b737-300/400 fire protection

of 57PT. METRO BATAVIAPT. METRO BATAVIADirectorate of OperationalDirectorate of Operational

737-300/400737-300/400FIRE PROTECTIONFIRE PROTECTION

NextNextMain MenuMain Menu QuitQuit


Control StandControl Stand

Overheat/Fire Protection Panel Overheat/Fire Protection Panel


Overheat/Fire Protection PanelOverheat/Fire Protection Panel- Switches -- Switches -

Engine Fire Warning Switches:Engine Fire Warning Switches:Illuminated –Illuminated –• Indicates a fire condition exists in the respective engine.Indicates a fire condition exists in the respective engine.• Automatically unlocks engine fire warning switch.Automatically unlocks engine fire warning switch.• FIRE WARN lights illuminate.FIRE WARN lights illuminate.• Fire warning bell sounds.Fire warning bell sounds.

Note: The engine fire warning switches also illuminate during an OVHT/FIRE test.Note: The engine fire warning switches also illuminate during an OVHT/FIRE test.



Engine Fire Warning Switches:Engine Fire Warning Switches:The engine fire warning switches are mechanically locked “down” when no fire signal exists.The engine fire warning switches are mechanically locked “down” when no fire signal exists.

The following is a list of items that occur when an engine fire warning switch is “pulled-up”: The following is a list of items that occur when an engine fire warning switch is “pulled-up”: • Allows the engine fire warning switch to be rotated.Allows the engine fire warning switch to be rotated.• Arms one discharge squib on each engine fire extinguisher bottle.Arms one discharge squib on each engine fire extinguisher bottle.• Closes respective engine fuel shutoff valve, hydraulic shutoff valve, and engine bleed air valve.Closes respective engine fuel shutoff valve, hydraulic shutoff valve, and engine bleed air valve.• Trips the respective generator control relay and circuit breaker.Trips the respective generator control relay and circuit breaker.• Thrust reverser isolation valve closes, thereby disabling the thrust reverser.Thrust reverser isolation valve closes, thereby disabling the thrust reverser.• Deactivates the respective engine driven pump hydraulic LOW PRESSURE light.Deactivates the respective engine driven pump hydraulic LOW PRESSURE light.

Rotating the engine fire warning switch left or right will discharge the related engine fire bottle Rotating the engine fire warning switch left or right will discharge the related engine fire bottle extinguishing agent into an area above the center of the respective engine (1 or 2). extinguishing agent into an area above the center of the respective engine (1 or 2).



APU Fire Warning Switch:APU Fire Warning Switch:Illuminated –Illuminated –• Indicates a fire condition exists in the APU.Indicates a fire condition exists in the APU.• Automatically unlocks APU fire warning switch.Automatically unlocks APU fire warning switch.• FIRE WARN lights illuminate.FIRE WARN lights illuminate.• Fire warning bell sounds.Fire warning bell sounds.• APU fire warning horn in main gear wheel well sounds (if aircraft is on the ground).APU fire warning horn in main gear wheel well sounds (if aircraft is on the ground).• APU fire warning light flashes (located on APU ground control panel in main gear wheel well).APU fire warning light flashes (located on APU ground control panel in main gear wheel well).

Note: The APU fire warning switch also illuminates during an OVHT/FIRE test.Note: The APU fire warning switch also illuminates during an OVHT/FIRE test.



APU Fire Warning Switch:APU Fire Warning Switch:The APU fire warning switch is mechanically locked “down” when no fire signal exists.The APU fire warning switch is mechanically locked “down” when no fire signal exists.

The following is a list of items that occur when the APU fire warning switch is “pulled-up”: The following is a list of items that occur when the APU fire warning switch is “pulled-up”: • Allows the APU fire warning switch to be rotated.Allows the APU fire warning switch to be rotated.• Arms the discharge squib on the APU fire extinguisher bottle.Arms the discharge squib on the APU fire extinguisher bottle.• Closes APU fuel shutoff valve, APU fuel solenoid valve, APU bleed air valve, and APU air inlet door.Closes APU fuel shutoff valve, APU fuel solenoid valve, APU bleed air valve, and APU air inlet door.• Trips the generator control relay and circuit breaker.Trips the generator control relay and circuit breaker.• Provides a backup for the automatic shutdown feature.Provides a backup for the automatic shutdown feature. Rotating the APU fire warning switch left or right will discharge the APU fire bottle extinguishing Rotating the APU fire warning switch left or right will discharge the APU fire bottle extinguishing agent into the APU shroud.agent into the APU shroud.



OVHT DET Switches (Three-position):OVHT DET Switches (Three-position):NORMAL –NORMAL –Both overheat/fire detector loops (“A” and “B”) are active.Both overheat/fire detector loops (“A” and “B”) are active.

““A” –A” –Overheat/fire detector loop “A” is the selected active loop on respective engine.Overheat/fire detector loop “A” is the selected active loop on respective engine.

““B” –B” –Overheat/fire detector loop “B” is the selected active loop on respective engine.Overheat/fire detector loop “B” is the selected active loop on respective engine.



FAULT/INOP and OVHT/FIRE TEST Switch (spring-loaded to center):FAULT/INOP and OVHT/FIRE TEST Switch (spring-loaded to center):FAULT/INOP – FAULT/INOP – Tests the fault detection circuits for both engines and the APU.Tests the fault detection circuits for both engines and the APU.

OVHT/FIRE – OVHT/FIRE – Tests both overheat/fire detection loops (“A” and “B”) on both engines. Also tests the APU and Tests both overheat/fire detection loops (“A” and “B”) on both engines. Also tests the APU and wheel well fire detector loops.wheel well fire detector loops.

Note: A detailed description of the FAULT/INOP and OVHT/FIRE test will be discussed later in Note: A detailed description of the FAULT/INOP and OVHT/FIRE test will be discussed later in this presentation.this presentation.



