The document provides information on fire protection systems for the B 737 NG, including engine, APU, cargo compartment, main wheel well, and lavatory fire protection. It describes the detection and extinguishing systems for each area. Engine fire detection uses dual gas pressure detector loops to sense overheat or fire conditions. The engines and APU have fire extinguishing bottles that discharge halon when the fire switch is activated. Cargo compartments have smoke detectors in dual loops and can be select to single loop operation. Main wheel wells and lavatories have smoke or heat detection but no extinguishing systems.
1. B 737 NG Ground School.
See the aircraft study guide at www.theorycentre.com
The information contained here is for training purposes only. It is of a general nature it is
unamended and does not relate to any individual aircraft. The FCOM must be consulted for
up to date information on any particular aircraft.
5. Engine Fire Protection
Engine fire protection consists of these systems:
• engine overheat and fire detection powered by the battery bus
• engine fire extinguishing powered by the hot battery bus.
Engine Overheat and Fire Detection
Each engine contains two overheat/fire detector loops. Each loop provides both
fire and overheat detection. As the temperature of a detector increases to a
predetermined limit, the detector senses an overheat condition. At higher
temperatures, the detector senses a fire condition. Normally, both detector loops
must sense a fire or overheat condition to cause an engine overheat or fire alert.
The ENG OVERHEAT light or engine fire switch remains illuminated until the
temperature drops below the onset temperature.
General Description
Each engine has eight detectors. The detectors monitor four sections of the engine.
In each section, two detectors attach to a support tube and make an assembly. An
assembly has one detector from loop A and one from loop B.
Location
These are the locations of the engine fire detectors:
* Two on the upper fan case section
* Two on the lower fan case section
* Two on the left core section
* Two on the right core section.
6. Loop A Pressure switch
Loop B Pressure switch
TYPICAL FIRE DETECTOR ASSEMBLY
7. TYPICAL FIRE DETECTOR
Sealed gas pressure line
Pressure switch.
Low pressure = Fault
Increased pressure = Overheat
Higher pressure = Fire.
8. The three pressure switches sense these conditions:
Overheat
Fire
Fault (loss of gas pressure).
Gas pressure in the sense tube holds the fault pressure switch in the closed position.
The other two pressure switches close when the gas pressure increases because of
an overheat or fire condition.
The overheat and fire signals go to the engine and the APU fire detection module. This
module supplies overheat or fire indication in the flight compartment.
If the pressure in the sense tube decreases, the fault switch opens. This switch sends
the fault signal to the engine and APU fire detection module.
10. The indications of an engine overheat are:
• both MASTER CAUTION lights illuminate
• the OVHT/DET system annunciator light illuminates
• the related ENG OVERHEAT light illuminates.
Gas filled line sealed
11. The indications of an engine fire are:
• the fire warning bell sounds
• both master FIRE WARN lights illuminate
• the related engine fire switch illuminates
• all related engine overheat alert indications illuminate.
Gas filled line sealed
12. Overheat and Fire detection.
Protect Engine and Pylon (Strut)
Dual loop Gas pressure detectors
APU Single loop gas pressure
detector. Fire detection Only.
13. An OVHT DET switch for each engine, labelled A, B, and NORMAL, permits
selection of either loop A or B, or both A and B, as the active detecting loops.
The system contains a fault monitoring circuit. If one loop fails with the OVHT
DET switch in NORMAL, that loop is automatically deselected and the remaining
loop functions as a single loop detector. There is no flight deck indication of single
loop failure. If both loops fail on an engine, the FAULT light illuminates and the
system is inoperative.
If the OVHT DET switch is positioned to A or B, the system operates as a single
loop system. The non–selected loop is not monitored. If the selected loop fails, the
FAULT light illuminates and the system is inoperative.
14. Engine Fire Extinguishing
The engine fire extinguisher system consists of two engine fire extinguisher
Bottles located in the Left main wheel well, two engine fire switches, two BOTTLE
DISCHARGE lights, and an EXT TEST switch.
Either or both bottles can be discharged into either engine.
