips continuously display the necessary information by which he can control his flig~ts. Each. cont:oller scans his strips and by means of the information displayed ' knows the t'1me w h en eac h a1r路 c.raft under his jurisdiction is supposed to report his position.

1. Minimum Airborne Digital Equipment (MADE)-MADE is Cl piece of equipment which is added to the aircraft's existing radio communications receiver/transmitter.

MADE enables the aircraft to send and receive digital messoges on the existing voice frequencies.

2. A printer smoll enough to fit in the instrument panel of an oirplane, which will print out ground-composed digitol messages.

ACCESS Position Reporting A rnojor proportion of the messages in any IFR flight deol with position reporting. In ACCESS, the pilot makes lrn position report by pressing o "Report" button at the

20

t~e

Normally, the controller establishes a time limit for position report in his mind, after which he will check on the flight. .In the case of ACCESS, if no position report has bee.n rece1ve.d by ET A plus 3 minutes {or any other predesignated time) the system will warn the controller that the position report has reached its time tolerance. The system only serves to warn the controller. It neither acts nor dictates action to him. The controller at his discretion I

I

@

UPDATE LAMP INOICATES A275 HAS MADE POSITION REPORT.

rT\ \V

"A275 OVER CRIB AT 15, AT 3000 CLIMBING ESTIMATE GRANO BEACH AT 25. SOUTH BENO" GROUND RECEIVES POSITION REPORT SIGNALS ANO COMPOSES ITS UNOERSTA"<O•NG OF THE PILOTS POSITION WHICH IT TRANSMITS TO THE AIRCRAFT PRINTEP

c;?>

\ RADIO SELECTOR

I

® F~•G"'

""OGRES5

s-«:P uPa:.·rn

"----,/ Figure 1.

Position Report.

can continue machine interrogation or contact the aircraft on voice.

ACCESS has another feature of importance. Position report information is automatically entered into the Data Processor as the flight progresses. By means of this information each controller's flight progress strips are continuously being updated and are, therefore, current. Radar controllers use their flight progress strip as a back-up.

They normally keep their aircraft separated according to radar separation criteria, but should the radar fail they can quickly change from radar to conventional separation.

Under such circumstances ACCESS can immediately revert to all-voice operation and the controller can handle the emergency with the same speed and flexibility available to him under present voice radio.

In normal practice, the Ground Controller, after coordination with the Air Route Traffic Control Center issues a clearance to destination. The air traffic clearance issued prior to departure will normally authorize flight to the airport of intended landing.

If the aircraft is to be cleared short, the Ground Controller selects, by simple pushbutton operation, one of a series of standard departure routes from the runway to the first airway specified in the route of flight to the pilot's destination. If the controller instructs the DPC to deliver this aircraft's clearance to first point of intended landing, the DPC shall deliver the stored filed route of flight to destination along with the selected standard instrument departure route.

The aircraft in Figure 2 is to be given a short clearance to the CRIB intersection.

Advantages to the Pilot

The controller presses his "Clearance" button (SID 2) which instructs the system that he wishes it to deliver a short clearance to CRIB. He also presses the FD/ID button alongside of the aircraft's flight progress strip. This action further instructs ACCESS that he wishes the clearances to be delivered, in this case, to A 275. The Data Processor composes the clearance message which is printed in the

ACCESS provides a number of advantages for the pilot in making compulsory position reports. The pilot presses his "Report" button as he passes over the fix. The airborne equipment "minds the store" and makes the Position Report for him on the next interrogat!on cycle of the ground equipment. The pilot does not have to monitor the circuit until the controller is free. He reports his position using only two pushbuttons. Entry of information into the system is greatly simpl ifled. Clearances - Automatic delivery of clearances to pilots are a further example of what the ACCESS System can do to relieve the workload of both controllers and pilots.

The Data Processing Computer has the route of flight stored in memory. The route to destination is therefore known and is easily accessible. The flight path stored in the computer may not include the route from the origination airport to the first airway contained in the filed flight plan. However, a number of standard instrument departure {SID) routes can be stored in the computer's memory.

aircraft on the miniature printer.

After the pilot reads the clearance he ackn~wle~ges by pressing his "Acknowledge" button. This extinguishes the "Clearance Lamp" on the console so that the controller . d d nderstood the k nows that the pi lot has 1·ece1ve on u clearance.

Clearance to destination would require that the con t shown) 1n addition troller presses another pushbutton (no to the SID 2 button.

Notice that there is no need for a verbal repeat back from the pilot. The system hos error checking c1rcu1try built ·into ·1t which · · tf1ot if a messoge 1s· received assures t h e users at al!, it is correct. If it is not received 1nit1olly. the system will automatically retransmit and totol foilure is outo

21

® @

CONTROLLER ADDRESSES A/C FP/10 LAMP GOES ON FP/ID LAMP IS EXTINGUISHED

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DME

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PILOT ACKNOWLEDGES

Q

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@ f.'AR~~~E~L~~:~~ ~~TCRIB INTERSECTION, VIA VICTOR 6, RIGHT TURN AFTER TAKE-OFF. MAINTAIN 090 HEADING UNTIL CROSS VICTOR 51, MAINTAIN 3000 CONTACT CHICAGO DEPARTURE CONTROL 119 9 AFTER TAKE OFF"

(i)

RADIO SELECTOR

Figure 2.

CONTROLLER SELECTS CLEARANCE TO .. CRIB ..

BY PUSHBUTTON

@

CLEARANCE LIGHT GOES ON INDICATING A/C HAS RECEIVED CLEARANCE.

@

WHEN PILOT ACKOWNOWLEDGEMENT IS RECEIVED LAMP IS EXTINGUISHED

Short Range.

(see Figure 3). The transferring controller presses his "Control Transfer" button. The "Control Transfer Lamps" alongside of the A 275 flight progress strips on both consoles start to flash. The receiving Controller knows that he is being requested to accept A 275. He accepts, by pressing his Control Transfer Button. When he does so, the data processor turns both "Control Transfer Lamps" steady indicating that the receiving controller has accepted the transfer. Simultaneously ACCESS transmits the change frequency message to the pilot's airborne printer: "A 275 change to 120.2."

matically reported. Any special clearance instructions, such as fix location or time when climb is to begin, a "release time" and/or a "clearance void" will be delivered by the Ground Controller, by voice.

If the pilot for any reason wishes to request a change in the clearance this will be accomplished by voice. The controller has the ability to repeat the clearance if required. And further, he has the option to deliver the clearance either automatically or by voice.

A pilot on the ground, busy with his check list prior to take-off, or a pilot in flight getting a re-routing, each receives major assistance from the ACCESS airborne printer which automatically copies his clearance for him. Not only does it relieve his cockpit workload, since he does not have to write it on his scratch pad, but it allows him to better manage his cockpit time. He may within narrow time limits delay reading his clearance so as to complete one of his cockpit duties. Yet, this delay is not imposed upon the controller.

The controller in turn is benefltted by the fact that he does not hove to repeat any portion of the clearance missed by the pilot or listen to and verify the repeat back.

. Notice that after the pilot has changed frequency, the pilot and both controllers involved in the transfer of control have a positive indication that communications have been established on the new frequency.

Transfer of Control

Change of Altitude

As each flight proceeds the control jurisdiction for it on the ground 1s transferred from one controller to the next. Under present procedures transfer of control has two parts; the ground-to-ground coordination between controllers for the hand-off and upon agreement, the ground-to-air message to the pilot to change to the next control sector frequency. ACCESS can effect the entire ground-to-ground and ground-to-air communications trc111soct1ons through the action of only two pushbuttons

A change of altitude involves agreement between pilot and c.ontr_oll_er, based upon the fundamental precept that the pilot is in command of his aircraft and has the final say as to the conduct of his flight. However, normally no question arises and the pilot responds affirmatively. It is possible for the Data Processor/ ACCESS to generate a change of altitude message automatically as a result of controller initiation of such a message (i. e., a probe to insure that the new altitude is conflict free). It is not con-

The pil~t does not ~a~e to acknowledge the message.

