FAA has issued a Safety Alert For Operators (SAFO 10003, .PDF
) urging operators of a wiring flaw on Bombardier CRJs with Rockwell/Collins model TDR-94D transponders. The problem can prevent the unit from working correctly when the planes are at airports equipped with certain surface safety systems, including Airport Surface Detection Equipment, Model X (ASDE-X), Advanced Surface Movement Guidance and Control System (A-SMGCS) and Precision Runway Monitoring (PRM). From the SAFO:
At these airports, the 1090 MHz systems may experience interference caused by certain Bombardier Regional Jets. Investigation of this problem revealed that TDR-94D transponders, part numbers 622-9210-004/-005/-006/-007/-207/-008/-108/-308/-408 do not inhibit replies to “ALL CALL” interrogations due to an improper wiring of the Air/Ground #1 and Air/Ground #2 inputs on the transponder. Improperly wired aircraft prevent transponders from correctly suppressing replies to Mode A/C/S all-call and Mode S-only all-call interrogations while on the ground. These transmissions cause interference and are an airspace safety concern since it reduces the ability of Traffic alert and Collision Avoidance System (TCAS) in the terminal area to acquire and track aircraft and reduces performance of the air traffic control (ATC) ground systems including Secondary Surveillance Radars (SSR), ASDE-X, PRM, A-SMGCS and 1090ES Automatic Dependant Surveillance –Broadcast (ADS-B).
[R]elocate one wire Air/Ground pin in the transponder rack from the #1 position to the #2 position in order to prevent the condition described above.
How-to details are available in Rockwell/Collins Service Information Letter, TDR-94( ), SIL 07-1 or Bombardier Service Bulletins 601R-34-146 and 670BA-34-029.