A. Fire protection consists of fire extinguishing and fire/overheat detection.
B. The detection systems warn of fire or overheat in each engine, auxiliary power unit (APU), main wheel well, wings, lower aft body and lavatories (airplanes with lavatory smoke detection system). Lights on the engine and APU fire control module, master warning lights on the lightshield module, and an alarm bell provide fire indication. On some airplanes, there is a light on the overhead panel in the control cabin which provides fire indication. Additional indications for the APU are a fire warning light on APU ground control panel and a warning horn in the right main wheel well. Lights on the air conditioning module and master caution lights on the lightshield module provide wing/body overheat indication. Lights on the light shield module and on the overhead panel provide lavatory smoke indication (airplanes with lavatory smoke detection system).
C. The extinguishing systems are a fixed engine fire extinguishing system, a fixed APU fire extinguishing system, a fixed lavatory fire extinguishing system, and portable fire extinguishers.
(1) The fixed engine fire extinguishing system consists of two fire extinguisher bottles, providing two-shot extinguishing at either engine. The bottles are connected to each engine by manifolds and tubing. A discharge switch for each engine is on the engine and APU fire control module.
(2) The fixed APU fire extinguishing system consists of an extinguisher bottle connected by tubing to the APU shroud. The APU discharge switches are on the engine and APU fire control module and on the APU ground control panel.
(3) The fixed lavatory fire extinguishing system consists of a heat activated fire extinguisher bottle in each lavatory to extinguish fires under the sink counter and in the towel chute.
(4) Portable fire extinguishers are located in various positions in the crew and passenger cabins. They provide fire extinguishing capability in these cabins and other areas accessible from them.
Engine and APU Fire Control Module
A. The engine and APU fire control module contains components to monitor the fire and overheat detection systems and to control and test the fire extinguishing system. The engine and APU fire control module is on the control stand aft electronic control panel.
B. The front of the module contains the following components for extinguishing and detection: fire switch handles with fire warning lights for each engine and the APU, discharge lights for each engine and APU, overheat lights for each engine, wheel well overheat light, engine detector fault light, fire/overheat detector selector switch for each engine, an APU detector inoperative light, a bell cutout switch, test switches, and three fire extinguisher test lights. Master caution lights control circuits and fire extinguisher bottle test circuits are on cards in the module
A. Fire and overheat detection systems provide aural and visual alerts when overheat or fire is detected.
Engine fire detection
A. The engine fire detection system monitors engine and nacelle temperature for fire and overheat conditions. Dual-loop fire/overheat detectors are in each engine area.
B. The system uses power from the 28-volt dc battery bus. The circuit breakers are on panel.
C. Engine fire detection system components are fire detectors, engine and APU fire detection accessory unit, and engine and APU fire control panel.
Engine Fire/Overheat Detectors
A. A detector consists of two identical sensing elements attached to a support tube by quick-release mounting clamps. Each sensing element is part of a continuous electrical resistance loop, with resistance varying inversely as a function of temperature.
B. As the temperature of the element increases, resistance decreases. When resistance lowers to the first alarm setting, an overheat signal is sent to the control card. When resistance continues to lower to the second setting, a fire alarm signal is sent.
(1) The detectors are identical except for length, temperature trip and reset settings of the pressure switches.
C. The engine fire detectors are in strut, fan upper, fan lower, and engine core areas.
3.Engine and APU Fire Detection Accessory Unit
A.Engine fire detection system components of the engine and APU fire detection accessory unit are engine 1 and 2 control cards and interface logic cards. The unit is on shelf E3-3 of the electronics rack.
B. Control Cards
(1) Each engine has a corresponding control card. These cards constantly monitor and process signals produced by detector loops. The cards send alarm or fault signals to the accessory control card.
C. Interface Logic Cards
(1) The interface logic cards interpret detection control card signals, provide tests, and send fire/overheat warning and fault indication signals to the fire control panel.
4. Engine and APU Fire Control Panel
A. Engine fire detection system components of the engine and APU fire control panel are two fire/overheat detector selector switches, test switch, engine 1 and 2 overheat lights, engine fault light, and engine 1 and 2 fire switch handles. The panel is on the aft electronics panel of the control stand.
