Engineering Matters

Including:

LAA-issued instructions for continued airworthiness, fixing faults before flying, and one thing to bear in mind – woodworm does not just inhabit furniture…

Welcome to Engineering Matters – the section of Light Aviation that is dedicated to discussing all manner of topics concerning both technical and operational aspects of the LAA fleet. If you have anything to say that you think would benefit others, then please email words and pictures to LAA Engineering at engineering@laa.uk.com

Cessna 120/140 seat harness attachment brackets

In 2015, the FAA issued Special Airworthiness Information Bulletin CE-15-13 for Cessna 120 and 140 following the investigation into a fatal accident. The aircraft overturned after a departure from the runway on take-off, and the centre bracket securing the seat harness lap straps, failed.

The investigation found that the centre bracket (part number 0425132) on some aircraft was made of aluminium and it was this bracket that failed in the accident. Replacement brackets supplied by Cessna are made of steel.

The recommendation in the FAA SAIB was to carry out an inspection of the bracket with a magnet to check if the installed brackets were of aluminium or steel. It is likely that the FAA may issue an Airworthiness Directive in the near future following another fatal accident in 2015. The FAA AD would mandate the replacement of the aluminium brackets. Cessna also issued Service Bulletin SEB-25-03 in February 2015 on this subject.

This subject was highlighted previously in the April 2015 issue of the Light Aviation Safety Spot, which is linked in the Cessna 120 TADS 823 (available from the LAA website Data Library). If the FAA AD to issue the proposed Airworthiness Directive, this will also be referenced in TADS 823.

Corroded gyro bolts

Experienced gyro inspector, Graham Shackleton, has come across a number of gyros recently which have severely corroded attachment bolts. The affected bolts were undercarriage and rotor blade attachment bolts. These bolts come under different stresses and loads but regardless of their purpose, hardware should be replaced once they start to corrode. Replacing corroded bolts is a bit like frequent engine oil changes – cheap maintenance that prevents something unsafe and far more expensive occurring.

Although there is a specific range of serial numbers listed in the Service Bulletin (and in the proposed FAA AD), LAA Engineering recommends all Cessna 120 owners check the bracket and replace it if it is of the aluminium type.

LAA-issued Instructions for Continued Airworthiness

The titles of LAA-issued Instructions for Continued Airworthiness (ICA) have recently been amended to simplify the various types and the way that they are classified. Previously issued Alerts and Airworthiness Information Leaflets remain current, unless superseded.

The types of ICA now issued by LAA Engineering are:

• Alert:

An Alert is produced by LAA Engineering for information purposes only. Although compliance with an Alert is not considered mandatory, the Alert may contain news of ICA from other sources that is mandatory in its own right, such as a CAA Mandatory Permit Directive. LAA Alerts are equivalent to the previously issued LAA Airworthiness Information Leaflet Classification C.

• Technical Service Bulletin:

Compliance with an LAA Technical Service Bulletin (TSB) is recommended for the applicable LAA-administered aircraft. LAA Technical Service Bulletins are equivalent to the previously issued LAA Airworthiness Information Leaflet Classification B.

• Mandatory Technical Directive: An LAA Mandatory Technical Directive (MTD) is considered mandatory for the applicable LAA-administered aircraft. LAA Mandatory Technical Directives are equivalent to the previously issued LAA Airworthiness Information Leaflet Classification A.

Fournier RF5 repairs

LAA Inspector, Dave Bland, is carrying out an in-depth refurbishment of a Fournier RF5 motor glider and has come across some examples of why you cannot assume everything is going to be fine forever.

Apart from some slightly dubious previous repairs, the tailplane attachment brackets have suffered from severe exfoliation corrosion. Dave says that there is an Airworthiness Directive for inspecting the brackets but many people assume it refers to the more visible steel brackets mounted on the fuselage than the associated aluminium

Pattern parts – Rotax carbs and hoses

LAA Engineering has recently been informed of the discovery of some ‘below standard’ pattern parts used on some Rotax 912 engines. These included carburettor mounting sockets and carburettor diaphragms. Quite often, parts are advertised as being to an equivalent standard to the Original Equipment Manufacturer (OEM) specification and visually they might look identical. Buyer beware – the parts may not be made to the same specification by material or dimension and therefore do not function correctly or for as long.

In some cases, such as factory-built gyros, non-OEM parts may not be installed without specific approval by the manufacturer or by applying for a modification.

It recently came to light that a number of factory-built gyros had non-OEM silicone coolant hoses fitted. In this case it is entirely possible that the specification of the silicone hose exceeded that of the OEM part but it still cannot be used in this instance without manufacturer’s approval or as an approved modification.

