4.3.4 Reply Information - Speed Category (RI)
Besides AA, AC and FID another important part of the Mode-S data is
the Speed Category of the respective aircraft. This speed category shall
be configured in the setup and must contain one of the following codes.
4.4 Optional settings
4.4.1 Option Ground-Switch
If a ground switch is connected (and enabled in setup) the transponder is
able to determine on-ground and in-flight state. On-ground state is
activated automatically once the gear touches the ground. On-ground
state is indicated on display by symbol 'G' (apart from ‘F’ for In-flight-
state).
In On-ground-state, the transponder will reply differently to certain
addressed interrogations. Also, the transmission rate of some
periodically sent data (squitters, ADS-B) is reduced. This allows ATC to
distinguish between airborne aircraft and those on the ground and it
reduces the Mode S channel load.
For small aircraft, authorities normally do not require such a ground
switch. In this case, the transponder will use the same data formats on
the ground as in the airborne state.