(7)  
Operating switch No. 1 to CLOSE completes 28 volts dc through the canopy position A switch to the POS 2 winding of the control valve. The valve then goes to the POS 2 position, operates the internal switches and completes 28 volts dc to the shutoff valve. Hydraulic pressure is again connected to the "close" lines of the actuator and the door closes. When the latch hooks contact the latch pins on the sill the hooks rotate slightly to move the latch actuator overcenter so that it may operate. The latch actuator then continues the rotation of the latch hooks around the latch pins to pull the door completely closed. When the door is closed and switch No. 1 is released, 28 volts dc is connected through the door position switch to the control valve to ensure the control valve is held in POS 2 and the other internal switch connects to the POS 1 winding for the next open sequence. Locking the door with the external control handle insert lockpins across the latch hooks to prevent the door from being accidentally opened and the door lock switch shuts off electrical power to the main cargo door switches No. 1 and 2. The main cargo door unlocked light will extinguish when the door is closed and locked. The main cargo door warning light will extinguish and the lights at latch viewing windows No. 2 and 7 will illuminate when the handle is locked. Refer to Door Warning System for operation of additional door warning circuits.

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52-32-0 Page 20  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Aug 15/72 

C.  Manual Operation with Handpump
(1)  
Manual operation of the main cargo door requires all electrical power be removed from the system (main cargo door circuit breaker pulled). It is assumed hydraulic system B is inoperable.

CAUTION:  CONTROL VALVE MOTOR BURNOUT MAY OCCUR IF CONTROL VALVE IS POSITIONED WHEN ELECTRICAL POWER IS ON THE SYSTEM. ENSURE MAIN CARGO DOOR CIRCUIT BREAKER IS OPEN AND SUITABLY TAGGED BEFORE MANUAL OPERATION.

(2)  
The cargo door is first unlocked by pulling on the external lock handle. The motor-operated control valve in the left wheel well must be positioned to POS 1. A manual override is on the control valve. The main cargo door handpump in the left wheel well is then operated to raise the door. Operation of the lift and latch actuators and associated mechanisms is similar to that described under normal operation. Approximately 45 strokes of the pump are required to raise the door to the canopy position. The door should be raised slightly above the canopy position; the manual override on the control valve is then positioned to POS 2 to release the hydraulic lock. The door then lowers until the internal ram lock of the lift actuator stops the door just below the canopy position. The door is raised to the full open position by positioning the control valve override to POS 1 and operating the handpump for approximately 25 strokes. A hydraulic lock holds the door open as long as the control valve is left in POS 1.

(3)  
The door is closed from the full open position by operating the control valve override to POS 2 and operating the handpump. After the door passes top dead center, door weight will drive the door to the canopy position where the internal ram lock in the lift actuator will stop the door. Further operation of the handpump will unlock the lift actuator's internal ram lock and allow the door to lower. The return line flow limiter controls the rate that the cargo door closes. Additional pumping is not required until the door is resting on the latch pins. The door may be stopped in any position by positioning the control valve override to  POS 1. Positioning the control valve override to POS 2 allows the door to continue closing. The door is latched by operating the handpump. Hydraulic pressure then operates the latch actuator which causes the latch hooks to rotate, engage the latch pins and pull the door closed. The door should then be locked by operating the external lock handle. The control valve should remain in POS 2 after it is locked closed.

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Feb 01/76  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  52-32-0 Page 21 

D.  Emergency External Operation
(1)  In the event that a system malfunction prevents the door from being opened normally or with the manual handpump, panels on the exterior of the door may be removed for access to the lock and latch mechanisms. Normally the lockpins can be retracted using the unlocking handle; if not, they will have to be levered to a retracted position through the access opening. Similarly the latches can be levered to the unlatched position. Once the door is unlatched it may be raised with a hoist or crane.
NOTE:  If a hydraulic lock in the system prevents unlatching, open a hydraulic line to relieve pressure. 
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