Ground running and fault rectification before flight

Fairly regularly, LAA Engineering receives emails or telephone calls from owners requesting assistance with fault diagnosing a problem with their aircraft. More often than you would like to hear, is a comment that an aircraft was flown after an attempt to find the cause of engine issues where nothing was found or even to try and ‘clear the problem in the air’.

It is very rare that an engine fault cannot be reproduced on the ground or that a definite cause cannot be found. Rectifying intermittent faults can be very time consuming and frustrating, but with all fault diagnosing, persevere and if necessary, consult with others before getting airborne again. Aeroplanes are clever but rarely do they cure themselves!

brackets mounted in the tailplane. Obviously, it isn’t only the brackets (steel and aluminium) that can corrode but also the bolts that attach them.

Another area of concern in the wood structure was what appears to be signs of a woodworm ‘infestation’. Fortunately, Dave managed to ascertain that the woodworms appear not to like the taste of the Aerodux glue or the taste of plywood, so the damage was restricted to only certain areas.

Kitfox fuel tanks

LAA Engineering has received information from two Kitfox owners with fuel tank problems.

The fuel tanks are made of fibreglass and have both suffered internal failures where the internal ribs are bonded to the bottom skins of the fuel tanks.

At this time, it is not known why the tanks have failed in this way. It may be due to poor initial build quality where there was insufficient bonding at the rib to skin junction or alternatively, it may be the long-term effects of the fuel.

Owners should be on the lookout for any bulging of the lower surface of the fuel tank where the internal ribs are no longer attached to the bottom of the tank.

Leburg ignition failure

The Hall Effect timing sensor magnets are epoxied into the spinner backplate. Later variants are an interference fit into the spinner backplate or bespoke mounting plate.

The Leburg electronic ignition system has been a popular upgrade for VW engines in the LAA fleet for many years. In 2021, a Turbulent suffered an engine failure after take-off and was very badly damaged in the ensuing forced landing. While severely injured, the pilot survived and the use of a five-point harness and RAF-spec helmet no doubt limited his injuries.

Inspector Paul Jenkins led a very detailed investigation into possible causes for the engine stoppage with further information provided by the Leburg supplier, Skycraft Ltd.

As mentioned in a previous Engineering Matters (January 2022), it was initially thought that the ignition may have failed when the switch terminals became loose. Further investigation found one of the ignition system’s two Hall Effect timing sensor magnets was no longer mounted on the spinner backplate.

It could not be determined whether the magnet had departed in flight but if it had, depending on how the ignition system had been wired, the loss of one of the magnets could result in both ignition systems shutting down.

Neil Spooner, another Leburg-savvy inspector, reported that when one of his Leburg controllers failed, he found that the nuts holding down the circuit boards had come loose, shorting out the integrated circuit. Neil recommends checking that the nuts are correctly torqued. It may be only earlier units like his that are affected.

LAA Engineering intends to produce more information on this in due course but meantime, if in any doubt, please refer to the installation information or contact Skycraft Ltd for further advice.

Europa door latch stop alert update

LAA Engineering issued the Europa Door Latch System Stop Alert and AIL on 1 November 2021 and by now, all flying Europas should have complied with the requirements. Without prior consultation with the LAA, the CAA issued MPD 2022-003 on 03 February 2022 and a corrected version on 16 February mandating compliance with the AIL and Standard Modification.

Compliance with the MPD is legally mandatory, although at this time, the LAA is uncertain as to whether the MPD is a proposed or actual MPD (the wording on the MPD is ‘mixed’). LAA Engineering is currently awaiting comment from the CAA regarding the MPD status and numerous other errors within. If any doubt, where the LAA AIL has been complied with, it may be deemed prudent to also confirm compliance with MPD 2022-003.

Piper rudder failures

The NTSB in America have issued Aviation Investigation Report HTSB/AIR-22-02 highlighting recent rudder failures on two Pipers, one a PA-12, the other a PA-14. The failures occurred in flight and the rudder post fractured above the upper hinge allowing the top of the rudder to fold over onto the upper tail bracing wires. Not surprisingly, this resulted in a restriction to the rudder range of movement and the associated reduction in control of the aircraft.

The failures appear to have been confined to rudders with the Piper part number 40622 and that the rudder posts were made of AISI 1025 carbon steel and likely fractured to fatigue.

The failed rudders had no part numbers on them but both were identified by the material spec and dimensions of the p/n 40622 rudder. This rudder was fitted to a number of Piper models.

In all, five aircraft were examined by the NTSB and in addition to the two failed rudders, three other aircraft showed evidence of fatigue cracks appearing. The other three aircraft were wheel equipped-aircraft. What was of note was that all five inspected rudders had aftermarket beacons or strobe lights installed on the top of the rudder. The added surface area and mass of the lights would likely increase the stresses.

