2.
SELECT LATCH TO BE TESTED.

3.
DEPRESS DESIRED TEST SWITCH.

4.
FAILURE OF LIGHT TO ILLUMINATE INDICATES LATCH NOT

CLOSED OR OPEN.
5. USE LAMP TEST FOR POWER ON TEST.
Nose Cargo Door Schematic
Figure 2 (Sheet 2)

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747-400
MAINTENANCE MANUAL

 D.  The latch actuator test panel is installed on the right side of the fuselage, opposite of the loadmaster's control station. The panel is used to isolate the defective latch actuator.
 E.  A pressure switch and isolation relay is installed below the actuator test panel. The switch and relay prevent the door from being opened when the airplane is pressurized.
 F.  The door operation is controlled from the nose cargo door light and control panel on the loadmaster's control station. Three phase electrical power is supplied from the cargo handling bus.
 3.  Drive Unit (Fig. 1)
__________
 A.  The drive unit is installed on the centerline in the upper forward area of the door. It has an AC electric motor with a brake, an inertia absorbing device, limit switches, thermal overload protection and a drive housing. The housing contains a reduction gear train with output shafts and connections for the two flexible drive shafts.
 B.  The limit switches that control the linear actuators are incorporated in the drive unit. Therefore, the rotation of the actuators, or the drive unit, when the flexible drive shafts are disconnected can disrupt the synchronization of the actuators. This condition can occur during the manual operation as a result of drive unit replacement.
 C.  The drive unit gives the synchronized rotary output to drive the two linear actuators. Three phase electrical power is supplied from the cargo handling bus.
 4.  Linear Actuators (Fig. 1)
________________
 A.  The two linear actuators are installed on the sides of the door and body structures. Each has an input torque limiter, reduction gearbox, rotating ball nut, ball screw and a no-back unit, and a manual drive input. The ball nuts, when turned by the drive unit, move the door as they travel on the ball scews. The actuators receive a synchronized rotary input from the drive unit and convert it to a synchronized linear output which lifts or lowers the door.
 B.  The ball nut assemblies of the linear actuators are driven by the drive unit through the flexible drive shafts. The ball nuts, when turned by the drive unit, move the door as they travel on the ball scews. The drive shafts mate with the 0.350 square sockets on the forward end of the ball nut assemblies. An equivalent square socket on the aft end allows the manual crank input when the flexible drive shaft is disconnected.
 C.  The input torque limiter prevents actuator overload, either by manual or electrical input.
 D.  An internal no-back brake prevents the ball nut from the backdrive so that the actuators will hold the door in the position.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL

 5.  Latch System (Fig. 1)
____________
 A.  The latch system has 21 latches installed around the circumference of the door frame. They are numbered from the bottom, 1 through 10 left and right, and a single latch 11 on center top. Sixteen latches, 1 through 8 left and right, have retractable pins operated by electrical actuators. Latches 9, 10 and 11 have fixed pins.
 B.  Each latch assembly has a rigid door fitting that mates with the portal fitting on the structure when the door closes. Sixteen latch pins which are driven by the electrical actuators, extend through the portal and door fittings to latch the door in the fully closed position.
 C.  Sixteen actuators are installed on the fuselage structure around the door circumference. Each actuator has an AC motor with integral brake, thermal overload protection, a reduction gear train, and a jackscrew which is integral with the latch pin, and the manual drive input. Limit switches inside the actuator control the extend and retract strokes. Three-phase electrical power is supplied from the right main power center panel P15, main deck cargo handling bus. Manual drive input has a shear pin installed in the manual drive receptacle and held by a removable plate. The pin is designed in such the way that, if the manual crank torque is more than the limit, it will shear to protect the actuator. A groove is machined on the pin to make the removal easier if the pin shears.
　
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