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mode), an air/ground signal is provided to relays which control various system
functions.
Nose gear extension sensing provides a signal to relays controlling functions in the
stall warning and nose gear steering systems.
Landing Gear Operation
The landing gear are normally controlled by the Landing Gear lever. On the
ground, the lever is held in DN position by an automatic lever lock. The lever lock
can be manually overridden by pushing and holding the Landing Gear Lever Lock
Override switch. In flight, the lever lock is released when the main gear are tilted
and the body gear is centered.
If any main gear is not tilted in flight, the disabled system message TILT displays
on the gear synoptic adjacent to the affected gear.
December 01, 1999
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
14.20.2 D6-30151-425
Landing Gear -
System Description
Each main gear has one hydraulically actuated and one mechanically acutated
gear door. The nose gear has two hydraulically actuated and two mechanically
actuated gear doors.
Landing Gear Retraction
When the Landing Gear lever is moved to UP, the landing gear begin to retract and
automatic braking occurs. The landing gear doors open and the main gear tilt to
the retract position. The EICAS landing gear position indication display changes
from a green DOWN indication to a white crosshatch in–transit indication as the
landing gear retract into the wheel wells.
After retraction, the main gear are held in the up position by uplocks. The nose
gear is mechnically locked in the up position. The EICAS landing gear position
indication changes to UP for 10 seconds and then blanks. Positioning the Landing
Gear lever to OFF depressurizes the landing gear system.
If any gear is not up and locked up after the normal transit time, the EICAS gear
position indication changes to the expanded non–normal format, with the affected
gear displayed as in–transit, or down if the gear never unlocked from the down
position.
The disabled system message TILT displays on the gear synoptic adjacent to the
affected gear.
Landing Gear Extension
When the Landing Gear lever is moved to DN, the landing gear doors open, the
gear are unlocked, and the in–transit indication is displayed on the EICAS landing
gear position indication.
The gear free–fall without hydraulic power to the down and locked position. The
downlocks are powered to the locked position, all hydraulically actuated gear
doors close, and the main gear trucks hydraulically tilt to the flight position. When
all gear are down and locked, the EICAS gear position indication displays DOWN.
If any gear position disagrees with lever position after the normal transit time the
EICAS gear position indication changes to the expanded non–normal format, with
the affected gear displayed as in transit (or UP if the gear never unlocked from the
up position).
Landing Gear Alternate Extension
Alternate gear extension is activated by pushing the Alternate Gear Extend
switches. The gear uplocks and gear door latches are released, allowing the gear
to free fall. Gravity and airloads extend the gear and springs pull the downlocks
into the locked position. All gear doors remain open after alternate extension.
The EICAS landing gear position indication displays the expanded gear position
indication when the alternate extension system is used.
April 1, 2000
747 Operations Manual
Landing Gear -
System Description
Copyright © The Boeing Company. See title page for details.
D6-30151-425 14.20.3
Nose Wheel and Body Gear Steering
Nose wheel and body gear steering is powered by hydraulic system 1.
Primary low speed steering control is provided by a nose wheel steering tiller for
each pilot. Limited steering control is available through the rudder pedals. The
tillers can turn the nose wheels up to 70 degrees in either direction. A pointer on
the tiller assembly shows tiller position relative to the neutral setting. The rudder
pedals can be used to turn the nose wheels up to 7 degrees in either direction. Tiller
inputs override rudder pedal inputs.
Body gear steering operates when the nose wheel steering angle exceeds 20
degrees. This reduces tire scrubbing and lets the airplane turn in a minimum
radius. Body gear steering is activated when ground speed decreases through 15
knots. As speed increases through 20 knots, the body gear is centered and body
gear steering is deactivated.
Brake System
Each main gear wheel has a multiple disc carbon brake. The nose wheels have no
brakes. The brake system includes:
　
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