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AVIONICS
AVBUYER.com Fig A: SIMPLIFIED DEPICTON OF LAND AND OCEANIC ATC COVERAGE
This is less than optimal, because using ADS-C and traditional voice communications mean less frequent updates of the aircraft’s position and, as a result, greater required separation between aircraft both laterally and vertically.
It’s More Than ADS-B Surveillance
It takes more than just surveillance to operate anywhere. Aircraft are equipped to communicate, navigate and have surveillance capability. These three elements of conducting flight fall under the heading ‘CNS’. While surveillance and communication are also the domain of ATC, navigation is specific to the aircraft. So improved CNS is the key to closely separated oceanic and remote flight tracks. The communications piece is via CPDLC, using reliable and consistent data, rather than voice. Under the CPDLC umbrella sit: • •
VDL (using line of sight datalink to communicate intentions between aircraft and en-route air traffic), and FANS (using HFDL and SDL to communicate similar intentions over oceans and remote areas where VDL coverage is inadequate).
The navigation piece relies on highly accurate positioning and flight plan tracking, derived from Global Positioning Satellites (GPS). The WAAS version of GPS is a crucial component of the surveillance also, being the required position
output of ADS-B Out (Version 2). Aircraft are required to have different degrees of navigational capability, based on where they intend to fly. These variations are covered under RNP and Area Navigation (RNAV), where there are varying degrees of allowable flight track deviation. Note that apart from CNS, an aircraft’s physical ability to maintain the flight path and its navigation system commands is also important. Maintaining altitude (RVSM) using fine-tuned air data systems is one method to achieve it. Another is the aerodynamic performance of the aircraft. Yet another is the ability of the flight control system to maintain heading, roll and track angle.
Introducing Space-Based ADS-B
Figure A (above) introduces SB ADS-B, serving the same functionality and purpose over remote regions and oceans as ground-based ADS-B Out currently provides over terrestrial surfaces. Figure B (below), meanwhile, brings together the CNS elements as they apply to four different types of worldwide airspace. The more advanced and ‘on-track’ the CNS is, the safer it is for everyone wanting to fly favorable tracks. (Tracks are favored because of variable winds, fuel burn rates, actual distance flown and several other factors.) With everyone wanting to squeeze into these tracks, it is understandably difficult to safely maintain minimum separation. Obviously, if everyone had FANS and RNP4 capability, it would also be easier to maintain
Fig B: AIRSPACE, METHODS AND SEPERATION REMOTE AIRSPACE
COMMS - SATCOM OR HF NAVIGATION – RNP 10 SURVEILLANCE - PROCEDURES
SEPARATION WITHOUT ADSB LONGITUDE: 10 MIN OR 80 NM LATITUDE: 60 NM
SEPARATION WHEN ADSB LONGITUDE: < 10 MIN OR 80 NM LATITUDE: < 60 NM
VHF AIRSPACE (NO ADSB)
COMMS – VHF VOICE & VDL NAVIGATION – RNP 10 SURVEILLANCE - PROCEDURES
SEPARATION WITHOUT ADSB 10 MIN OR 80 NM
SEPARATION WHEN ADSB 5 NM NAVIGATION RNAV 2-5
ADS-C AIRSPACE
COMMS – CPDLC & HF NAVIGATION – RNP 4 SURVEILLANCE – ADS-C
SEPARATION WITHOUT ADSB 30 NM
SEPARATION WITH ADSB < 15NM
VHF AIRSPACE (WITH ADSB)
COMMS – VHF VOICE & VDL NAVIGATION – RNAV 2-5 SURVEILLANCE – ADS-B OUT RADAR & WAM
SEPARATION WITHOUT ADSB 5 NM
SEPARATION WITH ADSB 5 NM
116 Vol 23 Issue 5 2019 AVBUYER MAGAZINE A
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