S 737-017

 (15)
 Do the operational test and the airflow test for the applicable Cargo Smoke Detection System (AMM 26-16-00/501).

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747-400 MAINTENANCE MANUAL
 EQUIPMENT COOLING SMOKE DETECTION SYSTEM - DESCRIPTION AND OPERATION
____________________________________________________________________
General
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 A.  Smoke in the equipment cooling system is sensed by a smoke detector installed between the supply air duct and exhaust air duct.
 B.  The pressure differential between the ducts causes a continuous flow of air through the detector for sampling.
 C.  The smoke detector receives power from 28-volts dc bus No.2. The circuit
 breaker is located P6 overhead circuit breaker panel.Smoke Detector (Fig. 1)
______________
 A.  The smoke detector senses smoke condition in electrical/electronics compartment.
 B.  The detector consists of a photocell and pilot light (LEDs on some detectors) in a light-proof chamber plus associated amplifier, output, and test circuits on a printed circuit card. The detector has inlet and outlet tubes to provide air and smoke.
 C.  Smoke entering the light-proof chamber reflects the light from the pilot lamp (LEDs on some detectors) onto a photocell. Then the photocell causes an increase in output voltage and a signal is relayed to the flight deck. The generated signal creates an EICAS messages.
 D.  The smoke detector is located in left wall of forward lower cargo compartment at STA 581. The smoke detector can be accessed by removing the left wall lining panel in forward lower cargo compartment.
 E.  The smoke detector is a part of equipment cooling system. Refer to 21-58-00/501, Operational Test, for checking the operation of the smoke detector.
Operation
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 A.  Due to the pressure differential between supply air duct and exhaust air duct, the air flow condition is created in smoke detector.
 B.  Electrical power is continuously supplied, and if smoke condition is established by the smoke detector, a discrete signal is sent to EIU and EICAS message is created.
 C.  The system integrity can be checked by CMC ground test for Chapter 21 equipment cooling system (Ref 21-58-00/501).
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747-400
MAINTENANCE MANUAL

BOLT (2) (TYP)
CLAMP (2)
SMOKE DETECTOR
SEE A
ELECTRICAL CONNECTOR
TUBING
SMOKE DETECTOR
A
PILOT LAMP 
OR LED  REFLECTED 
LIGHT  PHOTO CELL 

ELECTRONIC CIRCUIT AND RELAY
AIR IN  AIR OUT
SMOKE PARTICLES
TEST LED LIGHT BEAM LIGHT TRAP(ON SOME(ON SOMEAIRPLANES) AIRPLANES)
SMOKE DETECTOR SCHEMATIC
Equipment Cooling Smoke Detection System Component Location Figure 1
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747-400
MAINTENANCE MANUAL

SMOKE DETECTOR
Equipment Cooling Smoke Detection System Simplified Schematic
Figure 2 (Sheet 1)

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