Reworked Unit 2 Review

What three items does a fire need to continue to burn?

Fuel

Oxygen

Heat

What is a Class A fire made up of?

Class A – Wood, Paper, Cloth

What is a Class B fire made up of?

Class B – Combustible liquids, Gas, Paint Thinner

What is a Class C fire made up of?

Class C – Energized electrical equipment

What is a Class D fire made up of?

Class D – Burning Metal - Magnesium

What is Fire Zone A?

A – Large quantities of airflow passing arrangements of similarly shaped obstructions (recip engine)

What is Fire Zone B?

B – Large quantities of airflow past aerodynamically clean obstructions (heat exchange ducts)

What is Fire Zone C?

C - Relatively low airflow (APU Compartment)

What is Fire Zone D?

D- Little or no airflow – (Wing Compartments, wheel wells)

What is Fire Zone X?

X – Have large airflow and are of unusual construction, typically requires twice the amount of extinguishing agent used in Zone A

What physical properties can fire detection systems measure? (List 3)

Temperature

Smoke

Flame

How are Fenwal thermal switches constructed?

Is a spot detection system that uses a number of thermally activated switches.

The switch is mounted in a stainless steel housing – when it heats up, it elongates causing the switch to close.

Typically not adjustable in the field.

In a spot type detector system with multiple switches and one warning light, how is the detector system wired?

Spot type fire detector systems in aviation are wired in parallel to enhance safety and reliability

This design allows for a single fault in one circuit to not trigger a false alarm, ensuring that the system remains trustworthy and does not alarm the crew unnecessarily. The parallel wiring setup is a design choice that prioritizes safety and reliability, preventing unnecessary panic and ensuring effective fire detection

What design criteria must a fire detection system meet? (List 9)

1. Prevents false warnings

2. Rapid indication of a fire and accurate indication of location

3. Must have an accurate indication that the fire has been extinguished

4. Automatically reset

5. Continuous indication

6. Must be able to test from cockpit

7. Resist exposure to oil, water, vibrations, temperature

8. Must have a cockpit light and audible alarm

9. Separate sensing for each engine

A Class D fire is dangerous because?

The metal burns so hot that using normal extinguishing agents pose a hazard to the people using them.

What is the benefit of a double loop thermal switch system compared to a single loop thermal switch detector system?

With this design the circuit can withstand one fault (short or open circuit)

Redundancy

Which detector system is considered a temperature rate of rise detector system?

Thermocouple system

Where are active thermocouples located?

Active thermocouples are placed are placed in fire zones around an engine.

A thermocouple consists of a loop of two dissimilar metal wires (chromal, constantan) that are joined at each end to form two junctions. When a temperature difference exists between the two junctions electrical current flows and activates a warning light.

Where is the reference thermocouple located?

The reference thermocouple is placed in a dead air space between two insulated blocks.

Under normal operation the temp around the reference thermocouple and active thermocouples are relatively even, and no current is produced to activate a light.

When fire occurs the air temperature around the active thermocouples rise much faster than the reference thermocouple, this difference produces a current that activates the fire warning.

What type of detector has two wires in a thermistor material inside of an inconel tube?

Kidde

How are continuous loop systems installed to ensure redundancy?

Using a dual loop system

Which detector incorporates an integrity switch in the system?

Systron-Donner

What will cause the integrity switch to open?

If your helium gas escapes, the pressure drop will allow the switch to open.

What material changes its resistance when heat is applied in the Fenwal detector?

Eutectic Salt

What category of fire detectors will be used in Class C and D fire zones?

Continuous Loop

• APU enclosures are Class C

• Wheel wells are Class D

What is the purpose of the titanium wire inside the Systron-Donner pneumatic system?

Acts as a gas-absorption material and contains a quantity of hydrogen

What system has a history of false alarms when flying over water at night?

Infrared flame detector systems have historically been prone to false fire warnings during night operations or when flying over water due to IR light reflections

Reflected IR energy from:

• Sunlight or moonlight

• Water surfaces (especially calm water)

• Clouds or atmospheric conditions at night can be misinterpreted as a fire.

• Improper installation angles make this worse, allowing unintended light sources to enter the sensor field of view

What is the cause of most false fire warnings in a continuous loop detector system?

Caused by a short circuit due to sharp bends, kinks, loose wires.

Smoke detectors that measure the amount of light transmissibility in the air are called?

Light refraction type

Which type of fire extinguisher will automatically discharge in the event of a fire?

Lavatory trash compartments have automatic extinguishers where solder melts releasing the agent.

What does a carbon dioxide extinguisher have to have before it can be used on an electrical fire?

The extinguisher has a nonmetallic discharge horn

How does carbon dioxide extinguish fire?

Displaces oxygen and interrupts the chemical reaction between the fuel and the oxygen.

Which extinguishing agents are the least toxic?

Bromotrifluoromethane (Halon 1301)

Why do conventional extinguishing systems need strong but heavy containers?

Because of C02 variation in vapor pressure with temperature it is required to store CO2 in stronger, heavier containers.

A conventional system uses CO2.

How is a CO2 fire extinguishers stabilized for use in extreme temperatures?

They are charged with about 200 psi of dry nitrogen before they are charged with CO2.

This is done to prevent thermal discharge in hot temperatures and to add pressure to help the release of the Carbon Dioxide.

What is the only way to determine if the proper amount of extinguishing agent is in an extinguisher?

By weighing the bottle

In a HRD bottle what holds the nitrogen and extinguishing agent in the bottle?

Sealed with a frangible disk

Contains a bonnet assembly (operating head) that contains an electrically charged discharge cartridge (squib) which fires a projectile into the frangible disk.

