User's Manual

TT21/TT22 Transponder Installation Manual 13 July 2009
00560-00 Issue AF
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Trig Avionics Limited Page 29
6.1.5 Aircraft Category
To assist ATC tracking of aircraft, an aircraft category can be transmitted by
Mode S transponders. Using the rotary knob, select the aircraft category that
most closely matches the aircraft the transponder is installed in.
6.1.6 Squat Switch Source
The Squat switch input allows the transponder to automatically switch between
Airborne and Ground modes, and to automatically start and stop the flight
timer. The sense of the squat switch input can be selected using the rotary
knob. If the squat switch input is not connected the “Not Connected” option
must be selected.
6.1.7 GPS Input
If a GPS is connected for ADS-B position reporting, select the appropriate
interface protocol using the rotary knob.
6.1.8 GPS Line Speed
If a GPS has been selected at the previous step, you should select the
appropriate line speed using the rotary knob. Panel mount GPS units with
Aviation format outputs generally run at 9600 bps. NMEA GPS units
generally run at 4800 bps. Freeflight 1201 and NexNav 3101 GPS receivers
generally run at 19200 bps.
6.1.9 GPS System Integrity Level
An important metric for ADS-B ground system behaviour is the SIL or System
Integrity Level. It is intended to reflect the probability that the GPS position
source is providing erroneous information. A detailed analysis of the
contribution to system integrity is outside the scope of this manual, and the
installer may need to carry out a system safety analysis to determine the best
value to set. However, a reasonable guideline might be: