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NATS ADS-B Transponder Trial Tests GA Operators

By Juliet Van Wagenen | February 5, 2015
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[Avionics Today 02-05-2015] U.K. air navigation service provider NATS is leading a new trial that looks to bypass Automatic Dependent Surveillance-Broadcast (ADS-B) equipage for General Aviation (GA) operators when it comes to enabling their planes for effective aircraft tracking in the United Kingdom. The one-year trial, which began in late December, banks about 45 participants thus far who are encouraged to connect their non-certified GPS receivers with Mode S transponders in order to enable ADS-B functionality, upping safety while, potentially, easing cost and hassle.

Digram of ADS-B enabled GA airspace
Diagram of ADS-B enabled GA airspace. Photo: NATS

Currently, the Air Navigation Service Provider (ANSP) is finding it difficult to track GA aircraft in the busy and complex airspace of Southeast England. NATS is hoping that the trial will provide an affordable solution that can encourage GA operators to equip and, in turn, improve overall airspace security.

“We have quite a large airspace infringement issue across the NATS operation and particularly in the Southeast of England,” Jonathan Smith, NATS general aviation lead told Avionics Magazine, noting that thus far the ANSP has implemented a range of measures to mitigate the airspace intrusion by GA pilots who might wander into controlled airspace. “But one clear facet of these events is that we are far better able to mitigate the risk if we have electronic emission off the airframe. Now, I’m not necessarily saying a transponder, for obvious reasons, but what I [as an air traffic controller] need to be able to do is to detect the presence of the airplane electronically at which point I can enable all kinds of electronic safety nets, which I know can deliver genuine protection from the risk of the incursion taking place.”

According to Smith, the riskiest events that occur as far as airspace intrusions often come from aircraft for which Air Traffic Controllers (ATCs) cannot detect vertical extent. This means that ATCs often has to assume that a GA aircraft is operating below controlled airspace based on a radar return without information on how high the plane is flying, but if this isn’t the case, then safety takes a huge hit. If the transponder is able to provide a more pinpointed location, an ATC can enable safety nets to keep GA operators separated from commercial airliners or other aircraft that may be operating nearby.

The trial is part of a larger project known as the Electronic Visibility via ADS-B (EVA) program, operated in partnership with AOPA UK, Trig Avionics, Funke Avionics Gmbh and Eurocontrol, with additional funding from the Single European Sky ATM Research Joint Undertaking (SESAR JU). Another part of the trial aims to introduce a new prototype device called the Low Power ADS-B Transceiver (LPAT), developed by NATS and Funke Avionics, which is a portable, battery-powered and more affordable device that will provide the minimum functionality necessary to make GA pilots visible to others in airspace.

Additionally, the trial looks to demonstrate to both pilots and regulatory authorities alike a way in which operators can equip with ADS-B without incurring enormous costs along the way.

“A lot of GA pilots quite resent, and it has been pointed out to them, that at the moment they have a piece of equipment [already on their aircraft] that is capable of transmitting an ADS-B position. But they don’t take advantage of that facility because, up to this point, legislation has said that you can only transmit an ADS-B position if it is derived from a certified GPS source. That is the key to it as many, many airplanes are flying around with a lightweight transponder at the moment but the transponder is not connected to a GPS, which is probably already installed in the airplane,” said Smith.
The problem for many operators is that a certified GPS often costs around $5,500 — far above a GA pilot’s budget. However, many non-certified GPS are already on board most aircraft and hooking up the transponder can be as simple as soldering a few wires, Smith says.

Regulatory authorities such as the U.K.’s Civil Aviation Authority (CAA) and the European Aviation Safety Agency (EASA) believed many ANSPs wouldn’t allow a non-certified signal for tracking purposes, however, thus limiting tracking options.

“We got many answers back [from regulatory agencies], mainly around that the air traffic service provider would not put up with an uncertified emission being derived from an uncertified GPS, and we sort of answered that by going, ‘well, we’re the air traffic service provider and we think we can cope with it,’” said Smith. NATS believes that the transponder can be flagged to indicate that it is uncertified and, therefore unreliable. “We would not envisage controlling an aircraft on the basis of an uncertified ADS-B emission alone but we would take advantage of that data to provide us an alert to the presence of that aircraft.”

The year-long trial is still within the first month and, as spring approaches and GA pilots in Southeast England begin dusting off and rolling out their aircraft, Smith is hoping that around 100 will take the time and action to participate. The CAA is also helping to encourage the trial by waiving the minor modification fee for qualifying annex II aircraft for those wishing to connect their transponders to a non-certified GPS receiver and begin broadcasting their position via ADS-B — although pilots will be expected to provide their own transponders and GPS devices.

Should the trial be successful, Smith hints that it’s possible to use the tech and concept further on non-traditional aircraft to more effectively integrate everything that flies in U.K. airspace.

“We’ve got some complex airspace in the Southeast of England and we’re always looking for very clever, out-of-the-box ways to use that airspace and share that airspace more effectively,” said Smith. “The concept of being able to fit this ADS-B transceiver on, perhaps, non-traditional GA platforms like parameters and even small [Unmanned Aircraft Systems] UAS — drones — to perhaps more effectively share busy, complex airspace is something I think is quite exciting.”

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