BELL CUTOUT Switch:BELL CUTOUT Switch:Push –Push –• Extinguishes both FIRE WARN lights.Extinguishes both FIRE WARN lights.• Silences fire warning bell.Silences fire warning bell.• Silences remote APU fire warning horn (only if aircraft on the ground).Silences remote APU fire warning horn (only if aircraft on the ground).• Resets fire warning system for additional fire warnings.Resets fire warning system for additional fire warnings.



EXT TEST Switch (spring-loaded to center):EXT TEST Switch (spring-loaded to center):When positioned to 1 or 2, tests to ensure circuit continuity is normal from the engine and APU When positioned to 1 or 2, tests to ensure circuit continuity is normal from the engine and APU fire extinguisher bottle squibs to the respective fire warning switch.fire extinguisher bottle squibs to the respective fire warning switch.

Note: All fire extinguisher bottle squibs are powered by the hot battery bus.Note: All fire extinguisher bottle squibs are powered by the hot battery bus.


Overheat/Fire Protection PanelOverheat/Fire Protection Panel- Lights -- Lights -

ENG 1 OVERHEAT and ENG 2 OVERHEAT Lights:ENG 1 OVERHEAT and ENG 2 OVERHEAT Lights:Illuminated –Illuminated –• Indicates an overheat condition in the respective engine.Indicates an overheat condition in the respective engine.• Automatically unlocks respective engine fire warning switch.Automatically unlocks respective engine fire warning switch.• MASTER CAUTION and OVHT/DET system annunciator lights illuminate.MASTER CAUTION and OVHT/DET system annunciator lights illuminate.

Note: The ENG OVERHEAT lights also illuminate during an OVHT/FIRE test.Note: The ENG OVERHEAT lights also illuminate during an OVHT/FIRE test.



WHEEL WELL Fire Warning Light:WHEEL WELL Fire Warning Light:Illuminated –Illuminated –• Indicates a fire in the main gear wheel well.Indicates a fire in the main gear wheel well.• FIRE WARN lights illuminate.FIRE WARN lights illuminate.• Fire warning bell sounds.Fire warning bell sounds.

Note: The WHEEL WELL fire warning light also illuminates during an OVHT/FIRE test if the Note: The WHEEL WELL fire warning light also illuminates during an OVHT/FIRE test if the wheel well fire loop is normal (see note below).wheel well fire loop is normal (see note below).

Note: The fire detector loop in the wheel well is AC powered (transfer bus 1). Therefore, AC Note: The fire detector loop in the wheel well is AC powered (transfer bus 1). Therefore, AC power on the aircraft is required to detect a wheel well fire and to test the wheel well fire power on the aircraft is required to detect a wheel well fire and to test the wheel well fire detector loop. Also, the nose gear wheel well does not incorporate a fire detection system.detector loop. Also, the nose gear wheel well does not incorporate a fire detection system.



FAULT Light:FAULT Light:Illuminated –Illuminated –• Indicates Indicates bothboth overheat/fire detector loops (“A” and “B”) have failed on an engine (with related overheat/fire detector loops (“A” and “B”) have failed on an engine (with related OVHT DET switch in NORMAL). OVHT DET switch in NORMAL). • Indicates the selected overheat/fire detector loop (“A” or “B”) has failed on one engine (with Indicates the selected overheat/fire detector loop (“A” or “B”) has failed on one engine (with related OVHT DET switch in “A” or “B”).related OVHT DET switch in “A” or “B”).• During an OVHT/FIRE test, indicates an overheat/fire detector loop(s) (“A” or “B”) has failed on During an OVHT/FIRE test, indicates an overheat/fire detector loop(s) (“A” or “B”) has failed on one or both engines (with related OVHT DET switch in NORMAL).one or both engines (with related OVHT DET switch in NORMAL).

Note: FAULT light also illuminates during a FAULT/INOP test if fault detection circuits are Note: FAULT light also illuminates during a FAULT/INOP test if fault detection circuits are normal.normal.

Note: The MASTER CAUTION and OVHT/DET system annunciator lights Note: The MASTER CAUTION and OVHT/DET system annunciator lights DO NOTDO NOT illuminate when illuminate when the FAULT light illuminates.the FAULT light illuminates.



APU DET INOP Light:APU DET INOP Light:Illuminated –Illuminated –• Indicates APU fire detector loop has failed.Indicates APU fire detector loop has failed.• MASTER CAUTION and OVHT/DET system annunciator lights illuminate.MASTER CAUTION and OVHT/DET system annunciator lights illuminate.

Note: APU DET INOP light also illuminates during a FAULT/INOP test if the APU fire detector loop Note: APU DET INOP light also illuminates during a FAULT/INOP test if the APU fire detector loop is normal.is normal.



APU BOTTLE DISCHARGED Light:APU BOTTLE DISCHARGED Light:Illuminated –Illuminated –Indicates APU fire extinguisher bottle has discharged.Indicates APU fire extinguisher bottle has discharged.

Note: The MASTER CAUTION system does not illuminate when the APU BOTTLE DISCHARGED Note: The MASTER CAUTION system does not illuminate when the APU BOTTLE DISCHARGED light illuminates.light illuminates.



L and R BOTTLE DISCHARGED Lights:L and R BOTTLE DISCHARGED Lights:Illuminated –Illuminated –Indicates respective engine fire extinguisher bottle has discharged.Indicates respective engine fire extinguisher bottle has discharged.

Note: The MASTER CAUTION system does not illuminate when the L or R BOTTLE DISCHARGED Note: The MASTER CAUTION system does not illuminate when the L or R BOTTLE DISCHARGED lights illuminates.lights illuminates.



EXT TEST Lights (3 green):EXT TEST Lights (3 green):Illuminated –Illuminated –Extinguisher test switch has been positioned to 1 or 2 and circuit continuity is normal from the Extinguisher test switch has been positioned to 1 or 2 and circuit continuity is normal from the engine and APU fire extinguisher bottle squibs to the respective fire warning switch.engine and APU fire extinguisher bottle squibs to the respective fire warning switch.


