15.20 Fire Protection Systems Flashcards
What is the primary threat to all aircraft?
Fire
Fire is considered the most dangerous threat to aircraft, necessitating fire protection systems.
What is a ‘fire zone’ in aircraft?
An area designated by the manufacturer that requires fire detection and/or extinguishing equipment and high fire resistance.
Which aircraft components must have fire protection systems?
Multi-engine turbine-powered aircraft and Auxiliary Power Units (APUs).
What are the two major types of turbine failure?
- Thermodynamic
- Mechanical
What causes thermodynamic turbine failure?
An upset in the proportion of air used to cool combustion temperatures.
What can result from severe overheating in turbines?
Melting of turbine blades and loss of thrust.
What is a potential risk associated with mechanical turbine failure?
Fractured or thrown blades puncturing the tail cone and causing overheating or fires.
What are the components of a complete fire protection system?
Fire detection and fire extinguishing systems.
Which types of detectors are used to detect fires in aircraft?
- Overheat detectors
- Rate of temperature rise detectors
- Flame detectors
What features should a fire detector system include?
- No false warnings
- Rapid indication of fire
- Accurate location of fire
- Indication that fire is out
- Indication of reignited fire
- Continuous indication during a fire
- Electrically testable from the flight deck
- Damage resistance
- Lightweight and easy to mount
- Operable from aircraft power system
- Minimum current requirements
What types of fire detection systems are commonly installed in aircraft?
- Spot detectors
- Continuous loop systems
What is a thermal switch system?
A fire detection system comprising heat-sensitive units that complete electrical circuits at a set temperature.
How does a thermocouple fire warning system operate?
It produces voltage based on temperature differences between the reference and hot junctions.
What is the function of infrared optical fire detectors?
To detect specific radiation emissions from hydrocarbon flames.
What principle does the pneumatic thermal fire detection system operate on?
Gas laws, utilizing a closed helium-filled tube.
What temperature range does the average temperature sensing function activate in pneumatic detectors?
93 °C (200 °F) to 371 °C (700 °F).
What is the purpose of the titanium wire in the pneumatic continuous system?
To release hydrogen gas when exposed to a heat source, triggering the warning system.
What are the two widely used types of continuous loop systems?
- Fenwal systems
- Kidde systems
How does the Fenwal continuous loop system detect a fire?
By monitoring the resistance drop of eutectic salt when overheated.
What happens when the temperature of the core in a Kidde continuous loop system increases?
Electrical resistance decreases, leading to a fire warning indication.
What is the advantage of the sensing element in a continuous loop system?
It reflects an average resistance, allowing for sensitivity to overheating without false alarms.
What type of warning does the analogue signal from the thermistor sensing element provide?
A two-level response indicating both overheat and fire conditions.
What is the purpose of the alarm point in fire detection systems?
To be set close to the maximum general ambient temperature for greater sensitivity to overheat or fire without false alarms from localized hot spots.
What are the two levels of response in a combination fire and overheat warning system?
- Overheat warning below fire warning level
- Fire warning above overheat level
What does the temperature trend indication in fire detection systems provide?
It indicates engine compartment temperature increases from normal and checks the condition of the fire detection system.
How can the integrity of the continuous loop fire detection system be tested?
By actuating a test switch in the flight deck that simulates the sensing element resistance change due to fire.
What does the fault indication provision do in the fire detection control unit?
Sends a fault signal to activate a fault indicator if a short in the sensing element loop is detected.
What logic arrangement do dual loop systems use for better reliability?
‘AND’ logic, requiring both loops to signal for a fire warning.
What happens if one loop of a dual loop system becomes defective in flight?
The flight deck fault signal alerts the crew to select single loop operation.
What is the role of automatic self-interrogation in dual loop systems?
It eliminates fault indication and assures immediate detection of fire indication if a fire occurs.
What does the fire detection control unit typically contain?
Electronic resistance monitoring and alarm output circuits housed in a hermetically sealed case.
What are the designated fire zones in a powerplant installation?
- Engine power section
- Engine accessory section
- APU compartment
- Fuel-burning heater installations
- Compressor and accessory sections of turbine engines
- Combustor, turbine, and tailpipe sections
What is required for transport category certified aircraft regarding fire extinguishing systems?
Two discharges producing a sufficient concentration of extinguishing agent.
What is the most common extinguishing agent used in engine fire protection systems?
Halon 1301.
What materials can be used for fire extinguisher containers?
- Stainless steel
- Titanium
What is the function of the temperature/pressure-sensitive safety relief diaphragm in fire extinguisher containers?
Prevents container pressure from exceeding test pressure in excessive temperatures.
What are the two types of cartridge disk release techniques for discharge valves?
- Standard release type
- High-temperature or hermetically sealed unit type
What type of fire extinguisher pressure indication system is commonly used?
A combination gauge switch that visually indicates actual container pressure.
What is the purpose of two-way check valves in a two-shot system?
To prevent agent backup from the reserve container into the previously emptied main container.
What does the thermal discharge indicator show?
Ejects a red disc when container contents have been dumped due to excessive heat.
What happens when a fire switch is activated in the flight deck?
- Engine stops
- Fire extinguishing system is armed
What warning systems are installed in the flight deck for engine fire detection?
- Horn sounds
- Warning lights illuminate
What indications occur in the flight deck if an engine fire is detected?
- Master warning lights come on
- Fire warning aural operates
- Engine fire warning message shows