HRD bottles have a thermal fuse that melts and releases the agent if the bottle is exposed to high temperatures – the bottle will discharge into the atmosphere and this will be indicated by a red indicator disc

What is a squib and what is its function in a HRD bottle?

An electrically ignited discharge cartridge.

A strainer is installed in the bonnet assembly to prevent broken disc fragments for getting into the line.

When the squib is activated it hits the frangible disc and this is a normal discharge of the extinguishing agent.

A yellow indicator discs blows out to show a normal discharge.

What do mechanics have to inspect HRD bottle squibs for?

The service life is calculated from the manufacturers date stamped on the cartridge.

Squibs are a life limited unit.

Where can you find the manufacture date of the squib?

Stamped on the cartridge

On the side of the fuselage outside of conventional and HRD extinguisher bottles there are two colored discs, what are the colors and what does each color mean?

Red – thermal discharge

Yellow – Normal discharge

How is one HRD fire extinguisher used to protect multiple areas?

By being equipped with two discharge bonnets and two discharge ports

What is the purpose of the screen in the HRD bottle bonnet?

To catch the disc fragments so they don’t get into the distribution lines

Where is the hydrostatic test date stamped on an HRD bottle?

The date is permanently stamped into the metal of the fire extinguisher bottle, not painted or labeled.

It is usually found on the neck or shoulder adjacent to the valve.

The stamp typically includes: Month and year of the hydrostatic test

Sometimes the test facility’s ID or symbol

How is the safety and performance of an extinguisher’s pressure vessel ensured?

By hydrostatic testing

Hydrostatic testing is a pressure check of a high pressure container to determine container strength.

Is water is an effective extinguishing agent for a class B fire?

Flammable liquids are lighter than water and do not mix with it.

When water is applied, it sinks below the fuel, causing the burning liquid to float and spread to a larger area

How is a CO2 fire extinguishers stabilized for use in extreme temperatures?

• They are charged with about 200 psi of dry nitrogen before they are charged with CO2

• This is done to prevent thermal discharge in hot temperatures and to add pressure to help the release of the Carbon Dioxide.

What two locations are smoke detectors commonly used in aircraft?

Lavatory

Cargo

What is the function of a fire detection system?

To provide a continuous indication when a fire exists

Which of the following is the operating principle of a spot detector sensor in a fire detection system?

A bimetallic thermoswitch that closes when heated to a high temperature.

A fire detection system that uses a single wire surrounded by a continuous string of ceramic beads in a tube is the

Fenwall System

How do you properly ground a squib to prevent accidental firing?

Wrapping a piece of safety wire between the two electrical terminals of the discharge cartridge is sometimes done to keep both terminals electrically neutral.

No voltage difference across the squib with the terminals tied together, both ends of the squib are at the same electrical potential.

Without a voltage difference, no current flows through the bridge wire.

Static charges are harmlessly bled off to ground instead of passing through the squib.

What is this and what is the wire?

A Squib

A grounding wire, shorting wire, safety wire

What factors are taking into account when determining aircraft fire zones?

The amount of air flow through the space

The size, shape and number of obstructions.

IR and UV flame detectors can provide false indication if they're not installed correct or if unwanted light enters.

a. True

b. False

a. True

The explosive charge (squib) in the bonnet of a fire extinguisher container is...

A life limited unit

The fire detection system that uses two wires embedded in a thermister core within a tube is the...

Kidde system

A Class D fire is dangerous because the metal burns so hot that using normal extinguishing agents pose a hazard.

a. True

b. False

a. True

A Carbon Dioxide fire extinguisher can be used on an electrical fire if...

The extinguisher has a nonmetallic discharge horn

Which of the following is a principle of operation of a continuous-loop fire detector system sensor?

Core resistance material which prevents current flow at normal temperatures

What is the function of a fire detection system?

To provide a continuous indication when a fire exists

A continuous loop fire detector will pass the self-test even if one of the two loops are inoperative.

a. true

b. false

b. false

Which detector system uses an integrity switch to ensure detector condition?

c. Systron Donner detection system

Which fire detection systems measures temperature rise compared to a reference?

Thermocouple

The most common cause of false fire warnings in continuous-loop fire-detection systems is...

Dents, kinks, or crushed sensor sections

What is Hydrostatic testing?

Pressure check of a high pressure container to determine container strength

When used in fire-detection systems having a single indicator light, thermal switches are wired in...

Parallel with each other and in series with the light

A fire detection system that uses a single wire surrounded by a continuous string of ceramic beads in a tube is the...

Fenwall system

What is the operating principle of a spot detector sensor in a fire detection system?

A bimetallic thermoswitch that closes when heated to high temperature

The titanium hydride core of a Systron Donner continuous loop system will conduct electricity when heated.

a. True

b. False

b. False

How does carbon dioxide (CO2) extinguish an aircraft engine fire?

The CO2 displaces the oxygen, removing one element hat fire requires

Which fire-extinguishing agent is considered to be the least toxic?

d. Bromotrifluoromethane (Halon 1301)

Why are Carbon Dioxide extinguisher bottles charged with dry nitrogen?

To prevent thermal discharge in hot temperatures and to add pressure

HRD fire extinguisher bottle can be used for multiple areas, is it possible to connect the wiring to the wrong squib.

a. True

b. False

a. True

Water is an effective extinguishing agent for a class B fire because the water will absorb the heat of the fire.

a. True

b. False

b. False

Smoke detectors which use a measurement of light transmissibility in the air are called...

Photoelectric (Optical).

Light Refraction Type is one of them.