The selection of the 1nd1cated frequency serves as his acknowledgement, since ACCESS is searching for the flight on the new frequency. Receipt of the machine signal on the ground serves as the pilot's acknowledgement. This signal extinguishes both "Control Transfer Lamps", indicating the completion of the hand-off .

TRANSFERRING CONTROLLER

AIRBORNE.

RECEIVING CONTROLLER

@CIT LAMP HASH($

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DME

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PB

RADIO VOLUME '<~ma

LOW LE

RADIO VOLUME KNOB tSTEU

LEV

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PRINTER READS OUT• "AZ7~ CH•NGE TO 1zo.z•

©_PILOT CHA>;CES FREQUE .. CY

RADIO

SELECTOR

Figure 3.

sidered advisable to change the computer flies and make the appropriate updates on the flight progress strips without pilot acceptance of the altitude change. Therefore, after the controller has decided that the probe is acceptable to him, he instructs ACCESS to transmit the change altitude message. The Data Processor waits for the pilot's acknowledgment before it processes the information. After pilot acknowledgment the Data Processor updates all affected flight progress strips.

Digital/Voice Division Criteria The controllers and pilots communications workload have been studied to decide which of their transmissions can be automated and which must remain on voice. The division between automatic or voice delivery was based upon the following criteria:

Machine Delivery 1. Messages which require a great deal of airtime for reading and repeat-back, and whose information content is known to the system so that Data Processor can be instructed by relatively simple pushbutton operation.

Examples of this type of message are clearances both long and short range, approach control standard advisory information {i. e., runway in use, altimeter setting, NOTAMS, winds, etc.)

2. Frequent message types which can utilize the existing capabilities of the Data Processor {e. g., Position Report).

3. If the task is one which the controller must do anyway, then the system by the required actions can be instructed to communicate with the pilot (e. g., altitude change instructions as a result of a DPC altitude change probe).

Voice Delivery l.

Short messages which can be more simply said then machine addressed to the aircraft (e. g., vectoring instructions).

Control Transfer.

2. Non-standard information to the pilot {e. g., traffic information, advisory information).

3. Emergency instructions.

4. Negotiations between pilot and controller.

5. Non-routine transmissions {e. g., late position report, and on request frx reports).

In the design of the system the integrity and prerogatives of both the controllers and pilots have been maintained. Their operational needs have been kept continuously in focus as the design progressed. The concept makes the system available to them, as a tool, which they use or not as their evaluation of the operational situation dictates. Voice, digits, and the reservoir of ATC data stored in the data processor provide controllers and pilots with a flexible, rapid and convenient communications system. ACCESS, by serving their real operational requirements, will relieve them of their clerical chores and allow them to concentrate on their primary responsibilities; controlling air traffic and flying the aircraft.

Two further Decca airfield control radars for Iceland The airport at Reykjovik, capital of Iceland, is to flt Decca airfield control radar to provide final approach talk-down facilities. This type of equipment, the Decca 424, has been in service elsewhere in Iceland for several years and the latest order for two additional radars, the 19 62 first of which will be installed at Reykjavik early in d ' is the result of very successful operating experience un er exacting conditions. . . . . .k . d .· . II by Icelandic A1rl1nes and . .

Rey k 1av1 1s use pr 1nc1pa Y . b b . of 1x1vate operoto1 s lcelandcm, as well as y a num er _ . .

11 and the Decca 424 will assist in the loco! control ot a . II y u nder conditions of bad v1s1b1l1ty; the era ft , especra . weather in this area can deteriorate ve1·y rnp1dly and an aid of thi~ na~ure hos become essenhcrl for mointo1111119 scheduled services.

ICAO Communications Division completes work

A month-long session of the International Civil Aviation Organization's Communications Division has finished in Montreal with the adoption of a series of recommendations to guide the future development of aviation communications and radio and radar navigation aids. The meeting - the Seventh Session of the Division - was attended by representatives from 37 ICAO member states, one nonmember state and six international organizations. Its Chairman was D. J. Medley of Australia; vice-chairmen were Vicecomodoro M. M. Brigante of Argentina and Dr. P. D. McKee! of the United States of America.

Following is a summary of some of the Division's recommendations, which must be considered by the ICAO Air Navigation Commission and approved by the ICAO Council before they can come into effect:

Instrument Landing System. The use of the present !CAO-standard Instrument Landing System (ILS) is now normally restricted to weather conditions in which the bottom of the cloud base is at least 60 metres (200 feet) above the runway, and there is a forward visibility of at least 800 metres (one-half mile) below this base; jet aircraft may require even better conditions. The Division was of the opinion that modifications could be made in the ILS to allow landings under lower conditions. It therefore set up three categories: Category I will cover the present ILS; Category II will make it possible to land if weather conditions are 30 metres (100 feet) for cloud base and 400 metres (one-quarter mile) for visibility; Category Ill will permit instrument landings under all weather conditions (unrestricted by cloud base and visibility requirements). Although the Division found that it was impossible, with present knowledge, to decide whether the ILS was capable of being developed to give satisfactory performance for all-weather landing under Category Ill, complete technical specifications for Category II were established and these, when put into operation, should reduce the number of aircraft forced to divert to alternate aerodromes under bad weather conditions.

The Division adopted complete new specifications for secondary surveillance radar. These specifications allow for 4,096 different coded replies from aircraft being interrogated; these replies include, in addition to identification, height information in 100-foot (30-metre) increments covering a range of 128,000 feet (40,000 metres), as well as codes for recognition of an aircraft in an emergency or with radio communications failure.

Channel Requirements for Short-Range Navigation Aids.

The existing !CAO-standard short range navigation aids are VOR (very high frequency omni-directional radio range) which gives the aircraft its bearing from a ground station, and DME (distance measuring equipment), the distance also being given from a ground station. In areas requiring many VOR installations the number of radio frequency channels now available is barely sufficient for present operationol needs; since there will clearly be future requirements for additional VOR's in such areas, and many of these ore likely to require an associated DME, the Divi-

24

sion concluded that there was a need to provide additional VOR and DME channels.

At present, the separation between adjacent VOR channels is 100 kilocycles/second. Recognizing that the only practical technique to provide more channels would be to reduce the separation between them, the Division decided to reduce the channel separation to 50 kc/s. In the case of DME, which works on the principle of an interrogating device in the aircraft with a transponder at the ground station, a second mode of interrogation and response was adopted which will make more DME stations possible.

Implementation of new channels which in any way affect international air services would be left to regional agreement. After such agreement, restricted use - without affecting other international services not so equipped _ by suitably-equipped aircraft could begin after 1 January 1966, while unrestricted use would be acceptable after l January 1970.

Distress Procedures. The Division revised the distress urgency and safety procedures for radio communicatio~ now contained in the ICAO international standards and recommended practices. The purpose of this revision is to ensure that the ICAO procedures keep pace with modern air transport operations and are coordinated with similar procedures used in the maritime services, thus providing the maximum possible assurance and effectiveness of communications assistance the mobile stations in matters pertaining to the safety of human life.

Problems in the High Frequency (HF) Radio Band. An Extraordinary Administrative Radio Conference is to be convened by the International Telecommunication Union to revise the high frequency (HF) allotment plans for the aeronautical mobile service. From the point of view of international civil aviation, there are several fundamental questions which will influence the pending revision of the HF plans. These questions include: will the requirements for HF channels continue in all regions, or will other developments in communication techniques take over some of the burden; should the present channel-spacing be maintained or should smaller channel separations be developed to give greater spectrum economy; would the existing method of communication (double side-band radiotelephony) continue to be used, or should provision be made for other methods and types of transmission such as radioteletypewriter, data links and single sideband emission.

