TT26 ADS-B Transponder Installation Manual
24 January 2017
01633-00
Issue AC
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20
Trig Avionics Limited
6.1.5
Squat Switch Source
The Squat switch input allows the TT26 to automatically switch between
Airborne and Ground modes. If the squat switch input is not connected the
“Ignore Squat Switch” option must be selected.
6.1.6
Aircraft Length and Width
On the ground, ADS-B transmits encoded aircraft size information which is
used by ATC to identify taxiing routes and potential conflicts. The aircraft
length and width (wingspan) should be configured.
6.1.7
GPS Antenna Offset
The GPS antenna offset is used together with the aircraft length and width to
manage taxiway conflicts. A typical GPS installation does not report the
geographic position of the centre of the aircraft, or even the tip of the nose of
the aircraft; instead it usually reports the location of the actual GPS antenna
(not the GPS receiver). In normal flight operations this distinction is of no
practical importance at all, but if ADS-B is used to manage taxiway conflicts, a
significant offset in antenna position could mean that the aircraft is not in the
same place as the ADS-B reported position. Although primarily intended for
position correction on large transport aircraft, General Aviation aircraft can
also have a significant offset. For example, if the aircraft has a long tail boom
and the GPS antenna is on the top of the tail, the GPS position could be 4
metres or more from the nose of the aircraft.
Enter the position of the GPS antenna relative to the nose of the aircraft. The
position is stored and transmitted to the nearest 2 metres; great accuracy in
measurement is not required.
6.2 Interface Configuration
6.2.1
Altimetry Source
The transponder has an internal altimeter, and that is the primary source for
altimetry. The system can also be configured to use an external air data