Overheat/Fire Protection PanelOverheat/Fire Protection Panel(side view)(side view)

Fire Warning Switch Override:Fire Warning Switch Override:One located under each fire warning switch.One located under each fire warning switch.

Push –Push –Manually unlocks the respective fire warning Manually unlocks the respective fire warning switch, which then allows the switch to be switch, which then allows the switch to be “pulled-up.” This action may be necessary if “pulled-up.” This action may be necessary if the switch fails to unlock during an engine the switch fails to unlock during an engine overheat or fire condition.overheat or fire condition.


Fire Warning SystemFire Warning SystemFIRE WARN lights:FIRE WARN lights:Illuminated –Illuminated –• Indicates a fire warning in the engine(s), main Indicates a fire warning in the engine(s), main

gear wheel well, or APU. Lights remain gear wheel well, or APU. Lights remain illuminated as long as the fire condition exists or illuminated as long as the fire condition exists or

until the crew resets the fire warning system.until the crew resets the fire warning system.• A fire system test is being performed.A fire system test is being performed.• Fire warning bell sounds.Fire warning bell sounds.• Remote APU fire warning horn sounds during an Remote APU fire warning horn sounds during an

APU fire if the aircraft is on the ground.APU fire if the aircraft is on the ground.

Push –Push –• Extinguishes both FIRE WARN lights.Extinguishes both FIRE WARN lights.• Silences fire warning bell.Silences fire warning bell.• Silences remote APU fire warning horn Silences remote APU fire warning horn (ground only).(ground only).• Resets fire warning system for additional fire Resets fire warning system for additional fire

warnings.warnings.

Note: Pushing the BELL CUTOUT switch on the Note: Pushing the BELL CUTOUT switch on the overheat/fire protection panel results in the same overheat/fire protection panel results in the same four items listed above.four items listed above.

Left SideLeft Side

Right SideRight Side

Listen to theListen to thefire warning bellfire warning bell

Listen to the APUListen to the APUfire warning hornfire warning horn


APU Ground Control Panel and APU Ground Control Panel and Fire Warning HornFire Warning Horn

Located in the main gear wheel Located in the main gear wheel wellwell



APU Fire Warning HORN CUTOUT Switch:APU Fire Warning HORN CUTOUT Switch:Push –Push –• APU fire warning light (on ground control panel) APU fire warning light (on ground control panel)

stops flashing, but remains illuminated steady stops flashing, but remains illuminated steady until the APU fire detector loop no longer detects until the APU fire detector loop no longer detects a fire condition.a fire condition.• Extinguishes both FIRE WARN lights.Extinguishes both FIRE WARN lights.• Silences fire warning bell in flight deck.Silences fire warning bell in flight deck.• Silences remote APU fire warning horn.Silences remote APU fire warning horn.• Resets fire warning system for additional fire Resets fire warning system for additional fire

warnings.warnings.



APU Fire Control Handle:APU Fire Control Handle:The normal position for the APU fire control handle The normal position for the APU fire control handle is “up.”is “up.”

The following is a list of items that occur when the The following is a list of items that occur when the APU fire control handle is “pulled-down”: APU fire control handle is “pulled-down”: • Closes APU fuel shutoff valve, APU fuel solenoid Closes APU fuel shutoff valve, APU fuel solenoid

valve, APU bleed air valve, and APU air inlet door.valve, APU bleed air valve, and APU air inlet door.• Trips the generator control relay and circuit Trips the generator control relay and circuit

breaker.breaker.• Arms the APU BOTTLE DISCHARGE switch.Arms the APU BOTTLE DISCHARGE switch.



APU BOTTLE DISCHARGE Switch:APU BOTTLE DISCHARGE Switch:(spring-loaded to center)(spring-loaded to center)

Once the APU BOTTLE DISCHARGE switch is Once the APU BOTTLE DISCHARGE switch is armed, toggling the switch (left or right) will armed, toggling the switch (left or right) will discharge the APU fire bottle extinguishing agent discharge the APU fire bottle extinguishing agent into the APU shroud.into the APU shroud.

Note: The APU BOTTLE DISCHARGE switch can Note: The APU BOTTLE DISCHARGE switch can onlyonly be armed by “pulling-down” on APU fire be armed by “pulling-down” on APU fire control handle. “Pulling-up” on the APU fire control handle. “Pulling-up” on the APU fire warning switch it the flight deck does not arm the warning switch it the flight deck does not arm the APU BOTTLE DISCHARGE switch.APU BOTTLE DISCHARGE switch.



APU Fire Warning Light:APU Fire Warning Light:Illuminated flashing –Illuminated flashing –Indicates a fire condition exists in the APU.Indicates a fire condition exists in the APU.

Recall that with an APU fire indication, the Recall that with an APU fire indication, the following items also occur:following items also occur:• Automatically unlocks APU fire warning switch.Automatically unlocks APU fire warning switch.• FIRE WARN lights illuminate.FIRE WARN lights illuminate.• Fire warning bell sounds.Fire warning bell sounds.• APU fire warning horn in main gear wheel well APU fire warning horn in main gear wheel well

sounds (if aircraft is on the ground).sounds (if aircraft is on the ground).

Illuminated steady –Illuminated steady –Indicates APU fire warning HORN CUTOUT switch Indicates APU fire warning HORN CUTOUT switch has been pushed following an APU fire indication. has been pushed following an APU fire indication. Light remains illuminated steady until the APU fire Light remains illuminated steady until the APU fire detector loop no longer detects a fire condition.detector loop no longer detects a fire condition.



APU Fire Warning Horn:APU Fire Warning Horn:• Gives aural warning of fire condition in the APU.Gives aural warning of fire condition in the APU.• Horn is silenced by pushing the APU fire warning Horn is silenced by pushing the APU fire warning

HORN CUTOUT switch.HORN CUTOUT switch.• Horn is active Horn is active onlyonly when aircraft is on the ground. when aircraft is on the ground.

Horn is deactivated while in flight.Horn is deactivated while in flight.