B. There is one fire/overheat detector selector switch for each engine. Setting the switch to NORMAL enables both loops to operate in AND - logic. Setting the switch to A or B enables the indicated loop and disables the other.
C. Setting the TEST switch to OVHT/FIRE checks detector continuity, alarm circuit continuity, and integrity of the sensing and warning circuits at a loop resistance equivalent to the alarm temperature level. The engine fire switch handle lights, OVERHEAT lights, master FIRE WARN lights, and bell activate.
(1) Dual-loop fire and overheat detection systems are in each engine area. Both loops of a system must sense fire in order for a fire alarm to be given. If one loop is inoperative, then the system may be set to operate on the operative loop.
APU fire detection
(1) A single-loop fire detection system is in the APU compartment.
A. The APU fire detection system monitors temperature in the compartment and responds to overheat or fire by activating warning lights, alarm bell, and horn, and shutting down the APU.
B. The APU fire detection system uses power from the 28-volt dc battery bus. The system circuit breaker is on circuit breaker panel.
C. The signals from the single detector loop are configured in OR-logic.
D. APU fire indications are lights on the engine and APU fire control panel, master warning lights on the lightshield, and an alarm bell.
E. When the airplane is on the ground, additional APU fire indications are a warning light on the APU ground control panel and a horn in the main wheel well.
2. Engine and APU Fire Control Panel
A. The engine and APU fire control panel is on the pilots' control stand. Components that panel applicable to APU fire detection are APU DET INOP light, fire switch handle warning light, TEST switch, and BELL CUTOUT switch.
(1) AIRPLANES WITH KIDDE OVERHEAT DETECTORS; the DET INOP light provides an indication of short circuit. The DET INOP-light circuitry is also connected to the master caution lights.
(2) AIRPLANES WITH SYSTRON DONNER OVERHEAT DETECTORS; the DET INOP light provides an indication of a wiring fault or sensor loss of pressure. The DET INOP-light circuitry is also connected to the master caution lights.
(3) A fire warning light in the APU fire switch handle provides APU area fire warning. The APU fire warning light is connected to the APU fire detection card. A fire or overheat condition in the APU area will cause steady illumination of the warning light. The fire warning light consists of several bulbs covered by a red translucent plastic lens cap in the fire switch handle.
(4) The TEST switch has three positions: FAULT/INOP-off-FIRE/OVHT; The switch is spring-loaded to the off position. The switch permits testing of the APU fire detection system by checking sensor continuity and simulating a fire condition when positioned to FIRE/OVHT. During fire/overheat test the APU automatic shutdown circuitry is inhibited. When in the FAULT/INOP position, the fault discrimination circuit of the APU fire detection card is tested and the inoperative light will illuminate.
(5) A switch is provided for alarm bell control. Pressing the switch provides 28 volts dc to the signal condition control card in the fire detection accessory unit. The control circuit silences the bell and extinguishes the master fire warning lights.
3. APU Fire Detector Elements
A. Detector elements are in the engine and exhaust areas of the APU. Detector elements are in the engine compartment, exhaust heat shield, and muffler assembly.
B. AIRPLANES WITH KIDDE OVERHEAT DETECTORS; the sensing elements are encased in a perforated tube and are supported by asbestos spacer blocks. Each sensing element is filled with a thermistor material, with resistance varying as a function of temperature.
C. The resistance varies with length. The heating of less than a full length on a sensor will require it to be heated to a higher temperature for the resistance to decrease to the alarm point. This permits the system to integrate the varying temperatures throughout the installation rather than sensing only the highest local temperature. One wire of the sensor is grounded to the outside case of the sensor. The other wire receives power from the detector control unit. The system continuously monitors the resistance between the hot wire and the ground wire.
D. AIRPLANES WITH SYSTRON DONNER OVERHEAT DETECTORS; the sensing elements are attached to a support tube by quick-release mounting clamps. Each sensing element contains an inert gas, a gas-emitting core material, and has a responder on one end. The responder contains two pressure switches, alarm and integrity, and provides the electrical interface with the airplane wiring.
