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pressure lines and return hydraulic fluid present in the gear
extend, gear retract and gear door lines and actuators to the
system reservoir. This action prevents any hydraulic lock in
the landing gear actuators. Nitrogen then pressurizes the
OPERATING MANUAL
2A-32-00 PRODUCTION AIRCRAFT SYSTEMS
Page 18
January 31/02
Revision 6
unlock port of the three gear uplock actuators, the open port
of the three door actuators and the extend port of the three
landing gear actuators.
(d) Dump Valve Reset Handle
A reset handle (D-ring), shown in Figure 9, is located on the
inside of the copilot side console and labeled EMERGENCY
LANDING GEAR DUMP VALVE RESET. The D-ring is
mechanically connected to the hydraulic system dump
valves. Pulling the D-ring returns the dump valves to the
normal hydraulic system setting. If emergency extension of
the landing gear with the pressurized nitrogen bottle has
been satisfactorily completed, the landing gear would
normally be left extended until a landing could be made. If
however, the landing gear must be retracted and hydraulic
fluid and Combined or Utility system pressure is available,
resetting the dump valves will allow retraction of the landing
gear.
(2) Landing Gear Emergency Extension Sequence
(a) Landing gear lever is placed in DOWN position
(b) Red light in landing gear lever handle is illuminated
(c) EMER LDG GEAR T-handle is pulled to full limit of travel
(d) Compressed nitrogen is released to landing gear dump
valves
(e) Dump valves isolate landing gear extend lines from
remainder of hydraulic system and open returns for hydraulic
fluid in actuators to hydraulic reservoirs
(f) Pressurized nitrogen is routed to OPEN side of landing gear
door actuators, UNLOCK side of landing gear uplock
actuators, EXTEND side of main landing gear sidebrace
actuators and nose landing gear extend / retract actuator
(g) Landing gear doors open
(h) Uplock actuators unlock
(i) Landing gear extends down and locks
(j) Three green DOWN AND LOCKED lights on landing gear
control panel illuminate
(k) Red light in landing gear lever handle extinguishes
(l) Landing gear doors remain open
D. Nutcracker System
The nutcracker (squat) switch system provides AIR or GROUND sensing to
aircraft systems and components. A nutcracker switch is installed on each
landing gear. The nutcracker switch contacts are depressed when the
landing gear oleo-pneumatic struts are compressed by the weight of the
aircraft on the ground. When the aircraft is in flight, the struts extend,
releasing pressure on the nutcracker switches and opening the switch
contacts. The nutcracker switch system is connected to seventeen relays.
Circuits may be opened or closed corresponding to AIR or GROUND states
of operation by wiring systems and components through the nutcracker
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-32-00
Page 19
January 31/02
Revision 6
switch relays.
The left and right main landing gear nutcracker switch relays are powered
by the Essential DC bus. The nose gear nutcracker switch relay is powered
by the Emergency DC bus. The main gear nutcracker switches are
incorporated into a test circuit that verifies switch integrity. (The nose
landing gear nutcracker switch is not tested.) The test switch is located on
the center pedestal aft of the throttle quadrant. Each nutcracker switch has
a dedicated circuit breaker. If a nutcracker switch fails in the ground
(closed) position, pulling the respective circuit breaker will change the
switch input to relays to the air position.
Nutcracker switch inputs from the main landing gear control the landing
gear lever safety lock solenoid and the nose landing gear nutcracker switch
weight-on-wheels signal is necessary for nosewheel steering. For a list of
nutcracker system relay inputs to aircraft systems and components, see
the following table.
Ground Mode (Weight on Wheels) Flight Mode (Weight off Wheels)
Thrust reverser operation
Engine ground idle
Ground spoiler operation
APU control
Air flow control
Cockpit clocks
FMCS
EDS
Autopilot
Cockpit voice recorder
ILS
Engine starting
Speedbrake / Flap alarm
Cabin pressure control
EICAS DAU / FWC #1
EICAS DAU / FWC #2
G-meter
Stall barrier
Thrust reverser REVERSE ALERT light
Engine flight idle
Angle of attack indication
Gear lever downlock solenoid pin retract
Pitot heat
VHF nav
Brake-by-wire
Flight data recorder
NOTE:
Failure of the nutcracker system will result in
　
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