The Div_ision therefore recommended that a special ICAO meeting ~f worl~wide scope be convened next year to prepar_e the 1nternat1onal civil aviation position for the ITU meeting. All states having an interest in the revision ~f _the Frequency Allotment Plan should be invited to participate.

In considering the subject of single side-band emission the Division was of the opinion that it is not possible a; this time to prepare a detailed policy on the possible future of S~B .. It therefore suggested that, if the special ICAO meeting is held next year, its agenda should include

the subject of d evelopments in HF single side-band systems for the a ero nautical mobile service.

Need for More Very High Frequency (VHF) Channels.

As there is a conside rabl e shortage of ass ignable fr equencies for a e ronautica I purposes in the band from 118 to 136 megacycles per seconds, the channe l-separation of 100 kilocycles/second wi II be reduced to 50 kc/s, as from 1 January 1964. Any airborne equipment limitations for 50 kc/s sepa ration are expected to disappear in the 118132 mc/s portion of the band by 1 January 1964, and in the rest of th e band two yeors later; this will mean that the full appl ication of the new spacing wi ll have to be carefully considered in regiona l planning until a ll a irc raft ore

equipped to use it. Additionally, provisions were made to con tinue 100 kc/s channel-spacing in areas where the planning of radio frequenc ies does not p resent a major problem.

The Divisio n also decided that a protection date of 1 January 1972 should be set for the new 50 kc/s channelspacing equipment, guaranteeing that equipment to supe rsede this would not b e required until at least that date.

Howeve r, it was al so agreed that the use of frequencies oth e r than those based on 50 kc/s channel-spacing should be made possible by reg ion al agreeme nt a fter 1970, p rovided that arrangements are mad e at this time to enable all aircraft ta o btain the se rvices they require without undue ope rationa l restriction.

IFATCA Representatives at the Sixth Conference of US' Air Traffic Control Association Vice Preside nt Mau rice Cerf of Paris and Treasure r Henning Throne o f Copenhage n represented the Inte rna tional Federation of Air Traffic Controlle rs' Associations at ATCA's sixth annual conference in Miami Beach , Florida .

William G. Osmun, Ed ito r Bus iness/ Comme rcial Aviation, took this photo for us, showing Maurice Cerf (r.) and Henning Throne (c.) whi le they are discussing a new radar display with GPL"s Director of Air Traffic Control Department, Cro :g F. Timmerman (I.).

25

The Flarescan Instrument Landing System The Federal Aviation Agency is to carry out in the next few months tests of a new all-weather landing system, known as FILS (Flarescan Instrument Landing System). The system was developed by Airborne Instruments Laboratory.

It is designed to complement existing ILS equipment and plays no part except in extending the latter from glide slope to flareout. Eventually it may be coupled to the autopilot but in its present form it is intended merely to give flareout and landing guidance to the pilot so that he can complete his landing without external reference.

FILS consists of a ground transmitter producing signals which require a receiver-decoder in the aircraft. The latter should not weigh more than 20 lb, AIL estimates (or 40 lb in a dual version).

The FiLS antenna, located about 2500 ft behind the glide slope antenna, radiates microwave energy at a frequency of 16 OOO me to give the precision beam required for flareout. The beam, which sweeps up and down 10 times a second, is fan-shaped in azimuth but only 1 h~ thick in the vertical plane. The position of the beam is identified by the pulse repetition rate, which is made to vary with elevation angle: the spacing between individual pulses ranges from 16 microseconds at 0 elevation to 96 microseconds at the maximum (20 ) elevation angle, corresponding to pulse repetition frequencies of 62 to 10 kc/sec. The beam intersection with the ILS glide slope will naturally be farther out and higher at the higher elevations, and any one beam elevation can be selected in order to initiate flareout at the altitude and distance suitable to the aircraft type.

In operation, the FILS receiver is pre-set to indicate when the aircraft has intercepted the beam desired. As the aircraft proceeds down the ordinary ILS glide slope, the horizontal pointer of the FILS indicator moves slowly up toward mid-scale (on beam) position. When the selected transition point is reached, an indicator lamp lights up to tell the pilot to initiate flareout.

In addition, the pilot will have selected another .FIL~ beam to provide "terminal angle" guidance, i. e. to indicate the shallow final glide path angle which is optimum for his type of aircraft during the final moments of ~are颅 out. Immediately the indicator light goes on, he switches his eyes from the ILS indicator to the FILS cross-pointer

dial. Simultaneously, the latter is switched to display the relative position of the terminal angle beam selected, and the horizontal pointer moves to the bottom of the dial.

The pilot pulls back on the stick to centre the horizontal pointer and manoeuvres to keep it centred, causing the aircraft to fly a flareout path. The point on the runway at which touchdown occurs depends on the terminal glide angle selected and on the height of the aircraft antenna above the base of the wheels.

The Airborne Instrument Laboratory originally conceived the system as a replacement for ILS, known as EAGLE (Elevation Angle Guidance Landing Equipment), but considering the extent of investments all over the world in existing ILS equipments, and the consequent unlikelihood of having a replacement adopted, it was decided to limit the new system and make it a complement to existing installations.

Another advantage brought out by the manufacturer is the possibility the system affords of being checked before each approach, since the FILS beams extend out for up to 20 miles and the pilot can, for example, measure the relative angles for the regular ILS glide slope beam and one of the FILS beams as his aircraft passes the outer marker.

FILS is also free of the terrain problems which beset flareout systems in which an airborne radio altimeter is used to measure aircraft height above the ground. These require flat terrain on the path to the instrument runway, whereas FILS is independent of terrain.

FILS could be used as a helicopter approach aid, its 0-20~ sweep permitting a much steeper approach than the low ILS beam.

Flight testing of the FILS system has been conducted by AIL in co-operation with the Eclipse-Pioneer Division of Bendix Aviation, who provided a specially instrumented B-25 aircraft (which has also been used for flight tests of the Gilfillan REGAL all-weather landing system. Bendix holds an FAA contract to develop a flareout coupler for REGAL, and is negotiating a similar contract with the FAA for an automatic flareout for FILS).

AIL has received FAA contracts covering static tests on FILS beam flatness and accuracy and for installation of a second FILS at the FAA's Atlantic City test centre.

(ITA)

Phil Geraci

Sweeping changes in the airways pattern ove~ ma~y oreas of the nation, a new form of flight rule which will permit pilots without instrument ratings to op~rate under ATC control; and a steady increase in automation for both record-keeping and air route surveillance - these were some of the points of the long-awaited Pro~ect Beacon Report on Safe and Efficient Utilization of Airspace.

For business aviation, by far the most significant departures from the existing system will be changes which Rpp路 q1tecl 路.vllh ::1ncl pe1 m1ss1on of SKY 1NA YS. December 1961

'.?6

are due in the airways pattern. The 138-page document states early that: "Most serious problem is the mixture of IFR and VFR traffic along the high-use airways, particularly in view of the high speed of many aircraft."

As a guide to remedial measures, the report goes on to postulate "a recommended air traffic control system" which provides for maximum separation not only between I FR and VFR aircraft but also between aircraft of differing performance characteristics. Here, in the words of the Project Beacon task force, are the primary recommendations:

Beacon Recommendations

Control should be based on aircraft position information continuously available on the ground and independent of the pilot's navigational information.

On certain high-use airways and in congested terminal areas, controlled and uncontrolled traffic should be segregated and speed limits instituted for VFR traffic.

All traffic above mountainous areas MSL in the rest of control. On certain requirement should

24 OOO ft. MSL in and adjacent to high of the country and above 14 OOO ft. the country should be under positive high-use airways, the positive control be extended down to 8 OOO ft. MSL.

