S76 Maintenance Training Manual CHC Training Centre (Global)

FIRE PROTECTION
 TABLE OF CONTENTS
GENERAL (S-76A/A+/C) .................................................................................5
ENGINE FIRE DETECTION SYSTEM .........................................................5
SMOKE DETECTION SYSTEM ....................................................................14
ENGINE FIRE EXTINGUISHING SYSTEM (S-76A) ...................................21
ENGINE FIRE EXTINGUISHING SYSTEM (S-76A+/C).............................22

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 GENERAL (S-76A/A+/C)
Fire protection includes a fire detection and indicating system, an electrically
controlled fixed fire extinguishing system for each engine, and a smoke detector
for the baggage compartment. The engine fire detection system uses photocell-type
flame detectors that sense either infrared radiation, such as a flame, or CO2 spikes
of hydrocarbon fire, and cause the proper warning lights to go on. An audible
warning signal notifies the crew of a fire.
Two similar, but independently controlled fire extinguishing systems are installed
to control fires within the engine compartments. If a fire occurs, the NO. I or NO.
2 ENG EMER OFF T-handle on the engine control quadrant is pulled aft, arming
the FIRE EXT switch. Placing the switch to MAIN will cause one container to
discharge its contents into the selected engine compartment.
Placing the switch to RESERVE will discharge the contents of the opposite
container into the same engine compartment if it has not been previously
discharged. Electrical power for the fire extinguishing system is supplied by the
NO. 1 and NO. 2 DC PRI and DC ESNTL buses at 28 VDC through the FIRE
EXT circuit breakers on the upper and lower circuit-breaker panel.
Electrical power for the engine fire detector system is supplied by the DC ESNTL
bus at 28 VDC through the FIRE DETECTOR NO. 1, NO. 2, and TEST circuit
breakers on the lower circuit-breaker panel.
Electrical power for the baggage compartment smoke detector is supplied by the
NO. 1 DC PRI bus at 28 VDC through the SMK DET circuit breaker on the
upper circuit-breaker panel.
The smoke detector test circuit is connected in parallel to the engine fire detector
system for electrical power. Portable fire extinguishers are conveniently mounted on
the right side of the flight controls enclosure and under the forward left passenger
seat.
ENGINE FIRE DETECTION SYSTEM
GENERAL
The engine fire detection system consists of a forward and aft photocell-type flame
detector in each engine compartment, separate control amplifiers, a test switch,
warning lights, and an audible warning system.

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 COMPONENTS
FLAME DETECTORS
Photocell-type flame detectors, sensitive to either infrared radiation or CO2 spikes,
are mounted on the forward and aft firewalls of each engine compartment. Each
detector is installed in such a manner that the optical portion views the fire zone.
FIRE DETECTOR CONTROL AMPLIFIERS
Two fire detector control amplifiers, one for each engine, are located on the pallet.
When a fire occurs, the detector sends an electrical signal to the control amplifier,
which in turn, sends a signal to the warning lights and to the audible warning
system.
FIRE DETECTOR WARNING LIGHTS
Warning lights located inside the NO. 1 and NO. 2 EMER OFF T-handles on the
engine control quadrant and the #1/#2 ENG FIRE PRESS TONE OFF lights on
the pilot’s and copilot’s master warning panel come on during a fire or when the
circuit is checked by operating the FIRE DET TEST switch.
FIRE DETECTOR TEST SWITCH
The FIRE TEST DET switch located on the overhead control panel has three
positions: NORM, AFT/BAG, FWD. When the switch is momentarily positioned
to AFT/BAG, the circuit continuity of the No. 1 and No. 2 engine aft flame
detectors, the baggage compartment smoke detector, and their respective control
amplifier operation is checked by proper warning light indication. If the switch is
positioned to FWD, the circuit continuity of the No. I and No. 2 engine forward
flame detectors and control amplifier operation is checked by proper warning light
indications.
FIRE DETECTOR TEST RELAYS
The No. 1 fire detector test relay K1/1R is mounted on the No. 1 relay panel and
the No. 2 fire detector test relay K1/2R is mounted on the No. 2 relay panel. When
testing the forward flame detectors, electrical power is supplied to the coil of the
No. I relay K1/1 R. With the contacts closed, the NO. 1 ENG EMER OFF and
NO. 2 ENG EMER OFF warning lights in the engine control quadrant T-handle
and also the #1/#2 ENG FIRE PRESS TONE OFF lights in the master warning
panel are illuminated. Testing the aft flame detector is accomplished in the same
manner, only the No. 2 relay K1/2R is energized.

