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______________________________________________ DESCRIPTION AND OPERATION
_________________________
General (Fig. 1)
_______
 A.  The leading edge flap position indicating system provides visual indication on the flight deck of leading edge flap position when flaps are in non-normal configurations. During normal flap operation, there is no separate indication of the position of the leading edge flaps.
 B.  Components used by the leading edge flap position indicating system are the limit switch assemblies in the 8 leading edge flap power drive units, the 3 flap control units, and the EIU's and EICAS display. The system is energized when the flap control units and the EICAS are powered.
Sensitive Annunciator Feedback (Limit) Switch Assembly
______________________________________________________
 A.  There is a switch assembly in each of the 8 leading edge flap power drive units (PDU). The assembly contains two limit switches. One limit switch closes to ground when the PDU is in the flap retracted position, and the other limit switch closes to ground when the PDU is in the flap extended position. When the leading edge flaps are in transit, both limit switches are open.
Flap Control Unit
_________________
 A.  The 3 flap control units process position sensing signals for all flaps in addition to providing flap control and protection. The flap control units receive discrete signals from the limit switches in the LE flap PDU's. The flap control units convert the signals to a serial digital format for transmission to the EIU's on an ARINC 429 bus. The left flap control unit is located on the E1-2 electronics shelf and the center and right flap control units are located on the E2-2 electronics shelf in the main electrical equipment center.
Operation (Figs. 2 and 3)
_________
 A.  Functional Description
 (1)  
When the leading edge flaps are retracted, the extend limit switch in each PDU is open and the retract limit switch is closed, which grounds the "retract" line to the flap control unit. When the LE flaps are in transit, both the retract and the extend limit switches open. When the LE flaps are fully extended, the retract limit switch is open and the extend limit switch closes, grounding the "extend" line to the flap control units.

 (2)  
The FLAPS display appears on the main EICAS whenever flaps are not fully retracted and disappears 15 seconds after flaps are retracted. The normal FLAPS display appears for normal flap configurations and does not show LE flap position. LE flap position is shown in either of two multiple flap displays which appear for non-normal flap configurations.

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

747-400
MAINTENANCE MANUAL

LEADING EDGE FLAP POSITION INFORMATION ON AUXILIARY EICAS DISPLAY
FLAP CONTROL UNITS
MAIN EQUIPMENT CENTER  FLIGHT COMPARTMENT
SEE A
LEFT WING (TOP VIEW)
UNIT DRIVE POWER  CONNECTOR ELECTRICAL 
SEE  B 

SENSITIVE ANNUNCIATOR
A  FEEDBACK SWITCH
ALTERNATE
ASSEMBLY CONTROLLER
B
____LEFT WING LE FLAP INDICATING SYSTEM IS SHOWN.
NOTE: RIGHT WING LE FLAP INDICATING SYSTEM IS EQUIVALENT.
Leading Edge Flap Position Indicating System - Component Location
Figure 1

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 ALL  ú ú 01 Page 2 ú Feb 15/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

F

5
L A P S
NORMAL FLAPS
(LEADING EDGE FLAPS NOT
DISPLAYED FOR NORMAL FLAPS)

 

F
L

5
A P S
MULTIPLE FLAPS-PRIMARY

MULTIPLE FLAPS-ALTERNATE

LE FLAPS
RET RET

INT  RET

EXT  RET
RET  RET
Leading Edge Flap Position Indicating System EICAS Displays
Figure 2

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