Listen to the APUListen to the APUfire warning hornfire warning horn


Lavatory Fire Extinguisher Bottle Lavatory Fire Extinguisher Bottle and Temperature Indicatorand Temperature Indicator

Located under the lavatory sinksLocated under the lavatory sinks



Lavatory Fire Extinguisher Bottle:Lavatory Fire Extinguisher Bottle:This fire bottle is a steel container with a diameter This fire bottle is a steel container with a diameter of approximately 2.5 inches. The bottle is filled of approximately 2.5 inches. The bottle is filled with approximately 10 cubic inches of Freon.with approximately 10 cubic inches of Freon.



Lavatory Fire Extinguisher Bottle:Lavatory Fire Extinguisher Bottle:Two discharge tubes extend from the bottom of the Two discharge tubes extend from the bottom of the fire bottle. One discharge tube terminates in the fire bottle. One discharge tube terminates in the towel waste compartment and the other tube towel waste compartment and the other tube terminates under the lavatory sink. At the end of terminates under the lavatory sink. At the end of each discharge tube is a fusible tip with a melting each discharge tube is a fusible tip with a melting temperature of 174temperature of 174° F. When the temperature in ° F. When the temperature in the towel waste compartment or under the lavatory the towel waste compartment or under the lavatory sink exceeds sink exceeds 174174° F, the associated fusible tip will ° F, the associated fusible tip will melt and consequently the bottle discharges into melt and consequently the bottle discharges into the affected area. The fusible tips will change the affected area. The fusible tips will change color from black to silver to indicate the bottle has color from black to silver to indicate the bottle has discharged.discharged.

Note: There is no indication in the flight deck that Note: There is no indication in the flight deck that the lavatory fire extinguisher bottle has the lavatory fire extinguisher bottle has discharged. Also, on some aircraft, both discharge discharged. Also, on some aircraft, both discharge tubes may terminate in the towel waste tubes may terminate in the towel waste compartment.compartment.



Temperature Indicator Placard:Temperature Indicator Placard:The temperature indicator placard is a thin vinyl The temperature indicator placard is a thin vinyl plate containing four heat sensitive patches. The plate containing four heat sensitive patches. The patches will change from white to black in color patches will change from white to black in color when the placard is exposed to temperatures from when the placard is exposed to temperatures from 180180° F to ° F to 250250° F.° F.

This concludes the general review of the fire protection system. The nextThis concludes the general review of the fire protection system. The nextsection will discuss the fire protection system in greater detail. Click section will discuss the fire protection system in greater detail. Click NextNext to continue. to continue.


Fire ProtectionSystem Description

The engines, APU, main gear wheel well, and lavatories all incorporate a fire detection system. The engines also incorporate an overheat detection system. All the aforementioned areas

have their own fire extinguishing system, except the main gear wheel well.


Engine Overheat and Fire DetectionEngine Overheat and Fire Detection

The engine overheat/fire detection system is known as a “dual-loop” system. This The engine overheat/fire detection system is known as a “dual-loop” system. This “dual-loop” system consists of two identical overheat/fire detector loops. Both loops “dual-loop” system consists of two identical overheat/fire detector loops. Both loops are capable of detecting an overheat or fire condition. The loops are referred to as loop are capable of detecting an overheat or fire condition. The loops are referred to as loop “A” and loop “B.”“A” and loop “B.”



Loop “A” and loop “B” both consist of four sensing elements. Each sensing element is Loop “A” and loop “B” both consist of four sensing elements. Each sensing element is part of a continuous electrical resistance loop, with resistance varying inversely as a part of a continuous electrical resistance loop, with resistance varying inversely as a function of temperature. In other words, as the temperature of the sensing element function of temperature. In other words, as the temperature of the sensing element increases, resistance decreases. The sensing elements run side-by-side and are attached increases, resistance decreases. The sensing elements run side-by-side and are attached to a support tube. The power source for both overheat/fire detector loops is the battery to a support tube. The power source for both overheat/fire detector loops is the battery bus.bus.

The four sensing elements are located in the following four areas of the engine: engine The four sensing elements are located in the following four areas of the engine: engine strut, upper fan, lower fan, and surrounding engine corestrut, upper fan, lower fan, and surrounding engine core

Engine strut Engine strut elementelement

Upper fan Upper fan elementelement

Lower fan Lower fan elementelement

Element Element surrounding surrounding engine coreengine core

See picture of See picture of upper fan elementupper fan element



With the OVHT DET switches positioned to NORMAL, With the OVHT DET switches positioned to NORMAL, bothboth loop “A” and loop “B” sensing loop “A” and loop “B” sensing elements must agree on a overheat condition before an overheat signal is sent to the flight elements must agree on a overheat condition before an overheat signal is sent to the flight deck. deck.

With the OVHT DET switch positioned to “A” or “B,” the system operates as a single loop With the OVHT DET switch positioned to “A” or “B,” the system operates as a single loop system. The selected loop will operate normally without the assistance of the non-selected system. The selected loop will operate normally without the assistance of the non-selected loop and, if necessary, will send an overheat signal to the flight deck if it detects an overheat loop and, if necessary, will send an overheat signal to the flight deck if it detects an overheat condition. condition.

The pictures above indicate which lights will be illuminated during an overheat condition on the The pictures above indicate which lights will be illuminated during an overheat condition on the No. 1 engine. The ENG 1 OVERHEAT light will remain illuminated until the temperature of the No. 1 engine. The ENG 1 OVERHEAT light will remain illuminated until the temperature of the detector loops drop below the pre-determined limit.detector loops drop below the pre-determined limit.



With the OVHT DET switches positioned to NORMAL, With the OVHT DET switches positioned to NORMAL, bothboth loop “A” and loop “B” sensing loop “A” and loop “B” sensing elements must agree on a fire condition before a fire signal is sent to the flight deck. elements must agree on a fire condition before a fire signal is sent to the flight deck.