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 SMOKE DETECTION SYSTEM
GENERAL
The smoke detector contains a photocell within a perforated cage. When smoke
enters through the perforated cage, light from a constant source is reflected onto
the photocell causing an output voltage to the control amplifier illuminating the
SMOKE DET BAGGAGE light capsule.
COMPONENTS
SMOKE DETECTORS
The smoke detector is comprised of a labyrinth assembly, containing a constant
light source, a photocell, a test light, and associated circuitry. Air enters the
labyrinth assembly where it is sampled for presence of smoke.
CONTROL AMPLIFIER
The smoke detector control amplifier is located on a pallet on the left side of the
electrical compartment. It is identical to the flame detector amplifier.
TEST SWITCH
When the FIRE TEST DET switch, on the overhead control panel, is positioned
to AFT/BAG, the test light provides a light source detected at the photocell causing
a simulated alarm condition, thus verifying the operation of the smoke detector
and other components of the smoke detector system.

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 ENGINE FIRE EXTINGUISHING SYSTEM (S-76A)
GENERAL
The fire extinguishing system consists of two pressurized bottles of extinguishing
agent which may be discharged one at a time into each engine compartment, or
both may be discharged into either engine compartment.
COMPONENTS
FIRE EXTINGUISHING CONTAINERS (BOTTLES)
The engine fire extinguisher containers are installed aft of the engine compartment
and within the engine aft cowl fairing. Each container is charged to 600 psig
with 1.75 pounds of monobromotrifluoromethane (CF3Br) extinguishing agent
and pressurized with dry nitrogen (N2) at 21’ C (70° F). The container is fitted
with valves and cartridges which are connected to the system. Upon operation,
either cartridge is activated allowing the charge in the container to escape through
the valve. The recharge and safety fitting contains a burst, safety disc to release
the extinguishing agent if the internal pressure becomes excessive due to high
temperature.
DISCHARGE INDICATOR
A discharge indicator, located on the left side of the fuselage, is connected to both
containers and provides a visual indication if either container has discharged due to
excessive pressure.
CONTROLS
GENERAL
The fire extinguisher controls consist of a FIRE EXT switch, an EXT FIRE test
switch on the overhead control panel, and two T-handies on the engine control
quadrant.
FIRE EXTINGUISHING SWITCH
The FIRE EXT switch has three positions: OFF, MAIN, and RESERVE. When
the switch is positioned to MAIN and has been armed by a pulled T-handle, the
extinguishing agent from the container is discharged in the engine compartment
selected by the T-handle. If necessary the switch may be moved to RESERVE to
discharge the opposite container.
FIRE EXTINGUISHING TEST SWITCH
The EXT FIRE test switch has three positions: NORM, OPEN, and SHORT.
During a test, an open or short circuit can be detected within the extinguishing
circuit.