To enable the non-instrument rated pilot to use these positive control areas under VFR conditions, a new category of flight should be established. This might be known as Controlled Visual Rules (CVR). Under these rules the pilot would enter the traffic control system and receive separation service but would maintain aircraft attitude by reference to the ground.

Below 8 OOO ft. MSL on the high-use airways referred to above, a speed limit should be established for all traffic.

All aircraft above 12 500 lbs. gross weight should be required to carry altitude reporting beacon transponders for use both en route and in terminal areas.

The combined SAGE/FAA radar network should be employed for en route control and, along with flight plans, provide the basic control information.

In the congested terminal areas aircraft should be segregated in accordance with performance and special arrival and departure corridors designated.

All aircraft landing at controlled airports within these designated terminal areas should be required to contact approach control at a specified distance from the airport.

Altitude information should be obtained through the use of altitude reporting beacon transponders carried in the aircraft. Task force studies indicate that a short-range beacon satisfactory for terminal area use should be obtainable for no more than S 500. When such a beacon becomes available, it should be required in all aircraft landing at controlled airports within the designated congested terminal areas.

Special corridors and tunnels should be provided for unequipped VFR aircraft landing at uncontrolled airports or transiting the terminal area.

With complete position information available on the ground, pilot reports should be reduced drastically and controllers and pilot load and frequency usage therefore held to reasonable levels.

General purpose computers should be employed in both the enroute and terminal area portions of the system to process flight plans, issue clearances, make conflict probes, generate display information, establish landing sequences and perform other routine tasks of assistance to the control function.

Special express routes must be established in terminal areas to accommodate the greatly increased helicopter traffic envisioned in the near future.

The report estimated that a capital expenditure of S 500 million, exactly twice the current FAA five-year plan, will be required, but noted that the present FAA Research and Development budget of S 65 million annually should be adequate.

The report proposed that aircraft entering terminal areas be segregated according to performance in an "offairways structure" consisting of an approach control area extending outward for 25 miles at medium altitudes and outward to 50 miles for higher altitudes. Into and out of this approach control area aircraft would be funneled along different paths".

The jet corridor would be aligned with the ILS runway, to accomodate the jet's lack of maneuverability. Corridor No. 2 would encompass "intermediate" aircraft such as the Electra and DC-6. Corridor N. 3 would be reserved for low-altitude, low-performance aircraft which, because of greater maneuverability, could quickly be worked into the landing pattern by the local controller.

This concept would abandon the present "downwind leg, base leg and final approach" pattern in favour of a system which would end the necessity for any aircraft to cross the ILS approach path. Aimed only at high-density airports, such a plan would leave to the individual airport the working features which would be tailored to specific requirements.

All-weather Landing

The report urged continued efforts toward all-weather landing systems, but stressed that the "long-term effort toward an integrated all-weather final approach, flare and landing system with allweather takeoff capability" should be "evolutionary" in nature.

Collision avoidance received little encouragement, although the report urged continued work in this area.

Implementation of the "Runway Visual Range" concept in defining runway conditions was strongly urged by the Beacon Task Force as a boost to takeoff and landing efficiency. The report also ea lied for more upper air reports, for more automatic equipment for weather reporting, and for a study of Weather Bureau, FAA, and military weather services with an eye toward greater coordination and less duplication.

Civil airports were called "noteworthy for their lack of consistency of design and standardization", due to variation in Federal, state and local ownership. ,, No immediate timetable other than the "five year goal for the total system was given in the Beacon report. B.ut . . o tee h n1cal advisory board under Beacon t as k force cha1r. 路 d to carry out man Richard R. Hough has been organize d . P .d ntial man ate FAA Administrator Najeeb Halaby s resi e . . nd the Pro1ect to fashion an air traffic control system a1 ou Beacon blueprint.

Prof. Dr. H. von Diringshofen

The Importance of the so-called "Human Factor" for the Reliability of Collision Prevention in the Terminal Area As long as there is no automatically operating and sufficiently reliable instrument system for preventing aircraft collisions, the avoidance of such accidents is dependent on the following human factors in flight safety: I. 0 n Bo a r d, on the ability of the pilot when flying under visual flight rules to evade other aircraft in time.

II. 0 n the ground, on the ability of air traffic control to provide for the necessary safety separation in the airspace under control.

Neither of these is possible at the present time with the requisite reliability.

In many aircraft, pilots have a very restricted field of vision. They cannot continuously search the airspace for other aircraft because they have a great deal more to do, particularly after take-off and when approaching an airfield for landing. Thus there occur frequent intervals in the observation of the airspace, in which, under certain circumstances, other aircraft may approach unnoticed within a critical distance on a collision course.

In practice these intervals are often considerably longer than necessary. It is a problem of training in flight discipline, to keep them as short as possible.

But even with the best intentions on the part of the pilot, these intervals cannot be reduced to less than 10 seconds in most cases. This can have critical consequences, particularly in the terminal areas of airports with their large numbers of aircraft in flight, even when the approach speeds are low.

In this connection, an article by A. Zeller in the periodical "Aerospace Medicine", from the viewpoint of "Man when anticipating collisions in the air", is very informative.

According to this article, 33 such collisions occured in the United States in 1958.

Of these, 80% were within a radius of 30 miles of airports, mostly under visual weather conditions, at moderate speed. In half of these accidents the cause was: other aircraft not seen; in 25% faulty estimation of distance and in some 20%, too late or wrong evading action.

It would thus be unrealistic to believe that pilots, when flying under visual flight rul~s_, constantly watch the a_irspace so effectively, that coll1s1ons ~an be preve_n!ed with requisite reliability. As a result, satisfactory coll1s1on prevention is at the present time only possible by means of air traffic control from the ground. This is supported by the very small number of aircraft collisions under weather conditions that only make flying possible under instrument flight rules.

Unfortunately present day technical means _and ~t~tu足 tory conditions are invariably inadequ~te for _identifying and determining the altitude of every aircraft in the controlled airspace and to pass the necessary information t_o its pilot through the medium of radio telephony._ For t~1s reason the radar controllers can only inform the pilots with whom they me in communication about non-identified air-

28

craft when their flight path might be a collision course. As such warnings are given much more frequently with the altitude data missing than should otherwise be necessary, and as the pilot notified can often not see the aircraft in question, because it is far off at a different altitude, these warnings cause anxiety and finally induce non-observance.

In the Air Traffic Control profession it is a natural tendency for the controller to deem himself largely responsible for protection against collisions in the airspace he controls. He therefore experiences the collision situation that he has not sufficiently clarified, because of non-identification of aircraft on radar, as a considerable psychological burden, which often weighs more heavily than the strain of controlling densely crowded airspaces, in which controlled !FR-flights are operating. The extensive use of radio-telephony equipment in private and sports aircraft, and the introduction of secondary radar with automatic data transmission systems for identification, flying altitude and speed, could certainly improve the reliability of collision prevention in terminal areas and notably relieve the controller. Radar installations operating threedimensionally and an automatic proximity-warning from the ground are most desirable but are only to be expected in a distant future.

There are not many professions, in which the sense of responsibility for the lives of others is generally so highly developed, as in the Air Traffic Controller's profession.

At the present time air traffic controllers work at the focus of air traffic, often up to the limit of the strain they are capable of supporting, for reliable accomplishment, pressed for time as they are and under the pressure of great responsibility.

They are aware of the present technical inadequacy of their air traffic control system which can still not be avoided and experience fairly often near-collisions which occasionally only have a happy outcome through favourable luck. They often have to disentangle critical air traffic situations which demand the greatest concentration and rapid decisions. The life of more than 100 people may depend on whether the air traffic controller is fully efficient or whether he is restricted in the accuracy and speed of his actions by fatigue or some other deterioration of his state and his strength of vision.

