General
The alternate extend power pack pressurizes hydraulic fluid from the center hydraulic system.
Pressure goes to the MLG and the NLG selector/bypass valves. If the selector valve is in the UP or OFF position, the bypass valve moves to the BYPASS position to let the gear extend. See the landing gear control section for more information about the landing gear selector/bypass valves (SECTION 32-31).
The MLG and NLG alternate extend components operate the same. Each MLG and the NLG have these components:
*
Landing gear door release/safety valve module

*
Landing gear alternate uplock release actuator.

There is one alternate extend hydraulic pressure switch located in the NLG wheel well.
Landing Gear Door Release/Safety Valve Module
Alternate extend pressure extends the door release actuator. This actuator releases the landing gear door which then opens by gravity and airloads.
As the door release actuator extends, the safety valve moves to the SAFE position. The safety valve is latched in the SAFE position.
EFFECTIVITY
BEJ ALL

After it extends, the door release actuator sends pressure to the landing gear alternate uplock release actuator.
Landing Gear Alternate Uplock Release Actuator
The landing gear alternate uplock release actuator extends to unlock the landing gear uplock. This permits gravity and airloads to extend the gear. The tires may contact the door during alternate extension.
Alternate Extend Hydraulic Pressure Switch
After all doors and gear are unlocked, hydraulic pressure in the alternate extension system increases. When the pressure gets to 2100 psi, the alternate extend hydraulic pressure switch opens. This removes electrical power from the alternate extend control relays. The relays de-energize and remove electrical power from the alternate extend power pack.
Reset
When the alternate extend power pack stops, the alternate uplock release actuator and the door release actuator in the door release/safety valve reset. The springs in the actuators push the hydraulic fluid through the alternate extend power pack and into the oversize supply tube.
32-35-00

Page 37 D633W101-BEJ Sep 05/2002

LANDING GEAR ALTERNATE EXTENSION SYSTEM -FUNCTIONAL DESCRIPTION -HYDRAULIC

The door safety valve in the door release/safety valve module remains in the SAFE position until it is reset. This prevents the door from closing. The door safety valve is reset by an electric signal to the solenoid operated valve. Switches on the P40 and P56 panels, or a switch within the landing gear control lever module provide the reset signal. When the solenoid energizes, the valve permits hydraulic pressure to release the safety valve latch. The reset signal must be made while door close hydraulic pressure is available. When the valve moves to the NORMAL position, the door closes.
EFFECTIVITY BEJ ALL  32-35-00 
Page 38 
D633W101-BEJ  Sep 05/2002 

LANDING GEAR ALTERNATE EXTENSION SYSTEM -FUNCTIONAL DESCRIPTION -HYDRAULIC

EFFECTIVITY BEJ ALL  32-35-00 
Page 39 
D633W101-BEJ  Sep 05/2002 

LANDING GEAR ALTERNATE EXTENSION SYSTEM -LANDING GEAR DOOR CLOSE OPERATION

General
You can close the landing gear doors with the door close switches or with the landing gear lever. The center hydraulic system supplies the pressure to close the landing gear doors.
MLG and NLG gear door close operation is almost the same.
Door Close Operation
You close the two main landing gear doors at the same time with switches on the P56 wheel well electrical service panel.
You close the nose landing gear doors with switches on the P40 service and APU shutdown panel.
The landing gear lever closes all the landing gear doors only after the gear have retracted. The landing gear door close signal from the landing gear lever goes through a five second time delay relay in the P320 ground handling/service distribution panel. When you move the landing gear lever to the UP position, the solenoids in the door release/safety valve modules get power five seconds later. This delay gives the selector valves time to move to the UP position. This prevents the safety valve from accidental movement to the NORMAL position before the selector valve has time to move. The delay makes sure the door release/safety valve modules are reset by the lever only after the gear retract.
For any door close signal, power from the 28v dc left main bus goes to the solenoid valves in the landing gear door release/ safety valve modules.
To close the doors, the door close signal must be made at the same time door close hydraulic pressure is available.
Training Information Point
When you use the switches on the P56 panel, the main landing gear doors close in approximately 10 seconds.
WARNING: MAKE SURE THE AREA AROUND THE DOORS FOR THE MAIN LANDING GEAR IS CLEAR OF PERSONS AND EQUIPMENT. THE DOORS CLOSE QUICKLY AND CAN CAUSE INJURY TO PERSONS OR DAMAGE TO EQUIPMENT.
　
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