01. boeing 727 ata 32 - landing gear

LINE AND BASE MAINTENACE TRAINING
LANDING GEAR
B727-200
AIRWAYS CONSULTORIA AERONÁUTICA LTDA

AIRWAYS TREINAMENTOS LANDING GEAR
32.2
MATERIAL DIDÁTICO
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AIRWAYS CONSULTORIA AERONÁUTICA LTDA.

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T
TR
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EM
M D
DE
E P
PO
OU
US
SO
O
C
CA
AP
PÍ
ÍT
TU
UL
LO
O 3
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2

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LANDING GEAR - DESCRIPTION AND OPERATION
1 . General
A.The landing gear supports the airplane during ground operations, cushions impact on landing, dampens
vibrations and absorbs shock when the airplane is taxied or towed. Two main gears and one nose gear are
used (Fig. 1).
B.Each main gear is located behind the rear wing spar, just outboard of the body. The nose gear is located below
the aft portion of the control cabin. Side struts and drag struts stabilize the main gear laterally and longitudinally
(Fig. 2). The nose gear is steerable, and is braced longitudinally by a hinged drag brace (Fig. 3). The main and
nose gears have dual wheels, and all wheels are provided with hydraulic brakes, action modulated by an antiskid
system. A retractable tailskid is mounted on the rear fuselage to protect the aft end of the airplane from damage
should the nose be raised excessively high when the airplane is on the ground with the ventral stairs retracted.
B. Retraction and extension of the gear is by hydraulic power, with a manual extension system for lowering the
gear when hydraulic power is not available. The landing gear is controlled by a single control handle mounted on
the pilots' instrument panel. Cables from a drum actuated by the control lever, transfer motion to a selector valve
that directs hydraulic pressure for gear actuation.
C. When the control handle is moved to the up position, the landingear doors open, the gear retracts and all doors
close. When the control handle is moved to the down position, all landing gear doors open, the gear extends and
the wheel well doors close. Wing doors remain open.
With the control handle in the off position hydraulic pressure is released from all landing gear hydraulic lines and
actuators, and the gear is held in the extended or retracted position by the mechanical locks.
D. A crank and cable system for main gear manual extension unlocks the doors first, and then unlocks the gear,
which falls to the extended position by gravity. Operation for nose gear manual extension unlocks the gear only.

32.7
Main gear doors are pushed fully open by the weight of the gear acting on a safety bar mechanism. The nose gear
doors are opened, and then closed, by mechanical linkage when the nose gear falls to the extended position.
Final operation of the manual extension system engages the down locks to lock the gears in the extended
position. Main landing gear doors remain open after manual extension of the gear.
2 . Mechanical fuse points.
A. Mechanical fuse points are connections with fasteners designed to fail first under excessive shock loads. Fuse
points are designed to minimize damage to primary structure if attached components are subjected to severe
impact loads. The following table lists those connections in landing gear systems, and the section of the chapter
where additional coverage will be found.

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G
GE
EA
AR
R L
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OC
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PI
IN
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S

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32.12
LANDING GEAR ELECTRICAL/ELECTRONIC MODULE – DESCRIPTIO AND OPERATION
1 . General
A. The landing gear electrical control and safety relays necessary for operation of the landing gear, tailskid and
brake antiskid systems are grouped together in a module for ease of maintenance. The control and safety relays
set up sequences and tie in all the safety sensors/switches during operation of gear, tailskid and brake antiskid
systems. The function of each relay is described in the section of the manual covering the system in which the
relay is a component.
2 . LANDING GEAR ELECTRICAL/ELECTRONIC MODULE
B. The landing gear electrical/electronic module is a rack mounted box containing the control and safety relays,
solid-state circuits and necessary wiring and connectors. The module is located in the E5-1 electrical/electronic
equipment compartment (Fig. 1).

32.13

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32.15
LANDING GEAR SAFETY SENSOR – DESCRIPTION AND OPERATION
1 . GENERAL
A. Certain systems of the airplane require electrical control depending upon the condition of the airplane, whether
airborne or on the ground (Fig. 1). The main gear shock strut extended or compressed condition is indicated by
the landing gear ground and air safety sensors (proximity switches). The nose landing gear shock strut extended
or compressed condition is indicated by a nose gear safety switch in the lower nose compartment. The safety
sensors transmit signals to solid-state circuits and relays in the landing gear electrical module to provide "air" or
"ground" control of systems or components. Some circuits are activated when the airplane is in the air while others
are activated when the airplane is on the ground. The landing gear control lever lock system is controlled by safety
relay energized by a and ground safety sensor. The antiskid system is controlled by air and ground safety
sensors. Some other airplane systems and components controlled by air-ground sensing are: aural warning,
automatic speed brake, takeoff warning, autopilot gyros, stall warning, standby electrical power, APU fuel valve,
APU fire warning, voice recorder, air conditioning system, wing anti-ice, drain mast heater, speed command
system, and cabin pressurization control system.
B. An air sensing test switch and a ground sensing test switch on the electrical module are used to simulate an
airplane-in-air condition. The switches must be pressed and held down to simulate the airplane-in-air condition.
When the switches are released, the systems return to the airplane-on-ground condition. To test air critical
systems, press and hold the ground sensing test switch. To test ground critical systems, press and hold the air
sensing test switch (Fig. 2). When the airplane-in-air condition is simulated, certain precautions regarding the
systems listed in Fig. 2 should be observed.

32.16
2 . Landing Gear Safety Sensors
A. The landing gear safety sensors provide signals to solid-state circuits in the landing gear electrical module in
conjunction with the nose gear safety switch to energize or de-energize the safety relays depending upon whether
the airplane is airborne or on the ground. The safety sensors are mounted near the ground speed brake valve
above the left main gear trunnion (Fig. 3). The safety sensors are proximity switches that sense the presence or
absence of a ferrous metal actuator. A double-paddle metal actuator to activate the safety sensors is connected to
the speed brake valve linkage. The speed brake valve linkage is operated through a combination of pushrods and
bellcranks by the extension and compression movement of the shock strut. Linkage movement positions the
metallic actuator near or away from the respective sensor to provide the appropriate signal to the landing gear
electrical module.

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01. boeing 727 ata 32 - landing gear

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