(i)  
As the hooks move from the closed position, the hook closed switch moves to the hook not closed position. As the door begins to open, the door closed switch moves to the door not closed position. These two switches enable door operation to be stopped or reversed as door opening progresses. When the hooks are rotated fully open (door open approximately 3 inches), the hook position switch is actuated to the hook unsafe position. This energizes the hook position relay which removes power from the hook power unit and transfers power to the lift power unit to open the door.

 (j)  
When the door reaches the full open position, the door up switch is actuated to the up position. This removes power from the lift actuator and de-energizes the door open control circuit. The hook position relay remains energizes and all other sequence switches are positioned to enable the door to be closed electrically.

 (2)  
Close door electrically.

 (a)  
When the cargo door control switch is placed in the close position, control power is provided through the energized hook position relay to the lift actuator. Power is also supplied to the brake release function of the hook actuator to allow the hooks to rotate when they contact the hook pins on closing. As the door moves away from the full up position, the door up switch moves to the not up position to permit door operation to be stopped or reversed at any time.

 (b)  
As the hooks contact hook pins on door closing they are mechanically rotated toward the closed position. As the hooks begin to move, the hook position switch moves to the safe position and de-energizes the hook position relay. This removes power from the lift actuator and transfers power to the hook actuator through the hook closed switch.

 (c)  
When the hooks reach their fully closed position, the hook closed switch is actuated to the hook closed position to remove power from the hook actuator. At the same time, the door has reached the fully closed position and actuates the door closed switch to the door closed position. Control power is then supplied through the hook closed and latch closed switches to the latch actuator.

 (d)  
The door closed switch also sends a signal to the door warning system. This signal shows the door warning system that the door is closed.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400 MAINTENANCE MANUAL
 (e)  
The latch actuator moves the latch cams away from the open position. This actuates both midspan latch open switches and the latch open switch to the not open position. The latch open switch then supplies a control circuit to the latch actuator. Because of this, you can reverse the operation of the door, if necessary.

 (f)  
When the latches reach the fully closed position, the latch closed switch is actuated to the latch closed position to remove power from the latch actuator and de-energize the door closed control circuit.

 (g)  
At the same time, the latch closed switch makes the green LATCHES CLOSED light on the door operators control panel go on. This shows the door operator that the door is closed and ready to be locked.

 (h)  
The door latched switch operates when the latches close. The switch sends a signal to the door warning system that the door is latched.

 (i)  
When the master latch lock handle is moved up and latched into its housing, the latch lock sectors extend to interfere with the latch cams to lock them closed. As the lock sectors extend, the master latch lock switch moves to the latch locked position to prevent electrical operation of the door.

 (j)  
When the master latch lock handle is rotated fully up and locked, the pressure relief doors in the cargo door close and actuate the door warning switch. The door warning switch sends a signal to the door warning system that the door is locked.

 (k)  
The door warning system gets signals from the door closed, door latched, and door warning switches. When the door warning system senses that the door is closed, latched and locked the cargo door warning message does not show on EICAS. At the same time, the master latch lock switch makes the green LATCHES CLOSED light on the door operators control panel go out. This shows the door operator that the door is closed and locked.

 (l)  
The door warning system gets a signal from the door warning switch. When the door warning system senses that the door is locked, the cargo door warning message does not show on EICAS.
　
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