Gascolator

Luscombe owner, Ron Parker, has reported his findings when investigating a fuel weep from the inlet side of the Tillotson fuel gascolator. Once the gascolator top had been removed, close inspection showed that there was a defect in the inlet area of the casting. The defect may have been caused by there being insufficient metal in that area, corrosion weakening that point or perhaps the effects of a tapered union being installed into the top too tightly.

Cast gascolator tops that use the bail-wire to retain the bowl suffer over time with the constant pulling down on the gascolator top. This causes a warp in the lid resulting in the bowl not sitting flat against the top. Despite the fairly thick rubber gasket between the top and the bowl, any slight pressure on the gascolator will cause a fuel leak. Piper PA28 gascolators suffer from this and later versions were milled from solid aluminium. There is always the chance that some amateur-built aircraft have gascolators that started life installed in a PA28. Similarly, Tillotson gascolators may be used on more than just Luscombes.

Left Many types of cast gascolator tops may suffer over the years. Cause of the fuel weep was not obvious until looking at the underside of the top.

PTFE tape

Following on from my comment previously in Engineering Matters that PTFE tape should not be used on aircraft fuel systems, Pat Thody emailed to say that in his opinion, having worked with PTFE all his working life, PTFE is unlikely to be affected by any chemicals or solvents used in aircraft.

In theory, in aircraft systems, sealant should not be required at all, if the O-rings, crush washers, flared pipes, gaskets and tapered fittings do their jobs as designed.

There is always the possibility that tape or sealant may, if not used correctly, cause an obstruction in the system. As mentioned, there are products out there that prevent galling of threads when assembling (as well as acting as a sealant) and the use of PTFE tape as a sealant in aircraft fuel and oil systems is not considered ‘normal aviation practice’.

LAA Engineering charges

LAA Project Registration

Kit Built Aircraft £300

Plans Built Aircraft £50

Initial Permit issue

Up to 450kg £450

451-999kg £550

1,000kg and above £650

Permit Revalidation

(can now be paid online via LAA Shop)

Up to 450kg £170

451-999kg £220

1,000kg and above £260

Factory-built gyroplanes* (all weights) £275

*Gyros note: if the last Renewal wasn’t administered by the LAA, an extra fee of £125 applies

Modification application

Prototype modification minimum £60

Repeat modification minimum £30

Transfer

LAA Engineering housekeeping

Email attachments: Please ensure that any picture and document emailed to LAA Engineering are sent as attachments rather than in the body of the email. When embodied into the email, pictures often resize themselves to either low resolution, unreadable pictures or become massively enlarged. Scans of documentation must be of a high quality. Weight & balance reports: When an aircraft is reweighed, a copy of the new weight and balance report should be sent to LAA Engineering to be kept with the aircraft’s records. Obviously, the original report should be kept with the aircraft’s documents but it would appear that they have often gone missing by the time an aircraft is sold on. LAA Engineering will normally be able to provide a copy of the previous report on request but only if one is on file. If the aircraft has not been weighed within ten years, it is recommended that it is reweighed in any case. ■

LAA Fleet Summary

Aircraft with current Permits to Fly: 2,857

Aircraft with ‘project’ status: 1,565

(from C of A to Permit or CAA Permit to LAA Permit)

Up to 450kg £150

451 to 999kg £250

1,000kg and above £350

Four-seat aircraft

Manufacturer’s/agent’s type acceptance fee £2,000

Project registration royalty £50

Category change

Group A to microlight £150

Microlight to Group A £150

Change of G-Registration fee

Issue of Permit documents following G-Reg change £55

Replacement Documents

Lost, stolen etc (fee is per document)£20

PLEASE NOTE: When you’re submitting documents using an A4-sized envelope, a First Class stamp is insufficient postage.

Number of aircraft types approved: 520

Recent Alerts & AILs (check the LAA website for further details)

Zivko Aeronautics Inc. Edge 360, Edge 540 and Laser Z200: Aileron Centre Hinge Attachment

CAA MPD: 2022-001

LAA Alert: A-001-2022

MT-03, MTOsport, MTOsport 2017, Calidus and Cavalon: Rotor Blade Inspection/Replacement/

Life-Limitation

CAA MPD: 2002-002

LAA Alert: A-002-2022

TLAC Escapade and Sherwood Scout: Seat locking and Secondary Seat Restraint

CAA MPD: 2022-004-E

LAA TSB: TSB-001-2022

Europa: Door Latch System Stop

CAA MPD: 2022-003

LAA AIL: MOD/247/012

LAA Alert: LAA/AWA/21/08

Adjustable Seats in General Aviation Aircraft

CAA Safety Notice SN-2022/001: Security and locking of adjustable seats