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 ENGINE EMERGENCY OFF T -HANDLES
Two T-handles, labeled “NO. 1 ENG EMER OFF” and “NO. 2 ENG EMER
OFF” are located on the engine control quadrant in the cockpit. During a fire,
warning lights in the respective T-handle will illuminate. When the T-handle is
pulled it will arm the circuit for the affected engine.
ENGINE FIRE EXTINGUISHING SYSTEM (S-76A+/C)
GENERAL
The fire extinguishing system consists of two pressurized bottles of extinguishing
agent which may be discharged one at a time into each engine compartment, or
both may be discharged into either engine compartment.
COMPONENTS
FIRE EXTINGUISHING CONTAINERS
The engine fire extinguisher containers are installed inside the tail cone at station
300. Each container is charged to 600 psig with 1.75 pounds of monobromotr
ifluoromethane (CF3Br) extinguishing agent and pressurized with dry nitrogen
(N2) at 21° C (70° F). The container is fitted with valves and cartridges which are
connected to the system. Upon operation, either cartridge is activated allowing the
charge in the container to escape through the valve. The recharge and safety fitting
contains a burst safety disc to release the extinguishing agent if the internal pressure
becomes excessive due to high temperature.
DISCHARGE INDICATOR
A discharge indicator, located on the left side of the fuselage, is connected to both
containers and provides a visual indication if either container has discharged due to
excessive pressure.
CONTROLS
GENERAL
The fire extinguisher controls consist of a FIRE EXT switch, an EXT FIRE test
switch on the overhead control panel, and two T-handles on the engine control
quadrant.
FIRE EXTINGUISHING SWITCH
The FIRE EXT switch has three positions: OFF, MAIN, and RESERVE. When
the switch is positioned to MAIN and has been armed by a pulled T-handle, the
extinguishing agent from the container is discharged in the engine compartment
selected by the T-handle. If necessary the switch may be moved to RESERVE to
discharge the opposite container.

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 FIRE EXTINGUISHING TEST SWITCH
The EXT FIRE test switch has three positions: NORM, OPEN, and SHORT.
During a test, an open or short circuit can be detected within the extinguishing
circuit.
Engine Emergency Off T -Handles
Two T-handles, labeled “NO. 1 ENG EMER OFF” and “NO. 2 ENG EMER
OFF,” are located on the engine control quadrant in the cockpit. During a fire,
warning lights in the respective T-handle will illuminate. When the T-handle is
pulled, it will arm the circuit for the affected engine.

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 NOTES:

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 QUIZ
FIRE PROTECTION
Each of the statements below is either true or false. Indicate, in the space provided
whether you agree or disagree with the statement.
TRUE or FALSE
1. A fire bottle thermal discharge is indicated by the blowing of a red seal
2. of which there are two, one for each fire bottle.
3. A fire extinguishing system comprises a main and reserve bottle for each
engine
4. located externally to the engine compartment.
5. The bottles are pressurised with dry nitrogen
6. and contain 1.75 lbs of FREON extinguishing agent.
7. Within the discharge valve of each extinguisher is an explosive cartridge
8. which is ignited by 28v d.c. upon retarding the EMERG. OFF T - handle
9. which is located on the engine control quadrant.
10. The FIRE EXT RESERVE/MAIN switch determines whether the main or
reserve bottle is discharged into an engine.
11. The fire bottles can be discharged simultaneously into both engines.
12. If the fire is not extinguished at the first attempt, the reserve bottle may be
utilised
13. after which operation no extinguishing capability will exist for the engine
compartments.
14. The ENG. EMERG OFF LEVER must be moved at least one inch in
order to permit discharging of the extinguishing agent.
15. Fire in the engine compartments and the baggage compartment causes the
fire warnings to operate
16. flame detectors being used in the engine compartments
17. and smoke detectors being used in the baggage compartment
18. both detectors causing a continuous tone warning to be heard.
19. Correct functioning of the flame detectors can be ascertained by operating
the appropriate test switches

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 20. the AFT detector and baggage detector circuits being checked
simultaneously.
21. Smoke, by preventing light reaching a photo-electric cell, causes the
baggage detector to operate.
22. The baggage compartment fire extinguisher is automatically operated by
the detector.
23. An overhead test panel can be used to check the serviceability of the
extinguisher circuits.
24. During the tests the T-handles must not be moved, since this will cause the
extinguisher to operate.
25. Testing for an open circuit causes both the green and red test lamps to
illuminate if test is good.
26. by allowing 55 milliamps current to flow through the cartridges.

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