2-8. LANDING GEAR SYSTEM D2 T .
electrically controlled and hydraulically actuated. The
landing gear assemblies are extended and retracted
by a hydraulic power pack, located in the left wing
center section, forward of the main spar. The power
pack consists primarily of a hydraulic pump, a 28 Vdc
motor, a gear selector valve and solenoid, a two
section fluid reservoir, filter screens, gear up pressure
switch and low fluid level sensor. Engine bleed air,
regulated to 18 to 20 psi, is plumbed into the power
pack reservoir, and the system fill reservoir to prevent
cavitation of the pump. The fluid level sensor activates
a yellow caution light, placarded HYD FLUID LOW, on
the annunciator panel, whenever the fluid level in the
power pack is low. The annunciator is tested by
pressing the HYD FLUID SENSOR TEST switch
located on pilot's subpanel. Refer to Figure 2-8.
Power for the power pack is supplied from the
No. 5 dual fed buss, through a landing gear motor
relay and a 60-ampere circuit breaker located under
the floor board forward of the main spar. The motor
relay is energized by power furnished through a
2-ampere LANDING GEAR CONTROL circuit breaker
located on the overhead circuit breaker panel, and the
downlock switches. The power pack motor is
protected by a time delay module, which senses
operation voltage through a 5-ampere circuit breaker.
Both are located beneath the aisle way floorboards
forward of the main spar. Landing gear extension or
retraction is normally accomplished in 5 to 6 seconds.
Voltage to the power pack is terminated after the fully
(approximately 23 seconds). If electrical power has
not terminated after the normal extension or retraction
time lapse, a relay and 2-ampere landing gear circuit
breaker will open and electrical power to the system
power pack will be interrupted.
The landing gear system utilizes folding braces,
called drag legs that lock in place when the gear is
fully extended. The nose landing gear actuator
incorporates an internal down-lock to hold the gear in
the fully extended position. However, the two main
landing gears are held in the fully extended position by
mechanical hook and pin locks. The landing gear is
held in the up position by hydraulic pressure.
The pressure is controlled by the power pack
pressure switch and an accumulator that is pre-
charged with nitrogen to 800 ± 50 psi. Gear doors are
opened and closed through a mechanical linkage
connected to the landing gear. The nose wheel
steering mechanism is automatically centered and the
rudder pedals relieved of the steering load when the
landing gear is retracted. Air-oil type shock struts,
filled with compressed air and hydraulic fluid, are
incorporated with the landing gear.
a. Landing Gear Control Switch. Landing
gear system operation is controlled by a manually
actuated wheel-shaped switch, placarded LDG GEAR
CONTROL UP / DN on the left subpanel. The control
switch and associated relay circuits are protected by a
2-ampere circuit breaker, placarded LANDING GEAR
CONTROL, located on the overhead circuit breaker
b. Landing Gear Down Position-Indicator
Lights. Landing gear down position is indicated by
three green lights on the left subpanel, placarded
GEAR DOWN D2 T1 . Refer to Figure 2-8, Sheets 1
and 2. Visual indication of the landing gear position is
provided by individual green GEAR DOWN indicator
lights, placarded NOSE L / R, on the left subpanel.
T2 . Refer to Figure 2-8, Sheet 3. Testing of the
indicator lights is accomplished by pressing the
annunciator test switch. The circuit is protected by a
5-ampere circuit breaker, placarded LANDING GEAR
IND, on the overhead circuit breaker panel.
c. Landing Gear Position Warning Lights.
Two red parallel-wired indicator lights located in the
LDG GEAR CONTROL D2 T1 or LDG GEAR CONTR
T2 switch handle illuminate to show that the gear is in
transit or unlocked. The red lights in the handle also
illuminate when the landing gear warning horn is
actuated. Both red lights indicate the same warning
conditions, but two are provided for a fail-safe
indication in the event one bulb burns out. The circuit
is protected by a 5-ampere circuit breaker, placarded
LANDING GEAR IND, on the overhead circuit breaker
d. Landing Gear Warning Light Test Switch.
A test switch, placarded HDL LT TEST, is located on
the left subpanel. Failure of the landing gear handle to
illuminate red when this test switch is pressed
indicates two defective bulbs or a circuit fault. The
circuit is protected by a 5-ampere circuit breaker,
placarded LANDING GEAR WARN, on the overhead
circuit breaker panel.