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(b) When a detector element pressure switch opens (integrity switch) or closes (alarm switch), the equivalent loop resistance is changed, and the voltage sensed by the control card changes. The card determines which signal is sensed, and sends an appropriate (alarm or fault) signal to the AFOLTS card.
(2)
AIRPLANES WITH GRAVINER FIRE DETECTORS; Refer to the data that follows:
(a)
When temperature increases, the resistance of the fire detector element drops, and the detector card senses the voltage across the capacitance, triggering a fire indication. If the detector is shorted, contaminated or has opened up, only the voltage across the detector resistance changes. The detector card interprets this as a fault, and provides a fault indication.
(b)
When an overheat detector element pressure switch opens (integrity switch) or closes (alarm switch), the loop resistance is changed, and the voltage sensed by the control card changes. The card determines which signal is sensed, and sends an appropriate (alarm or fault) signal to the AFOLTS card.
(3)
The AFOLTS card configures the signals from each system in AND logic, and determines the appropriate output to the flight crew as shown in table 1. Table 1 illustrates the normal operating mode.
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(5)
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~............................................................ | Logic System Operation Engine Fire/Ovht Detection Loops | | Logic AND Configuration | | Table 1 | .............................................................. | INPUTS TO AFOLTS | AFOLTS OUTPUTS | ..............................................................
| | | FIRE | OVERHEAT |
| LOOP 1 | LOOP 2 | DETECTION | DETECTION |
| | | SYSTEMS | SYSTEMS |
.............................................................. | ALARM | ALARM | FIRE | OVHT | .............................................................. | ALARM | - - -| EICAS LOOP 1 | EICAS LOOP 1 | .............................................................. | ALARM | FAULT | FIRE | OVHT | .............................................................. | - - -| ALARM | EICAS LOOP 2 | EICAS LOOP 2 | .............................................................. | FAULT | ALARM | FIRE | OVHT | .............................................................. | FAULT | - - -| EICAS LOOP 1 | EICAS LOOP 1 | .............................................................. | FAULT | FAULT | FIRE | FAIL | .............................................................. | - - -| FAULT | EICAS LOOP 2 | EICAS LOOP 2 | 2...........…..........…..................…..................1Dual Loop Faults.
(a)
Dual loop engine fire detection system faults, which render the system inoperable, will produce FAIL outputs from AFOLTS on completion of a system test. Table 2 illustrates the test mode.
(b)
Dual loop engine fire detection faults, detected during normal operation, will show a fire condition. An engine fire indication will be displayed on the flight deck, along with the appropriate EICAS messages.
An engine fire indication is given by the following:
(a)
The appropriate red (LEFT or RIGHT) fire switch handle, on the P8 control stand, lights up and unlocks.
(b)
The appropriate red (L or R) FUEL CONTROL switch, on quadrant stand P10, lights up.
(c)
The red FIRE light, on captain's instrument panel P1-3, comes on.
(d)
The appropriate fire warning message - L or R ENGINE FIRE, is displayed on EICAS (Engine Indication and Crew Alerting System - P2 panel).
(e)
The red master WARNING lights, on glareshield panels P7, come on.
(f)
The fire bell sounds, on the flight deck aural warning speakers.
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