Under heavy stress on the air traffic-control staff, which is becoming ever greater and of longer duration as a result of the increase in density of air traffic at its focal points, human reserves of capacity for work are so small that every reduction in capability because of the inade~ quacy of the environmental conditions, such as unsuitable lighting, insufficient air conditioning, too high a noise level, uncomfortable seating and many other things as well, may under certain circumstances have dangerous results, particularly if the staff position should make more than two hours of uninterrupted attention necessary under full strain. In this connection, air traffic controllers in the conventional control are particularly liable to disturbance,

because their task demands powers of memory and imagination which are very easily affected unfavourably by fatigue. It is by no means infrequent for radar controllers to note errors in the conventional control, which may result in the circumstances in a dangerous proximity of the aircraft.

Aircraft cannot pull up short whilst in flight. They can only temporarily and in restricted numbers be confined to a holding pattern. This is the fundamental difference between the system of air traffic control and the control of road, rail and sea traffic.

Air traffic controllers form part of a very rapidly operating man/machine systeme in which human and technical factors of flight safety, both on the ground and in the air, comprise a functional unit. In this system the human factor in air traffic control, with regard to preventing collisions in controlled airspace has become just as important as the pilot.

Because of the close functional link between pilot and controller, it appears to be advisable, with a view to improving flight safety, that the latter should often be given the opportunity of flying with the pilot in the cockpit of commercial aircraft, in order to acquaint himself with the problems met with on board. Again, flying training for controllers, as it is carried out in Belgium, France and Austria, with official facilities, appears to be thoroughly logical. Pilots, too, should in their own interests, take the trouble to get an insight into the problems of air traffic control and an appreciation of the limits of efficiency of this system.

In the coming years, demands on air traffic control staff, and especially on controllers, will certainly increase considerably because during this period the growth of air traffic will presumably be substantially quicker than the relief afforded to the ATC staff by new technical methods and automation. This gives rise to the urgent requirement to exhaust every possibility for technical improvements which can reduce the strain on the staff, even in the smallest details, and to spare no measures or expense in the process. Such anthropotechnical rationalisation, as well as physical and psychological operational hygiene, belong to the crucial part of the flight safety program.

For this purpose, the engagement of an industrial doctor with good physiological and psychological ability and experience and with a particularly sympathetic understanding of the importance of air traffic control, is indispensable. Only a doctor of this type has a sufficient! trained abilit~ for re:ognising and correctly assessing ~ lack of ~perat1ng hyg'.ene and the capacity for making the most suitable suggestions for its elimination. However he will need to collaborate closely with a suitable technic ian.

Without an industrial doctor, ATC is not only a curiosity, but also evidence that authorities concerned who do not wish to sanction the cost of such a doctor, fail to recognise the importance of the human factor in ATC with regard to flight safety.

1

The fact that the number of collisions of commercial aircraft still remains very low, does not justify the assumption that this will be so in the future, unless steps are taken in all large ATC-centres to see that the air traffic controllers, employed there only after rigorous checks on their suitability and proficiency, are given optimum terms

of employment and are in a psycho-physical state that guarantees their full efficiency.

Such a requirement has long been a matter of course for pilots of commercial and military aircraft. The medical supervision of the operating conditions in air traffic control and of air traffic controllers should be just as much a matter of course. Here special observation must be directed to the appearence of nervous symptoms and the indications of overfatigue, because these point to a considerable reduced speed and accuracy of observation and action. In these cases prompt measures for relaxation can generally completely and fairly quickly re-establish full efficiency and ability to stand the strain.

Nervous supervisors are particularly unsuitable in air traffic control work, because of their harmful effect on the mental operating atmosphere. Candidates with evident symptoms of nervous and psychological instability should not be put to work in air traffic control, even though as a result, candidates may be lost who might become sufficiently stable with increasing age.

It would be very regrettable if the full importance of the human factor in air traffic control, as regards the reliability of collision- prevention, would only then be generally realized, if demonstrated unambiguously by a series of collisions in the air with many deaths, attributable to human failure of air traffic controllers as a result of overstrain.

In the coming years the probability of such demonstrations may occur much more often, if air traffic controllers find themselves increasingly pressed for time by the rising density of the traffic, that is, if the available time becomes less than is essential for the reliable accomplishm~nt of their work. Then their capabilities will fall rapidly with the quotient: time available I time required, in the form of a quickly steepening curve. The time required by h~man beings for a quite simple, reliable action does not differ greatly individually and according to conditions.

For correctly appreciating and mastering a complicated situation however, the differences in the time needed are very great, as these are governed by individual ability and th~ temporary physical and psychological frame of mind.

It is for this reason that, when time is short, the reliability 0 ~ collision prevention through air traffic control is so highly dependent on the professional ability and healthy frame of mind of the traffic controllers as well as on V:hether they are in a vigorous state or exhausted at the time.

Only automation can provide sufficient reserves of time in ATC as it is increasingly withdrawing the human factor from direct inclusion in the functional chain of this system.

But there is still a long way to go to achieve this goal.

Such complicated technical systems can, however, only operate with adequate reliability, if they are constantly supervised and maintained by human bAings and if provision is made for man to make the necessary compen sation promptly by means of other technical methods in emergencies.

The physical and psycho-physical adaptability of man to aeronautical technical science has its limits. The odaptability of technical science to man, however, 1s pract1 cally unlimited. It is therefore a much better prospect to adapt technical science to the shortcomings of rnon. them to occustom man to the shortcomings of science.

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ITA contd. from page 18

ITA's Activities ITA's activity takes several forms. In addition to the periodical publications which are normally supplied to all Members, special research work is undertaken and expert advice is given upon demand.

ITA's "Consultant" capacity. A group of full-time specialists constitutes an international centre of research on aviation and other means of transport to which a Member or group of Members refer their specific problems for thorough study and expert advice. The studies thus prepared upon demand-on a contract basis-are restricted to the exclusive use of the requesting Member or Members.

They may take several months of preparation and entail thorough on-the-spot enquiries.

Furthermore, the specialists who have prepared a special study continue to keep the matter under review and are at the disposal of the Member to discuss conclusions and practical steps to be taken.

This function is considered to be of the greatest importance. It is developing every year. As a consultant, the Association has the satisfaction of making a contribution towards the solution of important problems put to it directly by its Members.

The "Reference" and Advisory Service", another much appreciated function, is at the disposal of Members to answer their more current enquiries.

In addition to everyday information, loan of publications etc., IT A draws up advisory reports or flies at short notice.

They may take the form of a short communication on the particular point raised or of an annotated bibliography.

This kind of rapid service saves the requesting Member a good deal of time and research. It is free of charge for Full Members, within certain limits.

In addition to these two types of "personalized" service membership of ITA automatically implies the right to receive the periodical publications of the Institute.

These include the English and French editions of: ITA Research Papers Information Papers ITA Bulletin "ITA Research Papers" are published at irregular intervals but at the rate of about one a month. They vary in size from 20 to 150 pages. R.P.s are prepared by members of the staff and require several months of work. Subjects are chosen either according to wishes expressed at the General Meetings or during interviews with Members, or on management initiative.

Research Papers constitute one of the most original and valuable aspects of ITA's work. They aim at a thorough investigation of the main issues in the economic, technical or other flelds of air transport.

"Information Papers" appear 6 or 10 times a year. They are intended to make sure that data from other sources on matters of particular interest will not escape the attention of Members. Unlike Research Papers, they do not constitute entirely original work by IT A. Each Information Paper has from 15 to 60 pages often illustrated with graphs or maps.

"ITA Bulletin" is published weekly, except during August.

