2-8. LANDING GEAR SYSTEM.
The retractable tricycle landing gear is electrically controlled and hydraulically actuated. The landing gear-assem-
blies 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 28V DC motor, a gear selector valve and
solenoid, a two section luid reservoir, ilter screens, gear-up pressure switch and low luid level sensor. Engine
bleed air, regulated to 18 to 20 psi, is plumbed into the power pack reservoir, and the system ill reservoir to prevent
cavitations of the pump. The luid level sensor activates an amber caution annunciator, placarded HYD FLUID LOW
located in the caution/advisory annunciator panel, whenever the luid level in the power pack is low. The annuncia-
tor is tested by pressing the HYD FLUID SENSOR TEST switch located on pilot s subpanel (Fig. 2-11). Power for
the hydraulic power pack is supplied through a landing gear motor relay and a 60-ampere circuit breaker located
under the loorboard 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 (Fig. 2-12) and the down
lock switches. A time delay module which senses operation voltage through a 5-ampere circuit breaker protects
the power pack motor. Both are located beneath the aisle way loorboards, forward of the main spar. Landing gear
extension or retraction is normally accomplished in 6 to 7 seconds. Voltage to the power pack is terminated after the
fully extended or retracted position is reached. If electrical power has not terminated within 14 seconds, 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 main landing gear is 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 power pack pressure switch and an accumulator that is
pre-charged with nitrogen to 800 ± 50psi control the pressure. Gear doors are opened and closed through a me-
chanical 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, illed with
compressed nitrogen and hydraulic luid, 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 pilot s subpanel (Fig. 2-11). The control switch
and associated relay circuits are protected by a 2-ampere circuit breaker placarded LANDING GEAR CONTROL
b. Landing Gear Down Position Annunciators. Three, individual, green GEAR DOWN annunciators located
on the left subpanel provide visual indication of the landing gear position. Testing of the annunciators is accom-
plished 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 (Fig. 2-12).
c. Landing Gear Position Warning Annunciators. Two red parallel-wired annunciators located in the LDG
GEAR CONTROL switch handle, illuminate to show that the gear is in transit or unlocked. The red annunciator
in the handle also illuminates when the landing gear warning horn is actuated. Both red annunciators 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 panel
d. Landing Gear Warning Annunciator Test Switch. A test switch, placarded HDL LT TEST , is located on
the pilot s subpanel (Fig. 2-11). Failure of the landing gear handle to illuminate red, when this test switch is pressed,
indicates two defective bulbs or a circuit fault. A 5-ampere circuit breaker, placarded LANDING GEAR HORN , on
the overhead circuit breaker panel (Fig. 2-12), protects the circuit.
e. Landing Gear Warning System. The landing gear warning system is provided to warn the pilot that the
landing gear is not down and locked during speciic light regimes. Various warning modes result, depending upon
the position of the laps.
At airspeeds above 140 KIAS with laps in the UP or APPROACH position and either or both power levers retarded
below approximately 84% N., the landing gear switch handle annunciator will illuminate. An altitude-sensing switch,
provided to silence the landing gear warning horn when above 12,500 feet, automatically silences the horn. This
prevents the horn from sounding above 12,500 feet when either power lever is pulled back, provided the laps are
at the approach position or above.
At airspeeds below 140 KIAS with laps in the UP or APPROACH positions with either or both POWER levers re-
tarded below approximately 84% N 1 , the warning horn will sound and the landing gear switch handle annunciators
will illuminate. The horn can be silenced by actuating the GEAR WARN SILENCE switch located adjacent to the
landing gear switch handle, to the up position. However, the annunciators in the landing gear switch handle cannot
be cancelled. The gear warning silence switch is a magnetically held switch. Once actuated it will stay in the up