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 6.  Push-Pull Cam Actuator (Fig. 1)
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 A.  The push-pull cam actuator is designed to pull the door against the seals when closing so that the latch actuators can latch the door. When opening, it is designed to push the door away from the seal even if the door is restrained by ice.
 B.  The actuator has an AC motor, a magnetic brake, thermal overload protection, a gearbox and jackscrew with self-aligning end fittings, manual drive input, and limit switches to control the extend and retract strokes. Three-phase electrical power is supplied from the main deck cargo handling bus.
 C.  The push-pull cam actuator extends and retracts through a stroke of
 4.50 inches. Non-jamming end stops in the actuator are designed to absorb the impact force if the actuator overruns the limit switch position and prevent load on the jackscrew threads. The actuator can be operated electrically or manually with the torque wrench.
 D.  The push-pull cam actuator extends and retracts through a stroke of 4.50 inches. A non-jamming end stops in the actuator are designed to absorb the impact force if the actuator overruns the limit switch position and prevent load on the jackscrew threads. The actuator can be operated electrically or manually with the torque wrench.
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 52-31-00
 ALL  ú ú 02 Page 9 ú Feb 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 7.  Nose Cargo Door Position Indication
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 A.  Indication lights are available at the loadmaster's station for visual indication of the door open/closed status. The indication lights consist of 32 lights, 16 green LATCH and 16 amber NOT LCHD, on the NOSE CARGO DOOR LATCH ANNUNCIATOR panel and two green CLOSED lights and two amber NOT CLSD lights on the NOSE CARGO DOOR CLOSED ANNUCIATION panel. The green LATCHED lights come on when the door is closed and fully latched. The amber NOT LCHD lights come on when the door is closed and the latches are not-fully latched. Two green CLOSED lights on the NOSE CARGO DOOR CLOSED ANNUNCIATOR panel come on when the nose cargo door is fully faired with the fuelage. The two amber NOT CLSD lights come on when the door is not fully closed. For information about the door warning indication (AMM 52-71-00/001).
 8.  Latch Actuator Test Panel (Fig. 1)
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 A.  The latch actuator test panel is a built-in-test-equipment (BITE) panel installed on the opposite side of the loadmaster's station. The panel is used to isolate a defective latch actuator within the system. The panel has two test lights, three momentary test switches and a 16-position latch selector switch.
 9.  Pressure Switch and Isolation Relay
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 A.  A pressure switch and isolation relay are installed below the actuator test panel. They remove all electrical power from the door control system when the airplane is pressurized or the pressure difference between cabin and ambient is more than 12 inches water (0.433 psi).
 10. Operation (Fig. 2)
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 A.  Functional Description
 (1)  
The operation of the nose cargo door is accomplished through the combined function of a drive unit, push-pull cam actuator and 16 door latch actuators. Control for these units is located on the nose door control and light panel, H121, at the loadmaster's control station.

 (2)  
By simultaneously holding the SYSTEM POWER switch in the ON position and the DOOR CONTROL switch in the OPEN position, the white POWER ON light will illuminate and the door LATCHES CLOSED light will extinguish as soon as any one of the 16 latch pins start to withdraw from the partial latch fittings. Simultaneously, as each of the 16 latch actuators start withdrawal, the green LATCHED lights on the NOSE CARGO DOOR ANNUNCIATOR panel will extinguish and the amber NOT LCHD lights will illuminate. Also, the caution message DOOR NOSE CARGO shows on the EICAS in the flight deck. When all latch pins are retracted, sequence switches in the latch actuators close to allow power to the push-pull cam actuator. The push-pull cam actuator energizes and drives the push-pull cam to open the door approximately 1.3 inches measured at the centerline of the cam roller. When the push-pull actuator is fully extended, a sequence switch within the actuator de-energizes the actuator and allows current to flow to the door drive unit which drives both linear actuators through flexible drive shafts. When the door reaches the full open position a sequence switch within the drive unit shuts off the drive unit and illuminates the blue DOOR UP light.
　
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