LANDING GEAR AND
BRAKES
AIRPLANE
OPERATIONS
MANUAL
2-12-05
Page
2
Code
01
REVISION 38
AOM-145/1114
AIR/GROUND INDICATION SYSTEM
Air/ground indication is determined by a system that detects landing
gear shock absorber compression and relays information to the
landing gear electronic unit for gear control. The system consists of
five weight-on-wheel proximity switches. Two of them are installed on
each main landing gear leg and one on the nose landing gear leg.
The Landing Gear Electronic Unit (LGEU) processes the main landing
gear proximity switches’ signals information in four independent
channels and controls various equipment operations. Logic processing
includes the position signal and its validity. If all proximity switch
signals are valid, four signals are processed to assure that at least
three signals indicate identical status for releasing the air/ground
signal output.
Should one proximity switch signal be invalid, the logic will process the
remaining three signals so that at least two indicate the same status. If
a second proximity switch is invalid, the two remaining signals are
processed only if both send the same signal. Disagreement between
these two remaining proximity switches causes the Landing Gear
Electronic Unit to de-energize the channels and provide a default
output signal.
The nose landing gear proximity switch signal is sent only to the thrust
reverser logic (if installed) and steering control.
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