With the OVHT DET switch positioned to “A” or “B,” the system operates as a single loop With the OVHT DET switch positioned to “A” or “B,” the system operates as a single loop system. The selected loop will operate normally without the assistance of the non-selected system. The selected loop will operate normally without the assistance of the non-selected loop and, if necessary, will send a fire signal to the flight deck if it detects a fire condition. loop and, if necessary, will send a fire signal to the flight deck if it detects a fire condition.

The pictures above indicate which lights will be illuminated during a fire condition on the The pictures above indicate which lights will be illuminated during a fire condition on the No. 1 engine. The engine fire warning switch and ENG 1 OVERHEAT light will remain No. 1 engine. The engine fire warning switch and ENG 1 OVERHEAT light will remain illuminated until the temperature of the detector loops drop below the pre-determined limit.illuminated until the temperature of the detector loops drop below the pre-determined limit.



Recall that the FAULT light monitors both loop “A” and “B” on both engines. With a failure Recall that the FAULT light monitors both loop “A” and “B” on both engines. With a failure of one loop on either engine, and the OVHT DET switches in NORMAL, the affected loop is of one loop on either engine, and the OVHT DET switches in NORMAL, the affected loop is automatically “deselected” and the system operates as a single loop system. The crew will automatically “deselected” and the system operates as a single loop system. The crew will still be warned of an overheat or fire condition even with one loop inoperative. There is no still be warned of an overheat or fire condition even with one loop inoperative. There is no flight deck indication of a single loop failure, i.e. the FAULT light flight deck indication of a single loop failure, i.e. the FAULT light does notdoes not illuminate. illuminate.

If both loop “A” and “B” were to fail on either engine, the FAULT illuminates. The failure of If both loop “A” and “B” were to fail on either engine, the FAULT illuminates. The failure of both loops renders the overheat/fire detection system inoperative on the affected engine. both loops renders the overheat/fire detection system inoperative on the affected engine. The illumination of the FAULT light The illumination of the FAULT light does notdoes not illuminate the master caution or any system illuminate the master caution or any system annunciator.annunciator.


Overheat, Fire, and Fault Light LogicOverheat, Fire, and Fault Light Logic

This table indicates which overheat/fire detection warning lights will be illuminated under various This table indicates which overheat/fire detection warning lights will be illuminated under various conditions assuming both loops are operative. For example, if loop “A” on the No. 1 engine was conditions assuming both loops are operative. For example, if loop “A” on the No. 1 engine was detecting an overheat condition and loop “B” on the No. 1 engine was detecting a fire condition, the detecting an overheat condition and loop “B” on the No. 1 engine was detecting a fire condition, the ENG 1 OVERHEAT light would be illuminated. This is because ENG 1 OVERHEAT light would be illuminated. This is because bothboth loops have at least agreed upon loops have at least agreed upon an overheat condition, yet do not agree on a fire condition.an overheat condition, yet do not agree on a fire condition.

LOOP “A”LOOP “A”

LLOOOOPP

““B”B”

LOOP LOOP CONDITIONCONDITION FIREFIRE OVERHEATOVERHEAT NORMALNORMAL FAULTFAULT POWER POWER

FAILUREFAILURE

FIREFIRE FIREFIREOVERHEATOVERHEAT OVERHEATOVERHEAT NONENONE FIREFIRE

OVERHEATOVERHEAT FAULTFAULT

OVERHEATOVERHEAT OVERHEATOVERHEAT OVERHEATOVERHEAT NONENONE OVERHEATOVERHEAT FAULTFAULT

NORMALNORMAL NONENONE NONENONE NONENONE NONENONE FAULTFAULT

FAULTFAULT FIREFIREOVERHEATOVERHEAT OVERHEATOVERHEAT NONENONE FAULTFAULT FAULTFAULT

POWER POWER FAILUREFAILURE FAULTFAULT FAULTFAULT FAULTFAULT FAULTFAULT FAULTFAULT


Overheat, Fire, and Fault Light LogicOverheat, Fire, and Fault Light Logic

This table indicates which overheat/fire detection warning lights will be illuminated under various This table indicates which overheat/fire detection warning lights will be illuminated under various conditions assuming one loop inoperative. For example, if loop “A” on the No. 1 engine was conditions assuming one loop inoperative. For example, if loop “A” on the No. 1 engine was inoperative and loop “B” on the No. 1 engine was sensing a fire condition, the No. 1 fire warning switch inoperative and loop “B” on the No. 1 engine was sensing a fire condition, the No. 1 fire warning switch and the ENG 1 OVERHEAT light would be illuminated. Because one loop is inoperative, the operating and the ENG 1 OVERHEAT light would be illuminated. Because one loop is inoperative, the operating loop acts as a single loop system and sends the appropriate warning signals to the fight deck.loop acts as a single loop system and sends the appropriate warning signals to the fight deck.

OPERATING OPERATING LOOP LOOP

CONDITIONCONDITIONFIREFIRE OVERHEATOVERHEAT NORMALNORMAL FAULTFAULT POWER POWER

FAILUREFAILURE

FLIGHT DECK FLIGHT DECK INDICATIONINDICATION

FIREFIREOVERHEATOVERHEAT OVERHEATOVERHEAT NONENONE FAULTFAULT FAULTFAULT


Engine Fire ExtinguishingEngine Fire Extinguishing

In order to combat an engine fire, the respective fire warning switch must be “pulled-up” and In order to combat an engine fire, the respective fire warning switch must be “pulled-up” and rotated left or right. The fire warning switches are normally locked down to prevent an rotated left or right. The fire warning switches are normally locked down to prevent an inadvertent shutdown of an engine. They are automatically unlocked when the system detects inadvertent shutdown of an engine. They are automatically unlocked when the system detects an overheat or fire condition. If the fire warning switches fail to unlock, they may be manually an overheat or fire condition. If the fire warning switches fail to unlock, they may be manually unlocked via the fire warning switch override (located under each fire warning switch).unlocked via the fire warning switch override (located under each fire warning switch).