(1) The inert gas in a sensing element expands as temperature increases. The gas-emitting core material expels gas due to high localized temperature. Both actions cause a pressure increase in the element, which causes the alarm pressure switch to close, activating an alarm signal. When the temperature decreases, the pressure decreases, and the alarm switch opens. If a sensing element is damaged and the inert gas leaks, the integrity pressure switch opens, activating a fault signal. The pressure switches provide alarm and integrity signals to the APU fire detection card.
(2) The resistance varies with length. The heating of less than a full length on a sensor will require it to be heated to a higher temperature for the resistance to decrease to the alarm point. This permits the system to integrate the varying temperatures throughout the installation rather than sensing only the highest local temperature. One wire of the sensor is grounded to the outside case of the sensor. The other wire receives power from the detector control unit. The system continuously monitors the resistance between the hot wire and the ground wire.
Wheel well fire detection
(1) A single-loop fire detection system is in the main landing gear wheel well.
A. The wheel well overheat detection system provides overheat detection in the main wheel well area. The detection system is an electrical, heat sensing system that responds to overheat by activating fire warning lights and an alarm bell.
B. The wheel well overheat detection system consists of the engine and APU fire control module, compartment overheat accessory unit, alarm bell, master fire warning lights, and a sensing element. The sensing element is connected to the compartment overheat accessory unit, which monitors the resistance of the sensing element. When a temperature rise causes the element resistance to drop to the value corresponding to the alarm temperature, the compartment overheat accessory unit will provide a signal to the wheel well warning light and alarm bell and a ground to the master fire warning lights.
C. The overheat detection system can be tested by operation of the TEST switch on the engine and APU fire control module. The switch tests continuity through the wheel well system by simulating an overheat condition and energizing the alarm bell and warning lights.
2. Engine and APU Fire Control Module Components
A. Wheel Well Warning Light
(1) A warning light indicates overheat in the wheel well area.
B. Test Switch
(1) Holding the switch to the fire position operates control circuits in the accessory unit which simulate overheat in the wheel well. The wheel well overheat warning components are then energized.
C. Bell Cutout Switch
(1) The switch can be pressed to silence the fire alarm bell and extinguish the master fire warning lights.
3. Compartment Overheat Accessory Unit Components (Airplanes with Boeing M237 compartment overheat accessory unit)
A. The compartment overheat accessory unit is on electronic equipment rack in the electronic compartment.
B. Temperature Control Unit A4
(1) The temperature control unit plugs into the accessory unit and is held in place by screws. The temperature control unit contains circuitry to continuously monitor the sensing element resistance and provide an alarm signal when the element resistance drops to the trip level. When the overheat condition has passed, the system returns to its standby condition.
Wing and lower aft body overheat detection
(1) Two single-loop overheat detection systems are in the wings, the air conditioning bays, the aft cargo compartment, the keel beam, and the APU area.
A. The wing and lower aft body overheat detection system provides overheat detection for the wings and lower aft body. The detection system is an electrical, heat sensing system that responds to overheat by activating warning lights.
B. Airplanes with compartment overheat accessory unit:
(1) The wing and lower aft body overheat detection system consists of an overheat test switch and overheat lights on air conditioning module, compartment overheat accessory unit, master caution lights, and sensing elements. The sensing elements are connected to the compartment overheat accessory unit. The accessory unit contains left and right temperature control units and test circuits. The temperature control units monitor the resistance of the sensing elements. When a temperature rise causes the resistance to drop to value corresponding to the alarm temperature, the temperature control unit will provide a signal to the applicable warning light and the master caution light control section in the air conditioning module.
(2) The wing and lower aft body overheat detection system is divided into left and right sections. The right overheat section consists of sensing elements connected in series with the right temperature control unit and overheat test relay to form a closed circuit sensing loop. The left overheat section consists of sensing elements connected in series through three test switches to the left and APU overheat temperature unit to form a closed circuit sensing loop. Test switches on the compartment overheat accessory unit enable a malfunction in the left overheat section to be isolated.
(3) The overheat detection system can be tested by an overheat test switch on the air conditioning module. The overheat test switch tests continuity through the sensing loops by simulating an overheat condition. If the left detection system fails to test, the area of the malfunction can be isolated by operating the switches on the compartment overheat accessory unit.
