Chapter 11 Engine Fire Protection

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

Overheat, rate of rise, and flame detectors.

How does a thermal switch fire protection system operate?

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

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

At least one.

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

A continuous loop system.

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

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

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

Both the thermocouple-produced power and the aircraft electrical system are required.

What is the likely cause of a false fire warning?

The engine fire sensing loop is bent or kinked excessively.

What are fire extinguishing systems designed to do?

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.

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

A Kidde system has a sensing element consisting of a sealed Inconel tube containing two conductors embedded in thermistor material. A Fenwal system uses a small diameter flexible Inconel tube with a single wire electrode surrounded by ceramic beads.

What elements must be present for a fire to occur?

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

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

Halons (or Freon or chlorofluorocarbons [CFCs]) were no longer manufactured after 1995.

How are fire extinguishing agents distributed?

Through perforated tubing and/or discharge nozzles.

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

The discharge cartridge, or squib, is electrically ignited to fire a projectile into the frangible disk, releasing the fire extinguishing agent.

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

As an HRD fire extinguisher system.

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

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

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

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

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

Indicates pressure within the container and checks if the pressure is within limits using a pressure-temperature chart.