Regulators urged to act quickly as fault on Honeywell device causes flight details to disappear from radar screens

With aircraft suddenly disappearing from radar screens, air traffic controllers are calling on European safety regulators to speed up approval of a solution for a recurring fault afflicting Honeywell’s Primus II transponder.

European controllers lose identification and flight details for an aircraft around five times a month, says the International Federation of Air Traffic Controllers (IFATCA). The data loss also disables air traffic control safety-net systems – short-term conflict alert and the airborne collision avoidance system (ACAS) of the aircraft concerned.

IFATCA has written to the European Aviation Safety Agency (EASA), Eurocontrol and the Joint Aviation Authorities to try to accelerate the process of approving a permanent modification to the transponder to supersede the current operational “fix” proposed by Honeywell. IFATCA says EASA is shortly to publish an airworthiness directive (AD), but under present rules it would give carriers a year to comply, which it says is too long. Meanwhile, Honeywell says it has had a software fix available “for a while”, and airlines can obtain it by returning the transponder. It also has a rotable pool of units for loan.

The Honeywell Primus II Mode S (elementary) transponder has been fitted in some aircraft since September 2004. The problem has usually involved Embraer ERJ-135/145 regional jets and occurs when pilots are asked to change their four-digit “squawk” code – the flight identification code allocated by the ATC unit; if they take more than 5s to input the new code the transponder automatically switches to “standby”, making it unresponsive to interrogation by ground radar or by the ACAS transponders of other aircraft. In areas where there is only secondary radar with no primary radar back-up, the contact disappears from the controller’s display. IFATCA cites a case this year over France where an ERJ-145 flew for more than 30min in busy airspace without radar contact.

Honeywell has told pilots to select the transponder to standby before inputting the new code, then back to active once the code has been set; or they can check the annunciators on the unit or on the ACAS display after a reset, and if they indicate standby they should select the transponder to active.

The latter advice was accepted in January as “a mitigation procedure” by Eurocontrol’s Mode S regulatory group. “In themselves [these measures] are not a permanent solution,” says Eurocontrol, adding that EASA’s proposed AD is “expected to be released shortly”.


Source: Flight International