OPERATIONS MANUAL

Navigation Systems
Radio Altimeter System:
The aircraft is fitted with a low-range radio altimeter system which measures
the obstacle clearance altitude, also called radio altitude (RA). The system is
designed for low altitude operation up to 2500 ft RA. The altitude data is sent
to the EFIS, to various alerting systems, and to the flight control computers.
The radio altimeter system comprises three independent units; each unit
includes a transmit antenna and a receive antenna. The system is calibrated
so that during landing the following RA values are indicated:
• When the aircraft pitch attitude is circa 3°, and the lower wheels on the
tilted main gear trucks touch the ground, the RA indication reads 0 ft. At
this point, the aircraft systems are still in air mode.
• When the gear trucks are no longer tilted, that is, when all main wheels are
on the ground, the RA indication is in the range of -2 to -4 ft. At this point,
the aircraft systems change to ground mode.
• When the nose gear is on the ground and all gear struts are compressed,
the RA indication is in the range of -6 to -8 ft, depending on the aircraft
weight and balance.
Antenna locations
Three RA
receive
antennas
Three RA
transmit
antennas
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