User's Manual

TT21/TT22 Transponder Installation Manual 13 July 2009
00560-00 Issue AF
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Page 50 Trig Avionics Limited
Experimental ADS-B
Surveillance
ADS-B trials have taken place in a number of
countries which, because of the experimental
nature, have allowed deviations from the
operational standards represented by AMC20-
24, but which have been based on positional
information with comparable integrity.
ADS-B Information
There are a number of non-certified applications
of ADS-B technology such as fleet monitoring
and traffic awareness which can be deployed
using position sources of lower integrity which,
because the integrity is reported in the
transmissions, are also compatible with the
ADS-B surveillance environment.
There is also a widely publicised fourth level of service in discussion which is
the US “Next Generation” plan, but at the time of publication of this manual a
number of key aspects of this are undefined and no compliance statement
against that future plan is practical.
The TT21/TT22 is designed to provide all of the required parameters listed in
AMC20-24. However, in order to be used for separation services AMC20-24
sets additional criteria related to the position accuracy and integrity of the GPS
position source used, and the ability for the GPS to communicate those
accuracy and integrity parameters to the ADS-B output system in the
transponder. At the publication date of this manual, the only commercially
available GPS receivers we are aware of that can be used with the TT21/TT22
to meet the system requirements of AMC20-24 are the Freeflight 1201 and the
NexNav 3101.
A wide range of other GPS receivers can be used as the position source for
ADS-B, including ETSO-129a receivers and simpler VFR GPS receivers.
Whilst these receivers may be suitable for Informational or Experimental
installations, they generally lack one or more of the required integrity
parameters for an operational IFR separation application.