(4) The right sensing loop elements are at engine 2 strut cavity, right wing bleed air duct, right wing leading edge, and right air conditioning packs. The left sensing loop elements are at engine 1 strut cavity, left wing bleed air duct, left wing leading edge, left air conditioning packs, keel beam, aft cargo compartment, and APU cavity.
C. Airplanes with electronic Fenwal compartment overheat accessory unit:
(1) The wing and lower aft body overheat detection system consists of an overheat test switch and overheat lights on air conditioning module, compartment overheat accessory unit, master caution lights, and sensing elements. The sensing elements are connected to the compartment overheat accessory unit. The accessory unit contains a control card which has a microprocessor and a relay board which monitor the resistance of the sensing elements. When a temperature rise causes the resistance to drop to a value corresponding to the alarm temperature, the compartment overheat accessory unit will provide a signal to the applicable warning light and the master caution light control section in the air conditioning module. When a alarm/fault condition is found the condition is stored in the non-volatile memory of the Fenwal compartment overheat accessory unit, the MAINT ADV light will illuminate when a condition is stored in memory. The MAINT ADV light will not extinguish until the condition is corrected and the memory is cleared.
(2) The wing and lower aft body overheat detection system is divided into left and right sections. The right overheat section consists of a single detector loop with sensing elements connected in series. The left overheat section consists of four separate detector loops with sensing elements connected in series. All five loops are monitored by the control card in the compartment overheat accessory unit. The compartment overheat accessory unit can isolate an alarm/fault condition to each of the five loops, which can be displayed as a code on the LED display. The codes, as defined on the compartment overheat accessory unit cover plate, isolate the condition to the specific location and condition; an alarm, an open loop fault, or a short circuit loop fault.
(3) The right sensing loop elements are at engine 2 strut cavity, right wing bleed air duct, right wing leading edge, and right air conditioning packs. The left sensing loop elements are at engine 1 strut cavity, left wing bleed air duct, left wing leading edge, left air conditioning packs, keel beam, aft cargo compartment, and APU cavity.
(4) The wing and lower aft body overheat detection system can be tested by an overheat test switch on the air conditioning module. The overheat test switch tests continuity through the sensing loops by simulating an overheat condition.
Lavatory smoke detection
(1) A smoke detector unit is located in each lavatory.
A. A smoke detector is installed in or near the ceiling of each lavatory and is connected to the airplane DC bus number 1. A green indicator light on the detector comes on when power is applied to the detector. The detector monitors the air for presence of smoke or equivalent contaminants. When the concentration of smoke at the sensor gets to a preset threshold, the smoke detector alarm occurs.
B. These are the aural and visual warnings which alert cabin attendants and flight crew in event of a lavatory fire:
(1) Lavatories:
(a) A red alarm light on the smoke detector
(b) AIRPLANES WITHOUT SMOKE DETECTOR MODULE ON THE CABIN ATTENDANT PANEL; a smoke detector horn in the lavatory.
(2) AIRPLANES WITH SMOKE DETECTOR MODULE ON THE CABIN ATTENDANT PANEL; SMOKE DETECTOR panel on the forward cabin attendant panel:
(a) An alarm horn
(b) A SMOKE DETECT light
(c) An applicable lavatory location light
(3) AIRPLANES WITH DETECTORS THAT HAVE SELF TEST CAPABILITY; Passenger Compartment
(a) The lavatory call light on the outside of the lavatory
(b) The attendant call tone
(c) The amber call light next to the applicable exit locator sign
(4) AIRPLANES WITH LAV SMOKE INDICATIONS IN THE FLIGHT COMPARTMENT; Flight Compartment
(a) An amber LAVATORY SMOKE light on the miscellaneous alert section of the forward o verhead panel.
(b) The MASTER CAUTION light
C. Smoke detector switches
(a) The electrical operation of the system can be verified by use of the self test switch. All the alarm indications associated with the detector should come on when the self test switch is pushed.
2. Operation
A. The detection system is activated automatically when power is applied to airplane and system circuit breaker is closed.
B. The smoke detector uses an ionization sensor to detect smoke. A very small amount of radioactive material ionizes the air between two electrodes allowing current to flow through the air between the electrodes. Any smoke particles present interfere with this current flow. The change in current flow is sensed by a current amplifier which outputs a signal to turn on the alarm indicators.