APU bottle has one
squib. The green APU
light will illuminate in test
position 1 and 2
15. The engine fire switches are normally locked down to prevent inadvertent
shutdown of an engine. Illumination of an engine fire switch or ENG OVERHEAT
light unlocks the engine fire switch. The switches may also be unlocked manually.
Normal Locked
Fire switch illuminated
Solenoid unlocks.
Or manual unlock
Button located under
the fire switch.
16. Pulling the engine fire switch up:
• closes both the engine fuel shutoff valve and the spar fuel shutoff valve
• closes the engine bleed air valve resulting in loss of wing anti–ice to the
affected wing and closure of bleed air operated pack valve
• trips the generator control relay and breaker
• closes the hydraulic fluid shutoff valve. The engine driven hydraulic
pump LOW PRESSURE light is deactivated
• disables thrust reverser for the related engine.
• allows the engine fire switch to be rotated for discharge
• arms one discharge squib on each engine fire extinguisher bottle.
Rotating the engine fire switch electrically “fires” a squib, discharging the
extinguishing agent into the related engine. Rotating the switch the other way
discharges the remaining bottle.
The L or R BOTTLE DISCHARGE light illuminates a few seconds after the
engine fire switch is rotated, indicating the bottle has discharged.
Turning either number 1 or 2 fire switch clockwise fires the right bottle
squib for that engine.
17. 2 Fire extinguishing bottles for the engines located in the Left main wheel well
18. The engine fire extinguisher bottles are spherical. Each bottle contains halon and
nitrogen at a pressure of 800 psi at a temperature of 21C (70F).
If the bottle temperature increases to 130C, (266F) the safety relief port ruptures.
This releases halon into the wheel well.
The discharge tubing fittings from the two fire extinguisher bottles are different size.
Also the tubing has coloured tape, yellow for engine 1 and blue for engine 2.
When an engine fire extinguisher bottle pressure is less than 250 psi, the bottle
pressure switch closes. The related BOTTLE DISCHARGED amber light on the
overheat/fire protection panel comes on.
20. Each Fire extinguisher bottle has 2 squibs 1 Eng 1 and 1 for Eng 2
HOT BATTERY BUS
BOTTLE DISCHARGE light indicates LOW Pressure
21. APU Fire Protection
APU fire protection consists of these systems:
• APU fire detection powered by the battery bus.
• APU fire extinguishing powered by the hot battery bus.
22. APU fire detection powered from the Battery Bus
BATTERY BUS
Single loop gas pressure
detector. Fire detection Only.
23. APU Fire Detection
A single fire detection loop is installed on the APU. As the temperature of the
detector increases to a predetermined limit, the detector senses a fire condition.
The APU fire switch remains illuminated until the temperature of the detector has
decreased below the onset temperature.
The system contains a fault monitoring circuit. If the loop fails, the APU DET INOP
light illuminates indicating the APU fire detection system is inoperative. In this case
the APU must not be operated as a fire condition would not be detected.
The indications of an APU fire are:
• the fire warning bell sounds
• both master FIRE WARN lights illuminate
• the APU fire switch illuminates
• the APU automatically shuts down
• the wheel well APU fire warning horn sounds, (on the ground only), and the wheel
well APU fire warning light flashes.
24. The two pressure switches sense for these conditions:
* Fire
* Fault (loss of gas pressure).
25. APU GROUND CONTROL PANEL
Located in the Right Main Wheel well
APU Fire
Warning Horn
APU bottle
discharge switch
APU Fire control
Handle
Fire warning horn
cut out switch
APU Fire warning
Light
26. APU Fire Extinguishing
The APU fire extinguisher system consists of one APU fire extinguisher
bottle, an APU fire switch, an APU BOTTLE DISCHARGE light, and an EXT
TEST
switch.
The APU ground control panel located in the right main wheel well also
contains an APU fire warning light, an APU BOTTLE DISCHARGE switch, an
APU fire control handle and APU HORN CUTOUT switch.
The APU fire switch is normally locked down to prevent inadvertent shutdown
of the APU. Illumination of the APU fire switch unlocks the switch. The switch
may also be unlocked manually.