The following is a list of items that occur when an engine fire warning switch is “pulled-up”: The following is a list of items that occur when an engine fire warning switch is “pulled-up”: • Allows the engine fire warning switch to be rotated.Allows the engine fire warning switch to be rotated.• Arms one discharge squib on each engine fire extinguisher bottle.Arms one discharge squib on each engine fire extinguisher bottle.• Closes respective engine fuel shutoff valve, hydraulic shutoff valve, and engine bleed air valve.Closes respective engine fuel shutoff valve, hydraulic shutoff valve, and engine bleed air valve.• Trips the respective generator control relay and circuit breaker.Trips the respective generator control relay and circuit breaker.• Thrust reverser isolation valve closes, thereby disabling the thrust reverser.Thrust reverser isolation valve closes, thereby disabling the thrust reverser.• Deactivates the respective engine driven pump hydraulic LOW PRESSURE light.Deactivates the respective engine driven pump hydraulic LOW PRESSURE light.



There are two engine fire bottles located in the main gear wheel well. Either or both fire bottles There are two engine fire bottles located in the main gear wheel well. Either or both fire bottles are capable of discharging their extinguishing agent to either engine. Two squib cartridges are are capable of discharging their extinguishing agent to either engine. Two squib cartridges are attached to the discharge ports of both fire bottles. Rotating an engine fire warning switch attached to the discharge ports of both fire bottles. Rotating an engine fire warning switch “fires” the appropriate squib on the selected bottle, which in turn ruptures a retaining disc and “fires” the appropriate squib on the selected bottle, which in turn ruptures a retaining disc and releases the extinguishing agent into the respective engine. When the pressure in the fire bottle releases the extinguishing agent into the respective engine. When the pressure in the fire bottle drops below a pre-determined limit, the respective BOTTLE DISCHARGED light illuminates.drops below a pre-determined limit, the respective BOTTLE DISCHARGED light illuminates.

See picture of See picture of engine fire bottlesengine fire bottles


Engine Fire ExtinguishingEngine Fire ExtinguishingEngine Fire ExtinguishingLet’s assume that an engine fire exists on the No. 1 engine…

Rotating the No. 1 engine fire warning switch to the left electrically “fires” the No. 1 squib on the left bottle and discharges the extinguishing agent into the No. 1 engine. If the engine fire does not extinguish, the other option is to rotate the No. 1 engine fire warning switch to the right. This “fires” the No. 1 squib on the right bottle and discharges the extinguishing agent into the No. 1 engine. Remember, ONLY two engine fire extinguishing bottles are installed!

Rotating the No. 2 engine fire warning switch acts in the same manner as the No. 1 engine fire warning switch, except the extinguishing agent is discharged into the No. 2 engine.

LeftLeftfirefire

bottlebottle

RightRightfirefire

bottlebottle

No. 1 engine No. 2 engine

No. 2 squib

No. 1 squib

No. 2 squib

No. 1 squib


APU Fire DetectionAPU Fire Detection

A single fire detector loop is installed on the APU and consists of three sensing elements. A single fire detector loop is installed on the APU and consists of three sensing elements. The sensing elements are located in the APU engine and exhaust areas. The sensing The sensing elements are located in the APU engine and exhaust areas. The sensing elements function similar to the engine overheat/fire detector loops, i.e. as the elements function similar to the engine overheat/fire detector loops, i.e. as the temperature of the sensing element increases, resistance decreases. The power source temperature of the sensing element increases, resistance decreases. The power source for the fire detector loop is the battery bus.for the fire detector loop is the battery bus.



When the temperature of the sensing element rises to a pre-When the temperature of the sensing element rises to a pre-determined limit, the APU fire warning switch illuminates, the fire determined limit, the APU fire warning switch illuminates, the fire warning bell sounds, and the APU automatically shuts down. warning bell sounds, and the APU automatically shuts down. These pictures indicate which lights will be illuminated during an These pictures indicate which lights will be illuminated during an APU fire condition. In addition, the APU fire warning light on the APU fire condition. In addition, the APU fire warning light on the ground control panel flashes and the APU fire warning horn ground control panel flashes and the APU fire warning horn sounds (if aircraft is on the ground).sounds (if aircraft is on the ground).

The APU fire warning switch and the APU fire warning light will The APU fire warning switch and the APU fire warning light will remain illuminated until the temperature of the detector loop remain illuminated until the temperature of the detector loop drops below the pre-determined limit.drops below the pre-determined limit.



A fault monitoring system is installed to ensure that the APU fire detector loop is A fault monitoring system is installed to ensure that the APU fire detector loop is functioning properly. If the loop fails, the APU DET INOP light illuminates as well as the functioning properly. If the loop fails, the APU DET INOP light illuminates as well as the MASTER CAUTION and OVHT/DET system annunciator.MASTER CAUTION and OVHT/DET system annunciator.


APU Fire ExtinguishingAPU Fire Extinguishing

In order to combat an APU fire, the APU fire warning switch must be “pulled-up” and In order to combat an APU fire, the APU fire warning switch must be “pulled-up” and rotated left or right. The APU fire warning switch is normally locked down to prevent an rotated left or right. The APU fire warning switch is normally locked down to prevent an inadvertent shutdown of the APU. It is automatically unlocked when the system detects a inadvertent shutdown of the APU. It is automatically unlocked when the system detects a fire condition in the APU. If the fire switch fails to unlock, it may be manually unlocked via fire condition in the APU. If the fire switch fails to unlock, it may be manually unlocked via the fire warning switch override (located under the APU fire warning switch).the fire warning switch override (located under the APU fire warning switch).



The following is a list of items that occur when the APU fire warning switch is “pulled-up”: The following is a list of items that occur when the APU fire warning switch is “pulled-up”: • Allows the APU fire warning switch to be rotated.Allows the APU fire warning switch to be rotated.• Provides a backup for the automatic shutdown feature.Provides a backup for the automatic shutdown feature.• Closes APU fuel shutoff valve, APU fuel solenoid valve, APU bleed air valve, and APU air inlet Closes APU fuel shutoff valve, APU fuel solenoid valve, APU bleed air valve, and APU air inlet door.door.• Trips the generator control relay and circuit breaker.Trips the generator control relay and circuit breaker.• Arms the discharge squib on the APU fire extinguisher bottle.Arms the discharge squib on the APU fire extinguisher bottle.



