S 864-012
(5)
Push and hold the ENG test switch on the pilots aft control stand, P8. Make sure these indications occur.
(a)
The L and R ENG OVHT light comes on (on P8).
(b)
The EICAS messages L and R ENG OVHT show on the top display.
S 864-017
S 864-018
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757 MAINTENANCE MANUAL
(c) These EICAS messages show on the bottom display: 1) L STRUT ON DET 1 2) R STRUT OH DET 1 3) L STRUT OH DET 2 4) R STRUT OH DET 2
S 754-013
(6) Release the ENG test switch and make sure the alert indications stop.
E. Put the Airplane Back to Its Usual Condition
S 434-024
(1)
Install the strut pneumatic duct if disconnected (AMM 36-11-01/401).
S 414-014
(2)
Install the strut access panels (AMM 06-43-00/201).
S 444-025
(3)
Do this procedure: Thrust Reverser Activation (AMM 78-31-00/201).
(4)
Remove electrical power if it is not necessary (AMM 24-22-00/201).
S 864-015
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757 MAINTENANCE MANUAL
ENGINE TURBINE COOLING OVERHEAT DETECTION - DESCRIPTION AND OPERATION
_____________________________________________________________________
General
_______
A. Dual-loop overheat detection systems are installed in each engine turbine area. These systems monitor engine turbine cooling air temperatures, and provide alerts for overheat conditions.
B. The systems use power from the 28-volt DC battery bus, with alternate power from the right main dc bus. The circuit breakers for each system are on overhead circuit breaker panel P11 (Fig. 2). The system contains no on/off switches.
C. The overheat detection systems are each composed of a dual-loop detector. Thus, each loop of a fire detection system has one detector switch.
D. Each engine has a fire/overheat logic/test card, and both systems have one fire/overheat test panel.
E. Both systems operate in AND logic. Thus, both loops of a system must
sense overheat condition in order for an alarm to be given.Component Details (Fig. 1)
_________________
A. Overheat Detectors__________________
(1)
The overheat detectors are temperature-sensitive, normally-closed switches. The switches are of bi-metallic construction, and function on the differential expansion properties of the two metals.
(2)
Both switches are mounted on a mixer block, located at the nine o'clock position on the turbine case. The mixer block is fed with turbine cooling air by an air sampling tube. When turbine cooling air temperature exceeds the trip point of the switch, the switch opens to provide an overheat signal.
B. Fire/Overheat Logic/Test Cards______________________________
(1)
Two AFOLTS (Automatic Fire/Overheat Logic/Test System) cards interpret detection switch signals, provide system functional tests, and output fire warning and fault indication signals. Each card handles the overheat detection systems for one engine.
(2)
The AFOLTS cards are located in the P54 card file.
C. Fire/Overheat Test Panel________________________
(1)
The fire/overheat test panel contains a momentary pushbutton switch
-ENG. This switch initiates a test of the engine turbine cooling overheat and strut overheat detection systems. The test results in cockpit fire and overheat indications.
(2)
The test panel also has an amber SYS FAIL - FAIL P-RESET switchlight. This switchlight indicates a fire, overheat, or smoke detection system failure. The switchlight is pressed to reset.
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