26-17-01
 ALL  ú ú 01 Page 404 ú May 28/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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757 MAINTENANCE MANUAL
 WING AND BODY DUCT LEAK DETECTION - DESCRIPTION AND OPERATION
_____________________________________________________________
 1.  General_______
 A.  The wing and body duct leak detection system monitors the temperature along the left and right wing bleed air duct zones, the air conditioning bays and the APU duct zone. When an overheat condition is detected in any of these zones, a caution alert is provided in the flight compartment.
 B.  The system is divided into left and right zones, each containing dual detection elements set to trigger an alarm at 255°F. The left zone has five elements wired in series and extend, along the left wing leading edge, the left air conditioning bay, the wheel well, the aft cargo compartment, and the pressure bulkhead aft to the APU. The right zone has two elements wired in series and extend along the right wing leading edge, and the right air conditioning bay.
 C.  The two zones are wired to the duct leak and wheel well fire control card in P50 electrical systems card file. If an overheat is sensed, the appropriate duct leak caution light on pneumatic control panel (P5) lights, and a level B caution appears on EICAS. A system test switch is provided on the miscellaneous test panel on P61 sidewall panel. The switch is labeled "DUCT LEAK". A successful test, lights the two duct leak lights on pnuematic control panel (P5). BITE is provided on the control card at P50 to assist with trouble shooting, and a DUCT LEAK BITE message displays on the EICAS maintenance page if a fault exists.
 D.  The wing and body duct leak overheat detection system uses 115 Vac, and 28 Vdc power.
 2.  Component Details (Fig. 1)_________________
 A.  Duct Leak Detectors
___________________
 (1)  Detector elements consist of a fine nickel wire surrounded by a heat sensitive insulation, enclosed in a steel tube. Electrical connectors are attached to each end. The resistance of the heat sensitive insulation decreases as the temperature of the material increases. At a preselected temperature (resistance value), the detector provides an alarm signal (ground) to the detector card in the P50 card file. When the temperature of material cools sufficiently, the alarm signal is automatically cancelled.
 B.  Duct Leak and Wheel Well Fire Circuit Cards
___________________________________________
 (1)  A power supply card, and control card located in P50 serve the functions of the duct leak detection system. These same cards, also serve the functions of the wheel well fire detection system (Ref 26-17-00).
 (a)  The power supply card receives 28 Vdc from the R bus and provides regulated 5 Vdc, 19 Vdc, and 20 Vdc to the control card.
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 26-18-00
 ALL  ú ú 02 Page 1 ú Mar 15/87
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL

Duct Leak Detection - Component Location
Figure 1 (Sheet 1)

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 26-18-00
 ALL  ú ú 01 Page 2 ú Mar 20/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL

DUCT LEAK AND WHEELWELL
P50 CARD FILE FIRE CONTROL CARD (P50)

F
G
Duct Leak Detection Component Location
Figure 1 (Sheet 2)

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 26-18-00
 ALL  ú
 ú  01  Page 3
 ú  Dec 20/88 

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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757 MAINTENANCE MANUAL
 (b)  The control card consists of a microprocessor board, relay board, and display board. It performs monitor and control functions of the system. 1) The microprocessor board contains a microprocessor and
　
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