There is one APU fire extinguisher bottle located in the empennage section of the aircraft. There is one APU fire extinguisher bottle located in the empennage section of the aircraft. One squib cartridge is attached to the discharge port of the fire bottle. Rotating the APU One squib cartridge is attached to the discharge port of the fire bottle. Rotating the APU fire warning switch “fires” the squib which in turn ruptures a retaining disc and releases fire warning switch “fires” the squib which in turn ruptures a retaining disc and releases the extinguishing agent into the APU. When the pressure in the fire bottle drops below a the extinguishing agent into the APU. When the pressure in the fire bottle drops below a pre-determined limit, the APU BOTTLE DISCHARGED light illuminates.pre-determined limit, the APU BOTTLE DISCHARGED light illuminates.


APU Fire Bottle IndicatorsAPU Fire Bottle Indicators

Located on the lower right side of the fuselage, under the APU air inlet door, are two APU Located on the lower right side of the fuselage, under the APU air inlet door, are two APU fire bottle indicators. The indicators are small red and yellow plastic discs held in place fire bottle indicators. The indicators are small red and yellow plastic discs held in place by a snap-ring. The red disc is the thermal relief indicator and the yellow disc is the by a snap-ring. The red disc is the thermal relief indicator and the yellow disc is the system discharge indicator.system discharge indicator.


APU Fire Bottle IndicatorsAPU Fire Bottle Indicators

If the internal temperature of the fire extinguisher bottle exceeds approximately 266If the internal temperature of the fire extinguisher bottle exceeds approximately 266° F., the ° F., the extinguishing agent will be expelled into a discharge line which leads to the thermal relief extinguishing agent will be expelled into a discharge line which leads to the thermal relief indicator (red disc). The pressure from the bottle will rupture the thermal relief indicator indicator (red disc). The pressure from the bottle will rupture the thermal relief indicator and all the extinguishing agent is dumped overboard.and all the extinguishing agent is dumped overboard.

When the APU fire warning switch is rotated in either direction, the extinguishing agent When the APU fire warning switch is rotated in either direction, the extinguishing agent from the bottle is automatically expelled into the APU shroud. When this occurs, some of from the bottle is automatically expelled into the APU shroud. When this occurs, some of the pressure from the bottle is routed to the system discharge indicator (yellow disc). The the pressure from the bottle is routed to the system discharge indicator (yellow disc). The pressure forces a small “knock-out” pin to punch the yellow disc out onto the ground. The pressure forces a small “knock-out” pin to punch the yellow disc out onto the ground. The “knock-out” pin will protrude slightly from the hole where the yellow disc was.“knock-out” pin will protrude slightly from the hole where the yellow disc was.


Main Gear Wheel Well Fire DetectionMain Gear Wheel Well Fire Detection

A single fire detector loop is installed on the ceiling of the main gear wheel well. The fire A single fire detector loop is installed on the ceiling of the main gear wheel well. The fire detector loop consists of one continuous sensing element that functions similar to the detector loop consists of one continuous sensing element that functions similar to the engine overheat/fire detector loops, i.e. as the temperature of the sensing element engine overheat/fire detector loops, i.e. as the temperature of the sensing element increases, resistance decreases. The power source for the fire detector loop is transfer bus increases, resistance decreases. The power source for the fire detector loop is transfer bus 1. The nose gear wheel well does not incorporate a fire detection system.1. The nose gear wheel well does not incorporate a fire detection system.

See picture of main gearSee picture of main gearwheel well fire loopwheel well fire loop


Main Gear Wheel Well Fire DetectionMain Gear Wheel Well Fire Detection

When the temperature of the sensing element rises to a pre-determined limit, the WHEEL When the temperature of the sensing element rises to a pre-determined limit, the WHEEL WELL fire warning light illuminates and the fire warning bell sounds. These pictures WELL fire warning light illuminates and the fire warning bell sounds. These pictures indicate which lights will be illuminated during a wheel well fire condition.indicate which lights will be illuminated during a wheel well fire condition.

The WHEEL WELL fire warning light will remain illuminated until the temperature of the fire The WHEEL WELL fire warning light will remain illuminated until the temperature of the fire detector loop drops below the pre-determined limit.detector loop drops below the pre-determined limit.

Note: The main gear wheel well detection system does not incorporate any type of fire Note: The main gear wheel well detection system does not incorporate any type of fire extinguishing system.extinguishing system.


FAULT/INOP TestFAULT/INOP Test

The fault detection circuits for both engines and the APU are tested by pushing and holding the TEST The fault detection circuits for both engines and the APU are tested by pushing and holding the TEST switch to the FAULT/INOP position. The picture above and the list below indicates which lights will be switch to the FAULT/INOP position. The picture above and the list below indicates which lights will be illuminated during a illuminated during a successfulsuccessful FAULT/INOP test: FAULT/INOP test:• The FAULT light illuminates.The FAULT light illuminates.• The APU DET INOP light illuminates.The APU DET INOP light illuminates.• The OVHT/DET system annunciator light illuminates The OVHT/DET system annunciator light illuminates (due to the illumination of the APU DET INOP light)(due to the illumination of the APU DET INOP light)..• Both MASTER CAUTION lights illuminate.Both MASTER CAUTION lights illuminate.


FAULT/INOP TestFAULT/INOP Test

When the FAULT/INOP test switch is released, the FAULT and APU DET INOP lights extinguish. The When the FAULT/INOP test switch is released, the FAULT and APU DET INOP lights extinguish. The MASTER CAUTION and OVHT/DET system annunciator lights extinguish when either MASTER MASTER CAUTION and OVHT/DET system annunciator lights extinguish when either MASTER CAUTION light is pressed.CAUTION light is pressed.

