15.20 Fire Protection Systems

Question 1

What is the primary threat to all aircraft?

Answer 1

Fire

Fire is considered the most dangerous threat to aircraft, necessitating fire protection systems.

Question 2

What is a ‘fire zone’ in aircraft?

Answer 2

An area designated by the manufacturer that requires fire detection and/or extinguishing equipment and high fire resistance.

Question 3

Which aircraft components must have fire protection systems?

Answer 3

Multi-engine turbine-powered aircraft and Auxiliary Power Units (APUs).

Question 4

What are the two major types of turbine failure?

Answer 4

• Thermodynamic
• Mechanical

Question 5

What causes thermodynamic turbine failure?

Answer 5

An upset in the proportion of air used to cool combustion temperatures.

Question 6

What can result from severe overheating in turbines?

Answer 6

Melting of turbine blades and loss of thrust.

Question 7

What is a potential risk associated with mechanical turbine failure?

Answer 7

Fractured or thrown blades puncturing the tail cone and causing overheating or fires.

Question 8

What are the components of a complete fire protection system?

Answer 8

Fire detection and fire extinguishing systems.

Question 9

Which types of detectors are used to detect fires in aircraft?

Answer 9

• Overheat detectors
• Rate of temperature rise detectors
• Flame detectors

Question 10

What features should a fire detector system include?

Answer 10

• 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

Question 11

What types of fire detection systems are commonly installed in aircraft?

Answer 11

• Spot detectors
• Continuous loop systems

Question 12

What is a thermal switch system?

Answer 12

A fire detection system comprising heat-sensitive units that complete electrical circuits at a set temperature.

Question 13

How does a thermocouple fire warning system operate?

Answer 13

It produces voltage based on temperature differences between the reference and hot junctions.

Question 14

What is the function of infrared optical fire detectors?

Answer 14

To detect specific radiation emissions from hydrocarbon flames.

Question 15

What principle does the pneumatic thermal fire detection system operate on?

Answer 15

Gas laws, utilizing a closed helium-filled tube.

Question 16

What temperature range does the average temperature sensing function activate in pneumatic detectors?

Answer 16

93 °C (200 °F) to 371 °C (700 °F).

Question 17

What is the purpose of the titanium wire in the pneumatic continuous system?

Answer 17

To release hydrogen gas when exposed to a heat source, triggering the warning system.

Question 18

What are the two widely used types of continuous loop systems?

Answer 18

• Fenwal systems
• Kidde systems

Question 19

How does the Fenwal continuous loop system detect a fire?

Answer 19

By monitoring the resistance drop of eutectic salt when overheated.

Question 20

What happens when the temperature of the core in a Kidde continuous loop system increases?

Answer 20

Electrical resistance decreases, leading to a fire warning indication.

Question 21

What is the advantage of the sensing element in a continuous loop system?

Answer 21

It reflects an average resistance, allowing for sensitivity to overheating without false alarms.

Question 22

What type of warning does the analogue signal from the thermistor sensing element provide?

Answer 22

A two-level response indicating both overheat and fire conditions.

Question 23

What is the purpose of the alarm point in fire detection systems?

Answer 23

To be set close to the maximum general ambient temperature for greater sensitivity to overheat or fire without false alarms from localized hot spots.

Question 24

What are the two levels of response in a combination fire and overheat warning system?

Answer 24

• Overheat warning below fire warning level
• Fire warning above overheat level

Question 25

What does the temperature trend indication in fire detection systems provide?

Answer 25

It indicates engine compartment temperature increases from normal and checks the condition of the fire detection system.

Question 26

How can the integrity of the continuous loop fire detection system be tested?

Answer 26

By actuating a test switch in the flight deck that simulates the sensing element resistance change due to fire.

Question 27

What does the fault indication provision do in the fire detection control unit?

Answer 27

Sends a fault signal to activate a fault indicator if a short in the sensing element loop is detected.

Question 28

What logic arrangement do dual loop systems use for better reliability?

Answer 28

'AND' logic, requiring both loops to signal for a fire warning.

Question 29

What happens if one loop of a dual loop system becomes defective in flight?

Answer 29

The flight deck fault signal alerts the crew to select single loop operation.

Question 30

What is the role of automatic self-interrogation in dual loop systems?

Answer 30

It eliminates fault indication and assures immediate detection of fire indication if a fire occurs.

Question 31

What does the fire detection control unit typically contain?

Answer 31

Electronic resistance monitoring and alarm output circuits housed in a hermetically sealed case.

Question 32

What are the designated fire zones in a powerplant installation?

Answer 32

* Engine power section * Engine accessory section * APU compartment * Fuel-burning heater installations * Compressor and accessory sections of turbine engines * Combustor, turbine, and tailpipe sections

Question 33

What is required for transport category certified aircraft regarding fire extinguishing systems?

Answer 33

Two discharges producing a sufficient concentration of extinguishing agent.

Question 34

What is the most common extinguishing agent used in engine fire protection systems?

Answer 34

Halon 1301.

Question 35

What materials can be used for fire extinguisher containers?

Answer 35

* Stainless steel * Titanium

Question 36

What is the function of the temperature/pressure-sensitive safety relief diaphragm in fire extinguisher containers?

Answer 36

Prevents container pressure from exceeding test pressure in excessive temperatures.

Question 37

What are the two types of cartridge disk release techniques for discharge valves?

Answer 37

* Standard release type * High-temperature or hermetically sealed unit type

Question 38

What type of fire extinguisher pressure indication system is commonly used?

Answer 38

A combination gauge switch that visually indicates actual container pressure.

Question 39

What is the purpose of two-way check valves in a two-shot system?

Answer 39

To prevent agent backup from the reserve container into the previously emptied main container.

Question 40

What does the thermal discharge indicator show?

Answer 40

Ejects a red disc when container contents have been dumped due to excessive heat.

Question 41

What happens when a fire switch is activated in the flight deck?

Answer 41

* Engine stops * Fire extinguishing system is armed

Question 42

What warning systems are installed in the flight deck for engine fire detection?

Answer 42

* Horn sounds * Warning lights illuminate

Question 43

What indications occur in the flight deck if an engine fire is detected?

Answer 43

* Master warning lights come on * Fire warning aural operates * Engine fire warning message shows