There ore about 20 pages to the issue, with graphs or mops where called for. The complete series for each year

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runs to about 1000 pages made up of original articles or analytical comments varying in length from 2 to 6 pages, short notes, book reviews. etc.

ITA Bulletin's aim is to enable its readers to follow the problems and development of air transport, the aeronautical industry and air work throughout the world as efficiently as possible.

ITA's Members ITA Members not only include Civil Aviation Administrations and Departments, but also Departments of Foreign Affairs, Economic Affairs, Merchant Marine authorities local Governments in overseas territories, etc.; very nume~ rous air transport companies and the majority of aircraft construction firms of the world; railway, shipping and road transport companies and associations, national or international; airport operators; passenger and freight agents· oil companies; insurance companies; research organisa: tions, Universities and Chambers of Commerce interested in the legal or economic aspects of air transport.

End of 1960, ITA Members included, inter alia: 30 Governments represented by their Civil Aviation Administration 38 air transport and air work companies in 27 countries

15 organisations or firms representing surface means of transport

41 aircraft constructors, equipment manufacturers and establishments for servicing, maintenance, overhaul and modification of civil aircraft (in Belgium, France, Italy, Netherlands, Sweden, United Kingdom, United States) 32 Universities, High Schools, Institutes and L.b · · A .

1 ranes . A ( in rgentina, ustna, Belgium Brazil Canad F . ' , a, ranee and Algeria, Germany, Italy, Spain, Turkey, United States, U.S.S.R., Yugoslavia) In addition, 15 international organisatio ns * ma d e regu Iar , use of IT As work and participated 1 ·n 1 ·t s ac t.1v1·t·1es.

Conversely, ITA attends various intern a t.1ona 1 con f erences, as observer or expert.

It may seem surprising that such a w·d · t y o f ·in.

1 e vane terests should find 1t useful to 1·oin ITA , th e more so t h at a good already belo ng t o o th er ·inter. number of. Members . national organ1sat1ons. dealing also w1'th air · t ransport . matters. But · · I points · . - and this 1s another of th e ongina o f ITA - 1t should be remembered that th th . · I · · · e o er 1nternationa institutions concerned are eithe r spec1a · 1·1zing · ·in . very definite .aspects of air transport or are ·in t ereste d ·in . · 1t only occasionally, whereas ITA - in 'its own sp h ere . does not duplicate any of these institution s, ·t · b eing · 1 s aim on t h e contrary to help and to complement th F h IT A · · . em. urt ermore,. . is unique in that it is the only international organisation whose Membership is open to II h h · ffr · . a , w et er engage d in o 1c1al or private activities.

ITA is organised and works in ways that d'is t'ingu1s · h ·1t from any other body. .It can adapt its worki'ng . programme to frt . closely the ma1or interests of ai·r t ranspor t , w h'I1 e . remaining free to pay attention to individual Member requirements. · These included: FAO, IATA, !CAO. etc.

1962 Annual Conference of the International Federation of Air Traffic Controllers Associations to be held at Paris-Orly The 1962 Annual Conference of IFATCA will be held in Paris-Orly, April 25th to 27th, 1962. The French "Association Professionelle de la Circulation Aerienne" will be host to the Conference and is at present endeavouring to arrange an exposition of air traffic control equipment, which should take place at the same time.

Air Traffic Control delegates of more than 30 nations as well as observers from other international aviation organizations, from national aviation departments, and from military aviation agencies will be invited.

Preliminary prog.-am of the Conference:

Wednesday, 25th April, 1962 14.00 Meeting of the Elective Officers of the Federation 18.00 Informal meeting of all participants with cocktail party

Thursday, 26th April, 1962 08.30 12.30 14.00 18.00

Annual Conference of the IFATCA Directors Lunch Annual Conference continued Adjournment

Friday, 27th April, 1962 Visit of Orly Airport - Decca Demonstration Flights Lectures and/or ATC Exposition 18.00 Meeting of Elective Officers The following preliminary agenda has been proposed for the official Conference:

1. Call to order by Secretary 2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

Roll-Call of Directors by Secretary Opening of the Conference by the President Welcome to Guests, Observers, and Directors Correspondence and applications for membership Presentation of report of previous Conference Reports of Officers Report of Auditor and Budget 1962 Reports on establishment of Standing Committees Composition of Standing Committtees Federation policy Co-operation with other organizations Nomination and election of Scrutineers and Tellers Nomination and election of Officers Miscellaneous Adjournment

Great Problems in Air Traffic Control From November 23rd to November 24th, the German Air Traffic Controllers Association held its 1961 Annual Conference in Nurnberg, Germany. The following resolutions concerning critical problems of the Air Navigation Services were passed by delegates from Air Traffic Services units at all German airports.

Whereas, the rapid increase of civil and military traffic in recent years and the growing density of private sports- and cross-country-flights have caused great difficulties for Air Traffic Control, and Whereas, the forthcoming introduction of civil Mach 2 transport aircraft will even more affect the safety of Air Navigation, Now therefore, the following requirements were considered indispensible for the maintenance of safe and orderly systems of Air Traffic Control.

1. A more intensive integration of civil and military air traffic control services in order to guarantee the expeditious and orderly flow of all air traffic. For this purpose, the control of all military flights, except those in the very vicinity of military air bases, shall gradually be transferred to civil air traffic control units, because military en-route flights and their approach and departure procedures are inseparably interlaced with civil traffic and, therefore, can not be controlled independently.

2. An immediate step-by-step extension of controlled airspace up to an altitude of 40 OOO feet in order to achieve positive control of civil and military jet traffic, which is at present flying uncontrolled and is only provided with Flight Information Service.

3. All power-driven aircraft shall be equipped with radio sets of adequate technical quality, if necessary with financial support by the government. Thus a continuous two-way radio communication with ground units can be maintained, such a communication being the prerequisite for the control of this traffic if required.

4. Experimental introduction of positive control of all air movements in a limited portion of air space of the Federal Republic to gather experience in the control of VFR flights within congested areas.

5. To increase the safety of flight operations, control towers shall be established at certain private airfields which are highly frequented or critically located in the vicinity of controlled airfields.

The aviation public was called upon to support air traffic authorities in the implementation of this program which is bound to increase safety in air navigation and t~ protect the public from avoidable dangers. It is particularly necessary to provide the competent aviation authorities with adequate financial means so that better _technieetl equipment and facilities can be installed and highly . d 路 sufficient numbers qualified personnel can be ernp 1oye in to ensure efficient operation.

The rob Iem of how to avoid accidents in priva_te sports p 路 d. sed by a working comand cross-country flying was 1scus . mittee of the German Air Traffic Controllers Assoc1ot1on.

The result of these investigations and the resolutions adopted ot the Nurnberg Annual Conference wi II be passed to the appropi路iate Federal Air Nov1gat1on Autho rities.

31

Survey:

Modern Equipment, Installations and Systems for Air Traffic Control and Air Navigation

Contents

I AJ( I

Air Traffic Control EUROCONTROL Association tests HARCO System Air Traffic Control Proposals by STC and European Associates to the EUROCONTROL Association

I RADAR I

EUROCONTROL

Communications Notch Aerial Tuning Unit for Aircraft Use

NAY

Navigation Universal Doppler Navigator Ryanav IV

Radar Equipment and Systems "Tiny Tim" for In-flight IFF and ATC Testing New X-Band Parametric Amplifier

[[!I]

COM

MET

Meterorology Facsimile Weather Map

will test HARCO System

The EUROCONTROL Association will investigate the possibilities of the HARCO (Hyperbolic ARrea COverage) System. HARCO is a low frequency navigation system which operates similar to Decca, with hyperbolic position lines. Recently the EUROCONTROL Association expressed an opinion to the effect that, although VOR/DME will have to be used during the next years to come, it may be necessary to implement a new or an improved navigation system.

