Pilot’s Manual
PM-126A 3-9
LANDING GEAR SYSTEM
The landing gear is hydraulically retractable, tricycle gear with airhydraulic
shock strut-type nose and main gear. The main gear struts are
of a trailing-link design. The main gear has dual wheels and brakes on
each strut. Each main gear wheel is equipped with three fusible plugs
which will melt and release tire pressure in the event wheel temperature
reaches 390° F (199° C). The brake system incorporates four
hydraulically-actuated multi-disc carbon brakes with an integral antiskid
system. The nose gear utilizes a chined tire to prevent splashing
into the engine inlet. Nose wheel steering is electrically powered and
controlled by the nose wheel steering controller. Hydraulic pressure for
gear retraction and extension is transmitted by a system of tubing, hoses,
and actuating cylinders, and is electrically controlled by switches,
relays, and solenoid valves. Emergency extension can be accomplished
by mechanical landing gear “free-fall” in case of hydraulic or electrical
system failure. Two doors enclose each main gear after retraction. The
inboard doors are hydraulically operated and the outboard doors are
mechanically operated by linkage connected to the main gear struts.
The nose gear doors operate mechanically with linkage attached to the
nose gear shock strut.
LANDING GEAR CONTROL SWITCH
The Landing Gear Control switch (GEAR/HYD panel) is a lever-lock
type switch and must be pulled aft before selecting the UP or DN position.
The switch controls the position of the gear selector valve and the
door selector valve through gear and door position-sensing switches.
Electrical power for the control circuits is 28-vdc supplied through the
3-amp GEAR circuit breaker on the pilot’s circuit breaker panel
(GEAR/HAYDRAULICS group). The landing gear control circuits are
powered from the EMER BATT.
Landing gear retraction cycle: When the Landing Gear Control switch
is placed in the UP position and the main gear weight-on-wheels
switches are in the air mode, the following sequence of events will occur:
1. 28-vdc will be applied to the “open” solenoid of the door selector
valve and hydraulic pressure will be applied to both inboard
main gear door actuators and the inboard door uplocks.
2. When the inboard main gear doors open, door open switches
will complete a circuit from the Landing Gear Control switch to
the “up” solenoid of the gear selector valve. Hydraulic pressure
will be applied to the main and nose gear actuators and the gear
will retract.
Pilot’s Manual
3-10 PM-126A
3. When the main gear retract, gear up switches will complete a
circuit from the Landing Gear Control switch to the “close”
solenoid of the door selector valves. Hydraulic pressure will be
applied to the inboard main gear door actuators to raise the
gear doors. Pressure will remain on the main gear actuators
until the doors are in the locked position.
4. The gear doors are locked into position by a hook/roller locking
mechanism.
The normal retraction cycle takes approximately 11 seconds to complete
with one or two main pumps. The auxiliary pump cycle will take
about 18 seconds to complete.
Landing gear extension cycle: When the Landing Gear Control switch
is placed in the DN position the following sequence of events will
occur:
1. 28-vdc will be applied to the “open” solenoid of the door selector
valve and hydraulic pressure will be applied to both inboard
main gear door uplock actuators. Simultaneously, pressure is
applied to the gear up actuator to hold gear in up position while
main landing gear inboard doors open.
2. When the main gear doors open, door open switches will complete
a circuit from the Landing Gear Control switch to the
“down” solenoid of the gear selector valve. Hydraulic pressure
will simultaneously be applied to release the nose gear uplock,
apply pressure to the main and nose gear actuators, and extend
all three landing gear.
3. When the main gear are full down, gear down switches will
complete a circuit from the Landing Gear Control switch to the
“close” solenoid of the door selector valve. Hydraulic pressure
will be applied to the inboard main gear door actuators to raise
the gear doors.
4. The main gear doors are locked into the retracted position by a
hook/roller locking mechanism.
The normal extension cycle takes approximately 11 seconds to complete
with one or two main pumps. The auxiliary pump cycle will take
about 35 seconds to complete.
Pilot’s Manual
　
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