User's Manual

TT21/TT22 Transponder Installation Manual 13 July 2009
00560-00 Issue AF
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Page 30 Trig Avionics Limited
Equipment
Transmitted Integrity
Level
VFR only GPS or uncertified installation
Low
GPS installation certified for en-route and
terminal IFR navigation
Medium
GPS installation certified with augmentation,
such as WAAS or LAAS
High
6.1.10 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. When
configured for ADS-B, the TT21/TT22 will ask for the aircraft length and
width (wingspan), in metres, and will calculate the appropriate size code for
transmission.
6.1.11 ADS-B Test Message Option
Because of limitations in the ATC radar computer systems, in US airspace the
FAA require ADS-B equipped aircraft to periodically transmit their Mode A
squawk code in an ADS-B squitter message. This allows the computer system
to reconcile conventional radar traces with ADS-B information in a mixed
surveillance environment. Because the Mode A code does not form part of the
base ADS-B message set, the code is sent in a “TEST” message.
These special messages only need to be sent when the aircraft is visible to US
radar systems. The transponder already knows the geographic position of the
aircraft, and therefore the recommended option setting for these messages is
“Only in America”.