If the FAULT or APU DET INOP lights do not illuminate during the test, the respective fault detection If the FAULT or APU DET INOP lights do not illuminate during the test, the respective fault detection circuits are inoperative and the FAULT/INOP test would therefore be considered circuits are inoperative and the FAULT/INOP test would therefore be considered unsuccessful.unsuccessful.


OVHT/FIRE TestOVHT/FIRE Test

To test the overheat/fire detection loops on both engines, the APU fire detector loop, and the main gear To test the overheat/fire detection loops on both engines, the APU fire detector loop, and the main gear wheel well fire detector loop, position the TEST switch to the OVHT/FIRE position. The picture above wheel well fire detector loop, position the TEST switch to the OVHT/FIRE position. The picture above and the list below indicates which lights will be illuminated during a and the list below indicates which lights will be illuminated during a successfulsuccessful OVHT/FIRE test: OVHT/FIRE test:• The fire warning bell sounds.The fire warning bell sounds.• Both engine fire warning switches illuminate.Both engine fire warning switches illuminate.• The APU fire warning switch illuminates.The APU fire warning switch illuminates.• Both ENG OVERHEAT lights illuminate.Both ENG OVERHEAT lights illuminate.• Both MASTER CAUTION lights and both FIRE WARN lights illuminate.Both MASTER CAUTION lights and both FIRE WARN lights illuminate.• The OVHT/DET system annunciator light illuminates The OVHT/DET system annunciator light illuminates (due to the illumination of the ENG OVERHEAT lights)(due to the illumination of the ENG OVERHEAT lights) ..• The WHEEL WELL fire warning light illuminates The WHEEL WELL fire warning light illuminates (if AC power is on the aircraft)(if AC power is on the aircraft)..• The APU fire warning light flashes and the APU fire warning horn sounds The APU fire warning light flashes and the APU fire warning horn sounds (if on the ground)(if on the ground). .



When the OVHT/FIRE test switch is released, the fire warning bell silences and all overheat and When the OVHT/FIRE test switch is released, the fire warning bell silences and all overheat and fire warning lights extinguish. The MASTER CAUTION and OVHT/DET system annunciator fire warning lights extinguish. The MASTER CAUTION and OVHT/DET system annunciator lights extinguish when either MASTER CAUTION light is pressed.lights extinguish when either MASTER CAUTION light is pressed.



During a During a successfulsuccessful OVHT/FIRE test, the FAULT light OVHT/FIRE test, the FAULT light will notwill not illuminate along with the other overheat and illuminate along with the other overheat and fire warning lights. If the FAULT light does illuminate during the OVHT/FIRE test, this indicates that one fire warning lights. If the FAULT light does illuminate during the OVHT/FIRE test, this indicates that one or more detector loops have failed on either engine. The OVHT/FIRE test would therefore be considered or more detector loops have failed on either engine. The OVHT/FIRE test would therefore be considered unsuccessful.unsuccessful. In order to determine which loops on which engine have failed, the OVHT/FIRE test must In order to determine which loops on which engine have failed, the OVHT/FIRE test must be performed again while each OVHT DET switch is positioned to “A” and then “B”. For example, let’s be performed again while each OVHT DET switch is positioned to “A” and then “B”. For example, let’s assume that loop “A” is inoperative on the No. 1 engine. When the OVHT/FIRE test is performed with assume that loop “A” is inoperative on the No. 1 engine. When the OVHT/FIRE test is performed with both OVHT DET switches in “A,” all overheat and fire warning lights illuminate normally both OVHT DET switches in “A,” all overheat and fire warning lights illuminate normally exceptexcept for the for the ENG 1 OVERHEAT and the No. 1 fire warning switch. The FAULT light also illuminates reaffirming that a ENG 1 OVERHEAT and the No. 1 fire warning switch. The FAULT light also illuminates reaffirming that a fault condition exists on the “A” loop, No. 1 engine. The picture above indicates which lights will be fault condition exists on the “A” loop, No. 1 engine. The picture above indicates which lights will be illuminated/extinguished during an OVHT/FIRE test with an inoperative “A” loop, No. 1 engine. Notice the illuminated/extinguished during an OVHT/FIRE test with an inoperative “A” loop, No. 1 engine. Notice the ENG 2 OVERHEAT and No. 2 fire warning switch are illuminated indicating loop “A” No. 2 engine is good.ENG 2 OVERHEAT and No. 2 fire warning switch are illuminated indicating loop “A” No. 2 engine is good.


Extinguisher TestExtinguisher Test

When the extinguisher test switch is positioned to 1 or 2, circuit continuity is tested from the engine When the extinguisher test switch is positioned to 1 or 2, circuit continuity is tested from the engine and APU fire extinguisher bottle squibs to the respective fire warning switch.and APU fire extinguisher bottle squibs to the respective fire warning switch.

All three green extinguisher test lights will illuminate indicating a All three green extinguisher test lights will illuminate indicating a successfulsuccessful test. test.

The following is what occurs when the extinguisher test switch is positioned to 1 and 2:The following is what occurs when the extinguisher test switch is positioned to 1 and 2:Positioned to 1 –Positioned to 1 –Circuit continuity is tested on the No. 1 squib for both the left and right fire extinguisher bottles. Circuit Circuit continuity is tested on the No. 1 squib for both the left and right fire extinguisher bottles. Circuit continuity is also tested for the squib on the APU fire extinguisher bottle.continuity is also tested for the squib on the APU fire extinguisher bottle.Positioned to 2:Positioned to 2:Circuit continuity is tested on the No. 2 squib for both the left and right fire extinguisher bottles. Circuit Circuit continuity is tested on the No. 2 squib for both the left and right fire extinguisher bottles. Circuit continuity is tested continuity is tested againagain for the squib on the APU fire extinguisher bottle. for the squib on the APU fire extinguisher bottle.

b737-300/400 fire protection

Engineering