Fire Det. Flashcards
Fire and Overheat Detection
There are three separate areas of protection:
• engine (2 loops)
• APU (2 loops)
• main landing gear (1loop)
Dual loop detection systems are provided for the APU and engines.
A single loop detection system is used to monitor the temperature in the main landing gear (MLG) wheel bins.
Smoke Detection
Both cargo bays are equipped with smoke detectors and a fire extinguishing system. There are three smoke detectors located in the forward cargo bay and two in the aft cargo bay.
The lavatory is protected by a ceiling mounted smoke detector. Fire extinguishing in the waste container is provided.
Engine Fire and Overheat Protection
The engine’s fire and overheat protection system detects fire and/or an overheat conditions in the engine.
For redundancy, each engine area is equipped with two similar detection loops that follow the same path in various areas around and along the engine.
The extinguishing system consists of two bottles. If required both bottles can be discharged into either engine.
Detection Loops
Each engine is protected by dual fire/overheat detection loops. The loops are connected to the FIDEEX unit. The loops are constructed of an outer metal sheathing and two internal wires that are separated by an insulating material (thermistor). One of the wires carries electrical current, the other is grounded to the outer sheathing at the control unit. The resistance of the thermistor decreases with an increase in temperature.
When the electrical resistance decreases to a trip point, electrical current from the live internal wire shorts to ground and a fire or overheat indication is generated.
Dual loop systems provide two important benefits:
Dual loop systems minimize the possibility of false fire warnings. Both loops must sense the fire or overheat condition under exacting parameters before flight deck fire indications are generated.
Dual loops provide greater dispatch capability as the aircraft can be dispatched with a faulted loop and still maintain fire and overheat protection.
Engine Fire Extinguisher Bottles
The fire bottles, containing the extinguishing agent Halon, are installed in the aft equipment. A pressure gauge and two explosive squibs, each one with two firing bridgewires fed by separate electrical circuits, are installed on each fire bottle.
If required, both bottles can be discharged into one engine. The selection of the LH or RH FIRE PUSH switchlight will determine the order in which the squibs are fired.
LH (RH) FIRE PUSH Switchlights
The engine fire extinguishing system is controlled by the LH (RH) FIRE PUSH switchlights.
When the LH or RH FIRE PUSH switchlight is pressed:
• the bottles squibs are armed, both BOTTLE ARMED PUSH TO DISCH switchlights illuminate
• the fuel feed shutoff valve (SOV) closes
• bleed air shutoff valve (SOV) closes
• hydraulic shutoff valve (SOV) closes
• engine driven generator is tripped off
BOTTLE ARMED PUSH TO DISCH Switchlights
When the BOTTLE ARMED PUSH TO DISCH switchlight is pressed, electrical current fires the squib in the associated bottle and pressurized Halon is directed into the affected engine nacelle. The selection of the LH or RH FIRE PUSH switchlight will determine into which engine nacelle the bottles will be discharged.
Auxiliary Power Unit Fire Protection
The auxiliary power unit (APU) dual loop fire detection system detects a fire or overheat condition within the APU enclosure. The fire detection system continuously monitors the APU.
It has two modes of operation:
On the ground, when a fire condition is detected, the APU shuts down automatically. Five seconds later, the APU fire bottle automatically discharges Halon into the APU enclosure.
In flight, when a fire condition is detected, the APU shuts down automatically. The flight crew must discharge the bottle.
The fire extinguishing system consists of a fire extinguisher bottle with an explosive squib and two firing bridgewires. The extinguishing agent, Halon, is discharged into the APU enclosure.
APU Fire Extinguishing Bottle
The fire extinguisher bottle is filled with Halon and is equipped with a pressure gauge and one explosive squib with two firing bridgewires. The fire bottle is installed in the aft equipment bay.
APU FIRE PUSH Switchlight
the bottle squib is armed and the BOTTLE ARMED PUSH TO DISCH switchlight illuminates
• APU fuel feed shutoff valve closes
• APU fire shutoff relay is energized to shutdown the APU by closing the fuel solenoid valve
• APU LCV closes
• APU generator is tripped off
Fire and Protection
The fire protection system is divided into two separate sub-systems:
• fire and overheat detection system
• fire extinguishing system.
The fire and overheat detection system include components which detect fire, overheat, or smoke conditions.
The fire extinguishing system includes the containment and delivery of an extinguishing agent to all protected areas of the aircraft.
The detection and extinguishing systems can be tested and monitored from the flight deck.
The Fire Protection System, Smoke Detection Systems and Fire Extinguishing Systems for the engines, the APU and the cargo bays are connected to the fire detection and extinguishing (FIDEEX) unit.
Fire detection control unit
The FIDEEX unit is used to monitor the electrical resistance of the loops. When both loops experience the same decrease in resistance in a preset time, the unit sends a FIRE/OVHT signal to the EICAS. The FIDEEX unit is capable of discriminating between a real fire and a false fire. Each individual control circuit and its related sensing loop is monitored so that in the event of a malfunction of one loop, the second loop maintains the capability of detecting a fire.
Cargo bay fire protection
A smoke detection system in each cargo bay protects the aircraft and its passengers from a cargo bay fire.
Three smoke detectors are installed in the forward cargo bay and two in the aft cargo bay. Two firex bottles are installed in the right wing fairing. A control panel is installed on the center pedestal. The system is connected to the FIDEEX unit and tested with the switch on the FIRE DETECTION / FIREX MONITOR test panel.
Cargo smoke detectors
The forward cargo bay has three smoke detectors installed on the ceiling while the aft cargo bay has two. The smoke detectors monitor the cargo bay for the presence of smoke. When smoke is detected, an AFT or FWD CARGO SMOKE warning message is presented on EICAS primary page, the AFT or FWD CARGO SMOKE PUSH switchlight on the CARGO FIREX panel illuminates and a triple chime followed by the aural warning ‘SMOKE’ are heard.
NOTE
Operation of mobile transceivers in close proximity to the smoke detectors or exhaust fumes from ground handling equipment may cause a false alarm.
Pressing the affected FWD or AFT CARGO SMOKE PUSH switchlight
selects the bay where the fire extinguishing agent will be discharged. It also arms the fire extinguishers and causes the illumination of the single BOTTLE ARMED PUSH TO DISH green switchlight. In addition, pushing the AFT CARGO SMOKE PUSH switchlight shuts off the cargo bay heater and closes the air conditioning shut-off valve (SOV) in the aft baggage compartment.
Cargo Fire Extinguishing Bottles
The bottles are located in the right wing fairing are filled with Halon. Each bottle is equipped with a pressure gauge and two squibs. Each squib is fired by dual bridgewires fed by different electrical circuits. The fire bottles discharge the Halon at different rates. Both bottles are fired at the same time but only bottle No.1 discharges immediately. Bottle No.2 discharges its contents slowly to maintain Halon concentration in the cargo bay for an extended period of time and prevent the reigniting of a smoldering fire.
