fire detection system 1808

7/27/2019 Fire Detection System 1808

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O2

FuelHeat

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Class A Class B Class C Class D

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The design of the fire detection system is differentaccording to the area which is monitored.

The purpose:

-Safety of passengers and flight crews-Economical purposes

The Fire Detection System is interconnected withother system as well.

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The design is depends on the area on the a/c

Divide into 2:

1. Overheat and fire detection

2. Smoke detection

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Thermo sensitive loops detect fire and trigger the warning of the Fire Detection Unit (FDU) when thetemperature reaches the threshold of the monitoredarea.

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Two independent loops are installed in each engine.

Connected in parallel

Purpose is to prevent spurious fire warning

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Fire–

excessive overheat / flammable fluid leaks.

Thermo-sensitive elements detect fire / overheatconditions. – trigger the fire warning by Fire Detection

Unit (FDU). ENG/APU FIRE panel (Fig. 1) includes control,

indications and test function for each engine.

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Engine AGENT 1 or 2 switch

Engine 1 or 2 TEST switch

Engine 1 or 2 FIRE switch

FIG. 1

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Function of Panel



(1) ENG 1(2) FIRE pushbutton switch

The ENG 1(2) FIRE pushbutton switch can be pushed

only if the safety guard is open.Each pushbutton switch has three main functions:

indicate the FIRE warning generated by the FireDetection Unit,

activate the microswitches involved in theextinguishing procedure,

arm the discharge function for bottles 1 and 2

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(2) TEST pushbutton switchThe TEST pushbutton switch (one per engine)

checks the condition of the:fire detectors (Loops A and B), Fire Detection Unit(FDU), indications, warnings and associated wirings(loop test),

percussion cartridge filaments of the fire extinguisherbottles and associated wiring (squib test).

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a FIRE warning which comes on red on the ENG 1(2)FIRE pushbutton switch after a positive fire detection

a manual test capability of the system

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2 fire detection loops parallel in fire zones, cnnected toFDU. Each fire detection loop

comprises three detectors connected in parallel,

one FDU per engine, which processes signals from thedetectors,

an ENG/APU FIRE panel on the overhead panel withper engine:

-one ENG FIRE pushbutton switch,-one TEST pushbutton switch,

associated warnings and indications

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FIG. 1

FIG 1 – Fire

Detection Unit

(FDU)13



FIG. 2

A – Engine and

APU fire panel

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FIG 3 - Pylon fire

detector

FIG. 3

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FIG. 4

FIG 4 - Fan fire

detector

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FIG 5 - Core fire

detector

FIG. 5

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Pylonfire

detector

Pylonfire

detector

Core firedetector

Core fire

detector

Fan firedetector

Fan fire

detector

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The engine fire and overheat detection system gets theelectrical power from the DC system of the aircraft.

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(1) Sensing element A sensing element is a tube 0.063 in. (1.6 mm) in outer diameter and 0.018

in. (0.46 mm) in thickness.

It contains a hydrogen-charged titanium core with a spiral wound around it.This spiral is made of an inert material which has a special property: it can giveoff and absorb a gas.

The gap between the sensing-element outer-tube wall and the core is filled

with helium. The initial pressure of the helium is related to the pre-set temperature

threshold selected for each sensing element.

The sensing element reacts according to the ideal gas law.

One end of the sensing element is hermetically soldered and the other one is

connected to a 1 in. (25.4 mm) diameter stainless steel body called responder.

Fire Detector

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(2) Responder assembly The responder contains a chamber connected to two pressure switches :

an ALARM switch and a MONITOR switch. The free end of the responder isconnected to the aircraft electrical circuit.

The detector has two sensing functions. It responds to an overall averagetemperature threshold or to a highly localized discretetemperature caused by impinging flame or hot gases. This results in the ALARM switch closure. theaverage and discrete temperatures cannot be adjusted.

In addition, the averaging and discrete functions are reversible.

When the sensor tube has cooled, the average gas pressure decreases and thecore material absorbs the discrete hydrogen gas.

If the detector leaks, the gas pressure decrease causes the MONITOR switch toopen and generates a detector fault signal.

The system then does not operate during test.21



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fire detection system 1808

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