737 Flight Crew Operations Manual
Landing Gear -
System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
14.20.2 D6-27370-866-EGP
Landing Gear Transfer Unit
Hydraulic system B pressure is available for raising the landing gear through the
landing gear transfer unit. Hydraulic system B supplies the volume of hydraulic
fluid required to raise the landing gear at the normal rate when all of the following
conditions exist:
• airborne
• No. 1 engine RPM drops below a limit value
• LANDING GEAR lever is positioned UP
• either main landing gear is not up and locked.
Landing Gear Extension
When the LANDING GEAR lever is moved to DN, hydraulic system A pressure
is used to release the uplocks. The landing gear extends by hydraulic pressure,
gravity and air loads. Overcenter mechanical and hydraulic locks hold the gear at
full extension. The nose wheel doors remain open when the gear is down.
Landing Gear Manual Extension
If hydraulic system A pressure is lost, the manual extension system provides
another means of landing gear extension. Manual gear releases on the flight deck
are used to release uplocks that allow the gear to free–fall to the down and locked
position. The forces that pull the gear down are gravity and air loads.
With the manual extension access door open:
• manual landing gear extension is possible with the LANDING GEAR
lever in any position
• normal landing gear extension is possible if hydraulic system A pressure
is available
• landing gear retraction is disabled.
Following a manual extension, the landing gear may be retracted normally by
accomplishing the following steps:
• close the manual extension access door
• move the LANDING GEAR lever to DOWN with hydraulic system A
pressure available, and then
• position the LANDING GEAR lever to UP.
September 28, 2006
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