Trials Show the Safety Benefit of Mode C Data

Date: 04 July 2007

Data released today by the UK Civil Aviation Authority (CAA) and NATS, the UK’s leading air navigation service provider, shows that many pilots flying outside controlled airspace could enhance their safety by making better use of current transponder equipment fitted to their aircraft.

A new procedure being undertaken by NATS allocates transponder codes to aircraft receiving an air traffic service from ‘London Information’. Although the Flight Information Service Officers providing the service have no radar, the unique code allocated can be seen by other radar controllers and tells them that the aircraft in question is currently on the London Information frequency. This enables controllers to pass any relevant safety information to the aircraft, such as warnings of impending airspace infringements or navigational advice and assistance if an infringement has occurred.

Since the procedure commenced in November 2006, eleven potential airspace infringements have been prevented by the new system and seven actual airspace infringements have been more speedily resolved. Steve McKie, NATS Division of Safety, said: “In each of these cases a potentially serious incident has been averted by a radar controller spotting the risk and contacting the Flight Information Service Officer. They have then passed the information on to the pilot, enabling appropriate action to be taken to avoid the infringement or to clear controlled airspace in the safest manner.

“Without this procedure it is highly probable that each of these eleven cases would have resulted in an airspace infringement and the potential consequences that come from it, and the seven infringement incidents would have resulted in greater risk and disruption than actually occurred.”

A trial is also taking place at Luton and Stansted where, in designated areas, aircraft can select a squawk to indicate to the radar controllers that they are listening out on the frequency. This trial, detailed in Aeronautical Information Circular 4/07 (Yellow 228), reduces radio transmissions from aircraft that may have previously requested a listening watch or a Flight Information Service, but still enables the controller to call and quickly identify an aircraft that looks likely to infringe controlled airspace. A similar trial is being carried out in the Manchester Low Level Corridor and early results are currently being evaluated.

A separate survey by the NATS air traffic control unit at Glasgow showed that over 40 per cent of aircraft receiving a service from the unit were displaying no Mode C transponder information.

In the trial, which ran during March and April 2007, 381 squawks were given to aircraft. Of these 270 automatically displayed Mode C information. Another 47 showed the data when asked by air traffic control and 64 advised that they were unable to show Mode C data.

Phil Roberts, Chair of the CAA’s Airspace Infringements Working Group, said: “The London Information procedure clearly shows the safety benefit in selecting Mode C on a transponder if it is available. Unfortunately the data from Glasgow shows that many pilots are simply not doing so.

“There is no justifiable reason for not selecting Mode C when it is available. A commercial aircraft’s collision avoidance system will provide a significantly enhanced separation if it receives Mode C data and the extra information available on a controller’s radar screen may allow them to prevent a serious incident. Fears that the CAA will use Mode C data to prosecute any infringing pilot are simply misplaced and the statistical data shows this clearly.”

For more information please contact Jonathan Nicholson (CAA) 020 7453 6027 or Richard Wright (NATS) 01489 615945.