Engine Fire Protection Systems

Question 1

What are the four types of engine fire detection systems?

Answer 1

1. Thermoswitch system
2. Thermocouple system
3. Thermistor-type continuous-loop system
4. Pneumatic-type continuous-loop system

Question 2

Which type of fire detection system operates on the principle of the rate of temperature rise

Answer 2

The thermocouple system

Question 3

Why must the reference junction in a thermocouple fire detection system be thermally insulated?

Answer 3

This is a rate-of-temperature-rise system. The reference junction must be insulated so its temperature will not rise as quickly as that of the measuring junctions if a fire should occur

Question 4

How do you check a thermocouple fire detection system for operation?

Answer 4

Press the test switch. This heats the test thermocouple enough for it to close the sensitive relay, which in turn closes the slave relay and activates the fire warning light and bell

Question 5

How is a pneumatic-type continuous-loop fire detection system checked for operation?

Answer 5

When the test switch is closed, low-voltage AC flows through the tube that encloses the sensitive element. This current heats the element enough for it to release sufficient gas to activate the alarm switch

Question 6

What group of fire extinguishing agents are no longer manufactured because of environmental concerns?

Answer 6

Halons (or freon or chlorofluorocarbons [CFCs] were no longer manufactured after 1995. However existing stocks of CFC may still be used and are subject to strict handling and disposal regulations.

Question 7

How are fire extinguishing agents distributed?

Answer 7

Through perforated tubing and/or discharge nozzles.

Question 8

What is the purpose of the discharge cartridge and how is it activated?

Answer 8

The discharge cartridge, or squib, which is electrically ignited, fires a projectile into the frangible disk, which releases the fire extinguishing agent.

Question 9

How is a fire extinguisher system with a high rate of discharge classified?

Answer 9

As an HRD fire extinguisher system.

Question 10

What do the red and yellow discs in a fire extinguishing system indicate?

Answer 10

A yellow disc indicates a normal discharge. A red disc indicates thermal discharge.

Question 11

How is the fire extinguishing agent in an HRD system distributed, and how long does it take to discharge?

Answer 11

The agent is distributed through a series of high pressure tubes and takes one to two seconds to discharge.

Question 12

What is the purpose of a pressure gauge in a fire extinguishing system?

Answer 12

Indicates pressure within the container. To check if the pressure is within limits, a pressure-temperature chart is used.

Question 13

What types of fire detector systems are used for engine fire detection?

Answer 13

Overheat, rate of rise, and flame detectors.

Question 14

How does a thermal switch fire protection system operate?

Answer 14

When heated past a predetermined temperature, the switch closes causing the warning devices in the cockpit to activate.

Question 15

How many thermal switches are needed in a thermal switch fire protection system?

Answer 15

At least one.

Question 16

What kind of fire detection system allows for more complete coverage than a spot-type system?

Answer 16

A continuous loop system.

Question 17

What happens if an engine equipped with a thermocouple fire warning system overheats slowly?

Answer 17

Nothing, because a fast temperature rise or rapid heating is required for this type of fire system to operate.

Question 18

What electrical power is required for a thermocouple fire protection system to operate?

Answer 18

Both the thermocouple-produced power and the aircraft electrical system are required for this type of fire protection system to operate.

Question 19

What is the likely cause of a false fire warning?

Answer 19

The engine fire sensing loop is bent or kinked excessively.

Question 20

What are the fire extinguishing systems designed to do?

Answer 20

They are designed to dilute the oxygen levels around the engine to a point that does not allow combustion, or to reduce temperatures below the ignition point.

Question 21

Describe how a Kidde and Fenwal continuous loop fire protection system functions.

NO

Answer 21

A Kidde system has a sensing element consisting of a sealed inconel tube containing two conductors that are embedded in a thermistor material. One wire is electrically grounded, and the other is a positive lead. When a fire or overheat occurs, the resistance of the thermistor material drops, allowing current to flow between the two wires to activate an alarm. A Fenwal system uses a sensing element consisting of a small diameter flexible inconel tube containing a single wire electrode surrounded by ceramic beads. These ceramic beads prevent the electrode and tube from touching each other. Current is applied to the electrode while the outer tube is grounded to the aircraft structure. When a fire or overheat occurs, the core resistance of the ceramic beads drops, allowing current to flow between the center electrode and ground, energizing the alarm system.

Question 22

What elements must be present for a fire to occur?

Answer 22

An ignition source such as heat or a spark, fuel and oxygen.