Pulling the APU Fire switch up:
• provides backup for the APU automatic shutdown feature
• deactivates the fuel solenoid and closes the APU fuel shutoff valve
• closes the APU bleed air valve
• closes the APU air inlet door
• trips the APU generator control relay and breaker
• allows the APU fire switch to be rotated for discharge
• arms the APU fire extinguisher bottle squib.
Rotating the APU fire switch in either direction electrically “fires” the squib
discharging the extinguishing agent into the APU. The APU BOTTLE
DISCHARGE light illuminates after a few seconds, indicating the bottle has
discharged (less than 250psi).
27. There is only 1 APU bottle squib. The Fire switch can be turned in either
direction to fire the squib.
29. Main Wheel Well Fire Protection
Main wheel well fire protection consists of fire detection powered by the No. 2 AC
transfer bus.
Note: The main wheel well has no fire extinguishing system. The nose wheel
well does not have a fire detection system.
Main Wheel Well Fire Detection
A single fire detector loop is installed in the main wheel well. As the temperature
of the detector increases to a predetermined limit, the detector senses a fire
condition. The WHEEL WELL fire warning light remains illuminated until the
temperature of the detector has decreased below the onset temperature.
The indications for a main wheel well fire are:
• the fire warning bell sounds
• both master FIRE WARN lights illuminate
• the WHEEL WELL fire warning light illuminates.
30. The sensing element is a thermistor type with resistance inversely proportional to
temperature. As the element temperature increases, the resistance decreases. If
any portion of the sensing element is above alarm temperature of 205C (400F), the
element resistance decreases sharply. The single wire in the centre of the core is
the power lead and the outside tube is electrically grounded. The insulating
resistance of the core material decreases suddenly at the alarm temperature.
Current flows through the core material to ground when alarm temperature is
sensed.
The sensing element has a
single strand of nickel wire
embedded in insulation. The
insulation is impregnated with a
salt compound and is in a tube.
Outer case
Ground
Insulating Material
Nickel wire +
34. Cargo Compartment Fire Protection
Cargo fire protection consists of these systems:
• cargo compartment smoke detection powered by DC bus 1 and DC bus 2
• cargo compartment fire extinguishing powered by the hot battery bus.
Cargo Compartment Smoke Detection
The forward and aft cargo compartments each have smoke detectors in a dual
loop configuration. Normally, both detection loops must sense smoke to cause an
alert.
In the event of a detector failure, the system can be manually converted to
single-loop detection through the DETECT SELECT switch on the cargo fire
control panel. In the event of a power failure in one loop the system automatically
converts to single-loop detection.
Cargo Compartment Fire Warning
The indications of a cargo compartment fire are:
• the fire warning bell sounds
• both master FIRE WARN lights illuminate
• the FWD/AFT cargo fire warning light(s) illuminates.
45. Cargo Compartment Smoke and Heat Detectors
Detects Particles present in the air.
Or air temperature over 110 C
Normally requires 1
detector in loop A and 1
In group B to detect a
Fire.
Can be configured
Automatically or Manually
for Single Loop operation.
46. Cargo Compartment Fire Extinguishing
One or two fire extinguisher bottles are installed in the air conditioning mix bay on
the forward wing spar. Detection of a fire in either the forward or aft compartment will
cause the FWD or AFT cargo fire warning light to illuminate. The extinguishers
are armed by pushing the appropriate cargo fire ARMED switch. Once armed, the
first bottle is discharged by pushing the cargo fire DISCH switch. This results in
the total discharge of the first bottle contents into the selected compartment. The
second bottle discharge is metered to discharge at a reduced flow into the selected
compartment. Discharge of the second bottle may be disabled if the system is
disarmed. The cargo fire DISCH light illuminates when a bottle is discharged. It
may take up to 30 seconds for the light to illuminate. On landing, if the first bottle
was discharged and the system remains armed, the second bottle discharge is
inhibited.
47. Halon 1301 Fire extinguishing Agent
Pressurised with Nitrogen.
1 Bottle gives a fire suppression
time of 60 minutes.
Located in Air conditioning distribution bay.
