Background Information

• The European Aviation Safety Agency (EASA) Airworthiness Directives (AD) 2008 - 0158R1, which revised AD 2008 - 0158 concerning a design deficiency in Funkwerk TRT-800A and TRT-800H transponders, has been replaced by AD 2008 - 0183.
• Air Navigation Service Providers (ANSP) have reported, and flight trials have confirmed, the intermittent loss of detection on Mode S Secondary Surveillance Radars (SSR) of aircraft equipped with Funkwerk Avionics TRT-800A and TRT-800H. However, transponders marked as Mod-Index 10 (indicating that Funkwerk Avionics Service Bulletin (SB) TRT800-A-H-1 Revision 1.04 dated 17 October 2008, or a later approved revision of this document, has been incorporated), are not affected and reply correctly to Mode S interrogations.
• These unmodified transponders do, however, reply correctly to SSR Mode A/C only interrogations.

Impact on ATS Operations