Preliminary specifications for such a system have been worked out by EUROCONTROL and were distributed to

all major European electronic firms early last year.

The Decca Navigator Company, England, together with CSF, France, and Telefunken, Germany, submitted a development proposal which meets the EUROCONTROL requirements. The new HARCO system is an outcome of the joint development by these three firms.

Part of the evaluation program will be an extensive flight check. Slight modifications of one Decca chain are necessary to carry out this program.

(Telefunken GmbH)

Air Traffic Control Proposals by STC and European Associates to the EUROCONTROL Association Detailed proposals for a navigational system for the control of upper air space have been submitted to the EUROCONTROL Association jointly by Standard Telephones and Cables Limited, London, and its major associated manufacturing Companies in Europe, Le Materiel Telephonique (LMT), Paris, and Standard Elektrik Lorenz (SEL) of Stuttgart. The proposals have the backing of the Bell Telephone Manufacturing Company, Antwerp, and Nederlanclsche Standard Electric Maatschappij, N. V., of The Hague. both also STC associates.

The EUROCONTROL Association has asked for technical proposals for o novigation system to meet the re-

32

quirement of_ its provisional specification of April Sth

1961, and wh1c h could be operational by 1965.

I

The STC/LMT/SEL Proposals A thorough investigation of the possibilities has been carried out by these three Companies which between them hold a large number of patents on radio aids to navigation, and have b~en primarily concerned with the development of the radio compass; ILS (Instrument Landing S _ stem); VOR (VHF Omnidirectional Radio range).

(Distance Measuring Equipment); and TA CAN (Tac;ial Air Control and Navigation System).

oJ'E

Since the system in most common use is VOR/DME, sta ndardised by the International Civ il Aviation Organisation in April 1960, and scheduled to be install ed throughout Europe, it was o f prime importance to consider whether this system cou ld be adapted to meet the EUROCONTROL speci ficat ion.

STC/ LMT/ SEL state the following in their proposal: " A study of the fundamentals o f all navigat ional systems for upper oir space control shows that the accurocy and area coverage are inter-dependent, th e accuracy limiting th e coverage.

Th e DME portion of the VOR/ DME sys tem wi ll, in 950/o of ca ses, give a distance accuracy better than that demanded by the EUROCONTROL Association (Âą1.5 naut. miles) where the range is limited to 200 n. m. from the station. In fact, in its present form, the DME could meet this accuracy up to 700 n. m.

The VOR portio n w ou ld require improvement and it is pro posed that techniques evo lved by STC in connection w ith a modified VOR, known os VORAC and satisfactorily evaluated in 1957, togethe r with those evolved by SEL in connection with o wide-apert ure Doppler direction finder shou ld be combined lo produce an improved VOR. (A small additional unit is required in the aircraft to take full advantage of the increased instrumenta l and performance accuracy a va ilable from the improved VOR). This improved sys tem is referred to in t he proposal as VO RDA C (VH F Omnidirectional Range/Di stance M easur in g Equ ipment for Area Coverag e)."

In the opinion of the Companies, VORDAC wil l fully meet th e r equirements for Air Traff ic Control outl ined in the EUROCONTROL specifi cat io n and could be opera tional by 1965.

The system thus con sists of a standard !CAO DME and the improved accuracy VOR. The present VOR receivers a re fu lly compatib le with VO RDAC (about 100,000 are in current use), giving the present instrumental accuracies w hen used without the additional unit. The use of this system permits th e estab l ishment of aircraft position information in polar co-ordinates similar to t hose currently supplied by rada r and incorporated in present ground contro l systems.

Extensions to the VORDAC System

It is proposed by the companies that a simple, cheap and lightweight track computer should be installed in each aircraft. A form of pictoria l disp lay has al r eady been developed for ai rbo rne navigation. This display contains pictoria l maps w hich can be qu ickly changed without any re-setting procedu re os the aircraf t progresses from one VOR beacon to a nother .

An appendix to the proposals detail s o method of feeding navigationa l information from the a ircra ft to the gro und con tro l ler. This system is known as Dataramo and can make use of the normal VHF commun ication channel with additional coder/ decoder equipment.

(Standard Telepho nes and Cables Lim iled , London, W. C. 2)

"Tiny Tim" for in-flight IFF and ATC testing " Tiny Tim ", a go, no-go test set for in-flight and preflight testi ng of IFF tran sponders and ATC beacons has bee n deve loped by H aze ltine Corporatio n, Little Neck, New York.

Small, compact and light weight, th e transistorized device can be carried in any type of aircraft for interrogo -

lion in modes 1, 2 or 3/ A and for monitoring the reply .

Complete ly independent of ground eq uipment, " Tiny Tim " prov ides go, no- go information on the basis o f rece iver sens itivity and frequency, t ransmi tter power a nd frequency, coder and decoder operations and antenna match.

(Hozelline Corporolion, Liltle Neck , New York)

Tiny Tim Tesler

33

~

~

New X-Band Parametric Amplifier

Texas Instruments new nondegenerote X-bond porometric amplifier feo tures single-knob tuning to simplify operation.

Single-knob tun ing over a 1.1-GC range provi des operational simplicity in a new nondegenerate X- band parametric amplifier deve loped a t Texas Instr uments. Intended primari ly for radar app licati ons, the amplifier can be used to extend the rang e of existing radar equipment o r incorpo rated in adv anced after designs. Im portant performance features a re a 4.5-db system noise figure, including circulator loss and normal second stage contribution ; 30-mc bandwidth at 15-db gain, and a fixed K-ba nd pum p frequency with less than 50 milliwa tts o f p ump powe r required. The amplifier uti lizes a sing le TI gal lium arse nide varactor diode in a broadband circuit that gives stable gain characteristics and requ ires minimum tuning adj ustment.

(Texa s Instruments, Dallas, Texa s)

Notch Aeri al Tuning Unit for Aircraft Use The ever present dema nd for improved performa nce in modern aircraft has made the preservation of aerodynamically clean su rfaces increasing ly important. Projecting HF aerials can be eliminated by using, as a radiator, a notch let into part of the aircraft st ructure, the aerodynamic shape being preserved by the use of dielectr ic materi al. Th is notch may then be tuned to th e required frequency and matched to the outp ut of the transmitter by an Aerial Tun ing Un it.

The Aeronautical Division of the Marconi Compa ny hove desi gned a tuning unit for the HF notch aerial in the Vickers VCl 0 aircraft, under contract to Vicke rs-Armstrongs (Aircraft) Ltd. Thi s unit w ill be standard equipment in all aircraft of this typ e a nd it is a lso sui table for the de Hovi llond Tr ident, and for any oth er ai rcraft where a notch of suitable dimensions con be prov ided. It con be used w ith any transmitte r conformin g to the latest ARINC specification for HF air-to -gro und communications systems, and with other tra nsm itters of earlier design.

In this unit, the ph ase and magnitude of the RF output to the ae r ial and the RF input from the tran sm itter ore continuously compared by means of discriminator circuits .

These discriminators co nt ro l variable reoctonces in the aerial matching network and automatically drive them to a position where th e input an d output are in pha se and the notch aeri a l is matched to the transmitter at the rad iated frequency.

With the exception of the main 400 c/s relay, so lid sta te switching is used throughout, and all servo-am p lifiers an d choppers ore fully transistorised . The whole unit is contained in a pressurised cylinder to ens ure p eak performance under all environmenta l condition s and a pressure sensing switch is incorporated to detect any leaks from

Tempera tur e Range : A ltitude: Powe r Requirement :

D imensions: W eight :

the pressurised container.

