
Generic TT31 Minor Modification
21 February 2008
SUP/TT31/001
Issue
1.6
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Trig Avionics Limited
Page 3
2. Introduction
The TT31 Mode S panel mount transponder is an ED-73B Class 1 compliant Mode S level 2 datalink
transponder, with support for extended squitter, which also meets the relevant environmental
requirements of ED-14D. The TT31 meets the European requirements for Mode S Elementary
Surveillance and is certified to ETSO 2C112b.
The TT31 is targeted at the light aircraft retrofit market, and is designed to be compatible with the
existing wiring and installation provisions of current Mode A/C transponders. In addition to this
general compatibility, the TT31 is physically directly compatible with the Bendix/King KT76A and
KT78A Mode A/C transponder. Replacement of a KT76A or KT78A may therefore be able to reuse
some or all of the existing mounting provisions. Replacement of other transponders is expected to re-
use the existing antenna, altitude encoder, and circuit breaker, and may also use some or all of the
existing wiring harness.
This minor modification describes the process of upgrading an existing Mode A/C transponder to a
TT31.