Behind the Aft wall of FWD cargo compartment
48. Bottle 2 is on a 60 minute timer.
Discharge is controlled through a metering valve
Operates if still in Air mode.
Inhibited in Ground mode.
Bottle 1 suppresses Fire for 60 minutes.
2 bottles offer a total of 180
minutes of Fire suppression.
2 Bottle installation
50. Lavatory Fire Protection
Lavatory fire protection consists of these systems:
• lavatory smoke detection
• lavatory fire extinguishing (heat activated).
This is aircraft dependent with variations!
The lavatory smoke detection system monitors for the presence of
smoke. When smoke is detected:
• an aural warning sounds
• the red alarm indicator light on the lavatory smoke detector panel
illuminates and the appropriate amber lavatory call light will flash
• the amber lavatory SMOKE light on the forward overhead panel
illuminates.
Amber Lavatory call light
51. Some aircraft have a lavatory smoke light on the FWD overhead panel.
SMOKE DETECTOR
52. Lavatory Fire Extinguisher System
A fire extinguisher system is located beneath the sink area in each lavatory.
When a fire is detected:
• fire extinguisher operation is automatic
• flight deck has no indication of extinguisher discharge.
The extinguisher bottle has two discharge ports. The ports have eutectic
plugs. These plugs melt at high temperatures. When there is an overheat or
fire condition, this occurs:
* Temperature indicators change colour (white to black)
* Eutectic plug melts
* Extinguisher releases halon to stop the fire.
Eutectic Definition
Mixture of two or more components in such proportion that their combined melting
point is the lowest attainable in some cases as low as 60 C (140 F).
Eutectic alloys are fusible: upon cooling they convert from liquids to intimately mixed
solids.
Solder that is made of 63% tin and 37% lead. Eutectic solder is also known as 63/37
solder will go directly from a solid to liquid state when melted.
53. Lavatory Fire Extinguisher
Heat Sensitive discharge nozzle which discharges agent into waste bin
Heat Activated Nozzles
Both nozzles discharge toward the towel disposal container.
Flat black – normal condition.
Aluminum – indicates extinguisher has discharged.
55. The indication that a lavatory fire extinguisher has been discharged is;
a) The heat activated nozzle will be black.
b) The bottle exterior surface will be an aluminium colour.
c) The heat activated nozzle will be an aluminium colour.
d) The bottle pressure gage will indicate zero pressure.
56. The indication that a lavatory fire extinguisher has been discharged is;
a) The heat activated nozzle will be black.
b) The bottle exterior surface will be an aluminium colour.
c) The heat activated nozzle will be an aluminium colour.
d) The bottle pressure gage will indicate zero pressure.
Heat Activated Nozzles
Both nozzles discharge toward the towel disposal container.
Flat black – normal condition.
Aluminum – indicates extinguisher has discharged.
57. The power source for fire extinguishing is;
a) Transfer bus No 1.
b) The switched hot battery bus.
c) The hot battery bus.
d) Transfer bus No 2.
58. The power source for fire extinguishing is;
a) Transfer bus No 1.
b) The switched hot battery bus.
c) The hot battery bus.
d) Transfer bus No 2.
Engine Fire Protection
Engine fire protection consists of these systems:
• engine overheat and fire detection powered by the battery bus
• engine fire extinguishing powered by the hot battery bus.
60. Pulling the engine fire switch up cause what 8 things to happen?
1.
ARMS 1 EXTINGUISHER SQUIB ON EACH BOTTLE.
2.
CLOSES BOTH THE SPAR AND ENGINE FUEL VALVES.
3.
CLOSES THE HYDRAULIC PUMP SHUTOFF VALVE.
4.
CLOSES THE ENGINE BLEED AIR VALVE.
5.
DISABLES THE THRUST REVERSER.
6.
TRIPS THE GENERATOR CONTROL BREAKER.
7.
INHIBITS THE EDP HYDRAULIC LOW PRESSURE LIGHT.
8.
ALLOWS THE SWITCH TO ROTATE TO FIRE THE SQUIB.
61. How many fire extinguisher bottles are there for the engines?
62. How many fire extinguisher bottles are there for the engines?
63. Fire Protection.
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