52-32-00
 ALL  ú ú 02 Page 7 ú Feb 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 E.  The master latch lock mechanism is operated by either of two manual handles located in the same housing. One handle is operated from outside the airplane, the other, from inside. A retainer is provided to secure the inside handle to prevent the door from being unlocked and manually opened from outside the airplane when the airplane interior next to the door is in the passenger configuration. Before either the internal or external handle can be operated the retainer must be opened. Attempting to open the external handle without first opening the retainer could shear the shear pin in the external handle.
 F.  A compression spring is installed in the master latch lock handle housing to force the exterior handle open if not securely latched closed. The spring contacts the handle just prior to closed and latched position and is compressed when handle is latched.
 G.  The aft pressure relief door operates a door warning switch which illuminates the side cargo door warning indication on EICAS in the control cabin when the pressure relief door is not closed. Refer to 52-71-00/001, Door Warning System - D&O for more information on the side cargo door warning switch indication.
 H.  The pressure relief door shrouds prevent the doors from being driven closed by the out-rushing air flow through the opening in the event that the master lock handle is in the unlocked position when airplane pressurization begins. The pressure relief doors prevent airplane pressurization if the side cargo door is not correctly locked.
 4.  Latch Mechanism (Fig. 2)
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 A.  The latch mechanism is a system of latch cams, torque tubes and linkages driven by an electrically powered actuator with auxiliary manual drive. Ten latch cams along the lower edge of the door and two midway up the door (one at each edge) engage latch pins on the door sill and side frames to latch the door closed.
 B.  The latch actuator is identical to the hook actuators and consists of a 3-phase, 115-v AC electric motor coupled to a reduction gearbox with splined output shafts extending from either side. The actuator is installed in-line with the latch torque tube.
 C.  The ten lower latch cams are installed on five short shafts at the bottom of the door. The two midspan latch cams are installed on the ends of separate torque tubes midway up the door. The five lower and two midspan latch shafts are connected by linkages to a common latch torque tube which is driven by the latch actuator.
 5.  Hook Mechanism (Fig. 2)
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 A.  The hook mechanism consists of two mechanically independent mechanisms, each operating a hook on one side of the door near the bottom. The two mechanisms contain the same components consisting of hook actuator, torque tube, hook, restraint arm, and restraint solenoid.
 B.  The two hooks engage hook pins on the door frames as the door closes to pull the door completely closed and ensure correct alignment of the latch cams. The hooks are installed on the ends of short shafts which are connected by linkages to the hook torque tube driven by the hook actuator.
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 52-32-00
 ALL  ú ú 03 Page 8 ú Feb 15/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 C.  The two hook actuators are identical to the latch actuator and consist of a 3-phase, 115-v AC electric motor coupled to a reduction gearbox with splined output shafts extending from either side. One of the actuator output shafts is connected to the appropriate hook torque tube.
 D.  The hook torque tubes are prevented from rotating open by restraint arms which engage stop fittings on the torque tubes. The restraint solenoid lifts the restraint arm to clear the stop fittings to allow the torque tubes to rotate to open the door. The restraint arm rides over the stops as the torque tube rotates to close the door.
 6.  Lift Mechanism (Fig. 2)______________
 A.  The door lift mechanism is installed above the door, inside the ceiling cavity, and includes a lift power unit, two gearbox and brake assemblies, four rotary actuators and two actuator arms. The two rotary actuator arms are connected by links to fittings on the door just below hinge line.
 B.  The lift power unit drives the two rotary actuator arms through separate but identical drive components, including rotary actuators, gearbox and brake assembly and torque tubes. Each arm is installed on a splined shaft between two rotary actuators which are connected by a torque tube to the gearbox and brake assembly and then to the power unit. An interconnect torque tube is installed between the two gearboxes to keep both rotary actuator arms synchronized. Structural upstops and downstops are installed at each actuator arm to limit travel in the event electrical limit switches fail to shutoff the power unit.
　
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