Aircraft fire protection systems

Question 1

What are the principles of extinguishing fires?

Answer 1

• Cool the fuel below its ignition point
• Remove the oxygen supply
• Separate the fuel from the oxygen

Question 2

What are class A extinguishing agents?

Answer 2

Responds best to water or water type which lower the fuel below its ignition point

Question 3

What are class B extinguishing agents?

Answer 3

Responds to carbon dioxide, halogenated hydrocarbons, and dry chemicals, all which displace the oxygen supply making combustion impossible.

• Dry powder
• Halo
• CO2

Question 4

What are class C extinguishing agents?

Answer 4

• Respond best to CO2 which displaces the oxygen
• Must have a non-mettalic horn to prevent static electricity and transmission of electricity to operator from the electrical source.
• Halons or dry chemicals can be used but this could lead to further contamination and damage of electrical systems.

Question 5

What are class D extinguishing agents?

Answer 5

Responds best to dry powder which prevents oxidation and the resulting flame.

Question 6

Where are aircraft required to have protection systems?

Answer 6

In designated fire zones and potential fire zones

Question 7

Smoke detection and Gas detection principles?

Answer 7

• Used for anticipating a fire that produces smoke before significant temperature changes
• Typically in cargo/baggage and lavatories
• Light refraction type (photoelectric cell)
• Ionisation type
• Solid-state type

Question 8

Types of fire/overheat detection systems?

Answer 8

Thermo switch
thermocouple
Tubular type
- Fenwal
- Kidde
 -Pneumatic type

Question 9

Explain the thermo switch system?

Answer 9

• A circuit where one or more thermal switches are connected in parallel, and then to a warning horn and an aural alarm system
• (spot detector) works by the expansion of the outer casing unit
• When exposed to heat the casing becomes longer, causing the two contacts inside to meet closing the circuit
• Closing the circuit activates the warning system on the flight deck.

Question 10

Explain the thermocouple system?

Answer 10

• Rate of the rise detection system
• A circuit where one or more thermocouples are connected in series to activate an alarm when there is a sufficient temperature increase at the sensor
• Thermocouples made of two dissimilar metals which are twisted together inside an open frame
• Allows for flow through the probe not allowing damage to the wires.

Question 11

Explain the fenwall system?

Answer 11

• Continous loop system
• Consists of a small lightweight, flexible Inconel tube with pure nickel wire conductor running throughe middle
• The space between the nickel conductor and tubing wall is filled with porous aluminum oxide, ceramic insulating material
• Any voids or clearances are saturated with a eutectic salt mixture which has a low melting point
• Tube is hermetically sealed at both ends, with insulating materials and threaded fittings.

Question 12

How does the fenwall system detect heat?

Answer 12

• When heated, current can flow between the centre wire and the tube wall because the eutectic salts melt, and the resistance drops rapidly.
• The increased current flow provides a signal. which is used in the control unit to sound an alarm.
• Once the fire is extinguished or overheat condition is corrected eutectic salt increases its resistance and the system returns to stand by mode.

Question 13

Explain the kiddie system?

Answer 13

• Continous loop system
• Uses an Inconel tube with a thermiresistor material embedded with two electrical conductors (which helps to prevent redundancy)
• One conductor is grounded to the outer shell at the end of the tube

Question 14

How does the kiddie system detect heat?

Answer 14

• When heated the thermistor material drops in resistance

Question 15

Explain the Pneumatic System?

Answer 15

• Continous length system
• Sensing element consists of a stainless steel tube containing two separate gases plus a gas absorption material in the form of a wire in the tube.
• Tube under pressure and filled with helium gas
• The titanium wire centre, which is a gas absorption material, contains hydrogen gas.
• Wire wrapped in helical fashion with inert metal tape for stabilization
• Gaps between the turns of tape allow for rapid release of hydrogen gas from the wire when the temperature reaches the required level

Question 16

How does the pneumatic system detect heat?

Answer 16

• If the volume is constant, its pressure will increase with temperature
• The helium gas exerts a pressure that closes the pneumatic switch which operates the warning system.
• After the situation is corrected the titanium reabsorbs the hydrogen and the system returns to stand by mode

Question 17

What are conventional fire extinguishing systems?

Answer 17

• Used on older aircraft

- Utilizes Co2

Question 18

What are high rate discharge fire extinguishing systems?

Answer 18

• Used widely and more efficient then conventional
• Utilizes freon or halon 1301
• Uses N2 to propel the extinguishing agent at higher speeds.
• Uses spherical bottles under high pressure actuated by explosive charge to flow the compartment and displace oxygen

Question 19

Operation of a high rate discharge extinguishing system?

Answer 19

• fire switch was closed by a crew member in the area where a fire is indicated
• Explosive charge at the neck of the bottle is detonated and a cutter is driven through the sealing disk in the enck
• Instantly release extinguishing agent to the area selected.

Question 20

What does a yellow displaced disk indicate?

Answer 20

Bottle cartridge has fired

Question 21

What does a red disk indicate?

Answer 21

Discharge through over heat and over pressure.