(12)
 Normal operation of the uplock hook is by hydraulic fluid directed to the uplock actuator. This latches and unlatches the hook in the proper sequence as governed by the door-operated sequence valve. Provision is made to release the uplock in the absence of hydraulic pressure by means of an electrical actuator attached to the release cam. This cam contacts a follower which releases the hook. At the same time a door opening cam and follower mechanism operates the cable system which unlocks the door actuator and allows the doors to open.

 (13)
 When the gear is selected DN, hydraulic pressure causes the door actuating cylinder to unlock and retract. This opens the doors. The internal lock in the actuator may be mechanically unlocked by means of a rotating shaft on the cylinder end of the actuator. Rotation of this shaft unlocks the internal lock mechanism when the alternate landing gear release system is operated or when the ground door release handle is operated. Simultaneously, the door safety valve releases pressure to return. The doors are then free to fall by gravity.

 B.
Control

 (1)  
Extension and retraction of the landing gear is controlled by moving the landing gear control handle to the UP, OFF, and DN position.

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 ALL  ú ú 04 Page 18 ú Jun 10/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
FAULT ISOLATION/MAINT MANUAL

BODY GEAR AND DOOR EXTENSION AND RETRACTION
COMPONENT  FIG. 102 SHT  QTY  ACCESS/AREA  REFERENCE 
ACTUATOR - DOOR  2  2  L, R BODY GEAR WHEEL WELL  32-33-27 
ACTUATOR - DOWNLOCK  1  2  L, R BODY GEAR  32-33-15 
ACTUATOR - GEAR  1  2  L, R BODY GEAR  32-33-01 
ACTUATOR - UPLOCK  2  2  L, R BODY GEAR WHEEL WELL, UPLOCK MECHANISM  32-33-14 
BEAM - DOOR ACTUATOR  3  2  ACTUATOR L, R BODY GEAR WHEEL WELL, DOOR  32-33-28 
BUNGEE - DOWNLOCK  1  2  L, R BODY GEAR  32-33-16 
JOINT - DOOR ACTUATOR SWIVEL  3  2  L, R BODY GEAR WHEEL WELL, DOOR ACTUATOR  32-33-26 
MECHANISM - DOOR OPERATED SEQUENCE VALVE  3  2  L, R BODY GEAR WHEEL WELL  32-33-02 
MECHANISM - DOWNLOCK OPERATED SEQUENCE VALVE  1  2  L, R BODY GEAR WHEEL WELL  32-33-04 
MECHANISM - UPLOCK  1  2  L, R BODY GEAR WHEEL WELL  32-33-08 
MECHANISM - UPLOCK OPERATED SEQUENCE VALVE  2  2  L, R BODY GEAR WHEEL WELL, UPLOCK MECHANISM  32-33-07 
VALVE - DOOR OPERATED SEQUENCE  3  2  L, R BODY GEAR WHEEL WELL  32-33-02 
VALVE - DOOR SAFETY  3  2  L, R BODY GEAR WHEEL WELL  32-33-29 
VALVE - DOWNLOCK OPERATED SEQUENCE  1  2  L, R BODY GEAR WHEEL WELL  32-33-04 
VALVE - UPLOCK OPERATED SEQUENCE  2  2  L, R BODY GEAR WHEEL WELL, UPLOCK MECHANISM  32-33-06

 * SEE WM EQUIPMENT LIST
Body Gear and Door Extension and Retraction - Component Index
Figure 101

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 ú  01  Page 101
 ú  Oct 10/88 

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

747-400 FAULT ISOLATION/MAINT MANUAL 
SEQUENCE VALVE AND MECHANISM DOWNLOCK OPERATED 
SEE  B 
UPLOCK MECHANISM 
SEE  C  D  SHT 2 
LANDING GEAR L OR R BODY ASEE  BUNGEE DOWNLOCK  ACTUATOR GEAR 
JURY STRUT (REF) 

OUTER 
CYLINDER 
(REF) 
DRAG STRUT 
(REF)  DOWNLOCK 
ACTUATOR  FWD 
DOWNLOCK OPERATED SEQUENCE VALVE  DOWNLOCK OPERATED  L OR R BODY LANDING GEAR 
MECHANISM  SEQUENCE VALVE  A 

UPPER BODY GEAR JURY STRUT (REF)
KEEL BEAM
(REF)

DOWNLOCK OPERATED SEQUENCE VALVE AND MECHANISM B
Body Gear and Door Extension and Retraction - Component Location Figure 102 (Sheet 1)
　
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