Data Summary : 2 - 24.999 Meis 1OOO watts peak, provided mean power does not exceed 200 watts 52 oh ms Input Impedance: Not greater than 1.3 to 1 V. S.W. R.: Notch Inductance Limits : 1.1 to 1.3 M icro-henries Not greater than l 0 seco nds Tuning Time :

Frequency Range : Power Rating :

34

oo c

- 55째 C to + 1 0 Up to 60,000 feet 27.5 V DC Normal 1.3 A Tuning 2.5 A (7.5 A peak) 115 V AC 130 mA Length 22 in (56 cm) approx.

Ma x. D iam. 7 in (18 cm) 20 lb (9 kg)

Notch Aerial Tuning Unit Type 7400

Universal Doppler Navigator Ryanav IV

For use in all types of air vehicles, including fixed-wing aircraft, helicopters, V/STOL aircraft, and drones Ryan Electronics have developed new Doppler navigation equipment: The Ryanav IV. It is designed to accomodate the speed ranges between minus 50 and plus 2000 knots, altitudes from zero to 70 OOO feet, drift velocities from zero to plus or minus 300 knots, ground track from zero to 360 degrees, and vertical velocities to 60 OOO feet per mi nute.

"The accuracy of the Ryanav IV is excellent, and being improved steadily. Velocity error is in th e order of '/• per cent. Navigation positional e rror is in the order of 1h to 1 pe r cent of distance traveled. The hovering threshhold is 'I• knot. The use of pure continuous-wave (CW) Doppler techniques makes it poss ible to achieve th is accuracy without altitude or attitude "holes" from take-off to landing", says Ryan .

Ryan is of the opinion that th e CW techn ique is the most suitable to accomodate the positive, negative, and

zero speed domains, the near-zero altitude requi remen ts of helicopters and V/STOL vehicles, and the high altitude requirements of modern jets.

The Ryanav IV antenna directs continuous-wave energy towards the earth's surface at a frequency of 133 OOO Meis in three narrow beams. The frequency o f the energy backscattered form the earth is " Dopp ler sh ifted" by an amount proportional to the aircraft's velocity a long each ind ividual beam. The three Dopp le r frequencies are measured and used to compute the aircraft's velocity components.

This is accomplished in the converter/ computer unit which comprises a low voltage power supply, a frequency tracker module, o frequency converter/velocity computer modu le, and a navigation computer module.

From computations performed o n the th ree Dopp ler frequencies, electrica l outputs of head ing velocity, dr ift velocity, vertical ve locity, ground speed, ground track, drift angle, true head ing, wind speed, and wi nd head ing ore provided, as we ll as east-west and no rth-south di stances troveled.

RECEIVER·TRANSMITTER CONVERTER/ COMPUTER

DIRECTION VELOCITY INDICATOR

CONTROL INDICATOR

GROUND/ WIND VELOCITY INDICATOR

35

NAY

In turn all information is transmitted to di splay instruments. These visua l displays include a Control Indicator, a Ground/Wind velocity Indicator, and a Hovering Indicator.

The Control Indicator has three functions: 1. Cont rol of the entire navigation system, 2. Control of the Ground/Wind Velocity Indicator, 3. Provision for setting in magnetic variation.

Th e Control Indicator governs the system mode of operation from five switch positions at upper left : Off, Standby, Land, Seo, and Test. Th e knob at upper right is used to set in magnetic va riation. This information is incorporated automatically into the systems navigational computations. The three togg le sw itches below contro l the Ground/Wind Velocity Indicator. The switch at right permits the pilot to select readings of wind speed and w ind heading or ground speed and ground track. Th e other two switches con be used to electrically sl ew the pointers on the Ground/Wind Velocity Indicator, numerically increasing or decreasing t he readings o f wind force and dir ection in the event that the operator desires to overr id e the Doppler-derived data.

Facsimile Weather Map New four-foot weather mops now make possible the briefing of large groups of up to 50 people simultaneously, an advantage of si gnificant importance for rap id briefing of military personnel and commercial airline pi lots, where weather plays a key role in hour to hour planning.

According to the manufacturer, Alden Electronic & Impulse Recording Equipment Co. of Westboro, Massachusetts, facsimi le equipment presently used produces weather maps 18 inches in w i d th which ore su itable for weather station and individua l pil ot b ri efings.

Th e Hovering Indicator con sis ts of crossed horizontal and vertical bars, with a pointer on the left side of the instrument face. The horizontal bar shows fore and aft velocity, the vertical ba r shows drift velocity, and the pointer at left indicates vertical velocity. When a ll are center ed th e aircraft is in a hove r.

Th e G rou nd/Win d Veloci ty Indicator is a two-in -one di splay. It is operated from t he C ontrol Indicator to read out ea ther grou nd speed and ground track or wind speed and wind heading. The Ground/Wind Velo city Indicator can be switched from one mode to the oth er mode as needed. Ground speed or wind speed is indicated on the inner dial in knots. Ground track or w ind heading is read on the outer dial in degrees. Th e inner d ial is stationary with a revolving pointer, but the outer dial revolves aga inst a fixed index. Indicator lights b elow the dia ls show the mode fo r opera tion: Ground, Wind, or Off. Th e receiver-transmi tter in the Ryanav IV employs a space- duplexed, fi xe d antenna w hi ch has no moving parts an d re quires no adjustment. The combination of fixed an tenna a nd a ll -attitude dote -stab ilizing computer is claimed by Ryon to provid e a cc urate outputs over an ext reme ly w id e range of aircraft pitch, rol l, and drift a ngles. Supersonic speeds may be accomodoted by shifting t he receiver freq uency band. No cha ng e in antenna a ng les or other system parameters is necessary.

In addition to pr ovid ing outputs for tie-in w ith pl otting boa rds and o th er position indicating equip ment, the Ryanav IV"s o utp uts may also be used to d rive co urse and distance compu ting and indicating equipment, co ntrol inertial navigation eq uipment, bo mb director sets, ASW sets, and terrain clea rance radar.

Plug -modular des ign provides a w ide rang e of output options without modifying the basic d esig n. Antennas con be pr ovided to meet specia l ized structural or operational requirements.

Th e set a l so incorporate s provisions for se l f-co ntain ed functiona l and ca l ibration tests . A system test set , and a tes t bench harness si mplify checkout.

(Ryan Electron ics, San Diego, Cal ifarn ia)

36

Giant four-foot wide "bulleti n" weather maps can now be produced directly from the regular U . S. w ea ther map tran smission network .

R路.i.nc- Ul .,.icr Heim

61 , rte de ._atecuin e ;; r i n

GE

In der Luftstrassenuberwacnung una -

路

Oberall wo Leistungsfahig.kelt/ ._____ ....,. .....

Nah bereich-FI ug leitu ng werden 50cm Radargerate eingefuhr

MARCONI 5.0cm-RADARGERATE BEFINDEN SICH IN

bedeutet: Grossere Reichweite bei gegebener Senderleistung Durchdringung von Schlechtwettergebieten ohne Wirkungsverlust Kristal lgesteuerte FestzeichenunterdrUckung zur Ausschaltung von Storungen Sofo.rtige Betriebsbereitschaft nach langen Betriebspausen

WEITE, KLARE SICHT

MARCONI Vermessung, Planung, Installation un<;/ Pflege von vol/standigen Radaranlagen fur z ivile Zwecke, Landesverteidigung und Seefahrt

London Airport Johannesburg Gatwick Dunedin (Neuseeland) Ge nf Oberpfaffen hofen Boscombe Down Bitteswell Hong Kong Manchester Brussel Warton Kalkutta Hatfi e ld lstres St. Annes Birmingham Rom Jersey Bretigny Wellington (Neuseeland) Ostende Kopenhagen O hakea (Neusee land) und den Koniglic he n Forsch u ngsstel le n in : Farnborough Bedford und Pershore

RADAR DIVISIO N MARCONl' S WIRELESS TELEGRAPH COMPANY LIMITED CHELMSFORD, ESSEX. ENG LA ND

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