Rockwell Collins issued a Service Information Letter, TDR-94()-18-1, on October 25, 2018, for the TDR-94/TDR-94(D) ATC/Mode S Transponder. The SIL addresses some anomalies experienced in the field by the Eurocontrol Center when running tests on the TDR-94.
Current software on TDR-94(D) models ending in -5xx may not respond correctly in all circumstances when receiving interrogations with the OVC functionality.
This has no flight deck effect and will only result in a reply being dropped by ground stations that have implemented the OVC functionality.
Rockwell Collins will be releasing new operational software to correct this issue. A SB (Service Bulletin) will be released to Service Centers to perform the software update. It is expected to be recommended and available no later than the end of December 2018.
All prior aircraft modifications/installations and TDR-94D modifications may need to have their transponders updated once the SB is released and if they fly in Europe they could experience a mode S reporting issue. Additional guidance on modifying fielded transponders will be provided when the FAA completes its impact analysis.
We are continuing to work closely with Rockwell Collins on this issue and will provide frequent updates as they become available. If you have any questions or suggestions don’t hesitate to contact your Duncan Aviation Avionics Installation Representative.