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DUCT LEAK AND OVERHEAT DETECTION -INTRODUCTION

Purpose
The duct leak and overheat detection system (DLODS) monitors the pneumatic ducts and engine anti-ice ducts for leaks.
General
DLODS has an interface with the pneumatic and engine anti-ice systems. Valves in these systems close automatically to stop the leak. A duct leak that does not stop can cause structural damage to the airplane. EICAS messages tell the crew about the duct leak.
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DUCT LEAK AND OVERHEAT DETECTION -INTRODUCTION

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777 AIRCRAFT MAINTENANCE MANUAL

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DUCT LEAK AND OVERHEAT DETECTION -GENERAL DESCRIPTION

General
The duct leak and overheat detection system (DLODS) has these detectors:
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Wheel well fire detectors (ref)

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Fan case overheat detectors

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Strut overheat detectors

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Wing duct leak detectors

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Body duct leak detectors.

Three identical DLODS control cards monitor the detectors:
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Left DLODS control card

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Center DLODS control card

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Right DLODS control card.

Interfaces
The DLODS control cards have these interfaces:
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Pneumatic system (ASCPC)

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Engine anti-ice system (ACIPS cards -EAI)

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Overhead panel ARINC 629 system (OPAS)

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APU controller (APUC)

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Warning electronic system (WES)

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AIMS primary display system and central maintenance computing function.

Wheel Well Fire Detection
If a wheel well fire detector finds a fire, the DLODS control cards send a signal on the data bus. The warning electronic system turns on the fire bell and the master warning lights. The AIMS shows an EICAS warning message.
When you do a fire/overheat test, you test the wheel well fire detection part of DLODS, but not the duct leak and overheat detection part.
See the fire protection section for more information about the fire/overheat test (SECTION 26-00).
See the wheel well fire detection system section for more information about the wheel well fire detection system (SECTION 26-17).
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DUCT LEAK AND OVERHEAT DETECTION -GENERAL DESCRIPTION

Duct Leak and Overheat Detection
If a detector finds an overheat condition, the DLODS control cards send a signal on the data bus. The warning electronic unit turns on the master caution aural. The AIMS turns on the master caution lights and shows an EICAS caution message. For a fan case overheat condition, the DLODS control cards also send a signal to the EAI ACIPS cards to close the engine anti-ice valve. For a strut overheat condition, a wing duct leak, or a body duct leak, the DLODS control cards send a signal to the ASCPC. Pneumatic system valves close automatically to isolate the leak. A signal to the APUC causes the APU surge valve to open if necessary.
BITE
The DLODS cards continuously monitor the detectors for open and short circuits. For either condition, the DLODS control cards send a signal to the AIMS. A status message shows which detector has failed.
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DUCT LEAK AND OVERHEAT DETECTION -GENERAL DESCRIPTION

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DUCT LEAK AND OVERHEAT DETECTION -COMPONENT LOCATIONS

Engine Struts and Nacelles
These DLODS components are in the engine struts and nacelles:
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Right strut overheat detectors

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Right fan case overheat detector

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Left strut overheat detectors

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Left fan case overheat detector.

Wings and Fuselage
These DLODS components are in the wings and fuselage:
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Right wing duct leak detector

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Body duct leak detectors

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Left wing duct leak detector.

Main Equipment Center
These DLODS components are in the main equipment center:
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Left DLODS control card

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Right DLODS control card

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Center DLODS control card.

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DUCT LEAK AND OVERHEAT DETECTION -COMPONENT LOCATIONS
　
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