15:20 Fire Protection Systems

Question 1

Fire detection systems are always installed in areas where technical failure or human error are most likely to produce a fire. Where are these areas

Answer 1

Engine and APU areas

Question 2

All fire detection systems contain what 3 main components

Answer 2

• A sensor located in the monitored area
• A control unit, primarily located in the avionics compartment which receives the signals from the sensor
• Warning panels, which are mostly located in the cockpit

Question 3

Other than detecting fires what do the detection sensors also detect

Answer 3

They are used for overheat detection

Question 4

The fire detection system finds a fire by detecting what?

Answer 4

The heat of the fire

Question 5

What does the spot sensor use to detect fires

Answer 5

Usually a bi-metallic switch

Question 6

How does a bi-metallic switch work

Answer 6

It triggers an alarm when it closes due to the heat

This type of sensor is used for pneumatic ducts because many individual sensors are needed for larger areas and because defective sensors are hard to detect

Question 7

What are continuous loop sensors usually used on

Answer 7

Engines

Question 8

What are the two different types of continuous loops

Answer 8

• The semiconductor loop
• The pneumatic pressure loop

They look almost identical but work differently

Question 9

What is the pneumatic pressure loop called

Answer 9

A Systron-and Donner loop after the manufacturer

Question 10

How does the pneumatic pressure loop work

Answer 10

It consists of a steel tube which contains gas. When the pressure in the tube increases due to higher temperature it operates a pressure switch which, when closed, triggers the alarm via the control unit

This switch is located in the thicker end of the loop and is called the RESPONDER

Question 11

What are the other names of semiconductor called after their manufacturers

Answer 11

Kidde, Graviner, Edison or Fenwal

Question 12

How does a semiconductor loop work

Answer 12

Each loop has a metal tube that contains a semiconductor material. This material decreases its electrical resistance with increasing temperature. An alarm is triggered when the resistance between the central wire and the tube decreases below a predetermined threshold

Question 13

What is the purpose of the control unit

Answer 13

The control unit identifies the normal and alarm conditions of the sensor with a measurement of the input resistance

Question 14

What is the local fire warning

Answer 14

When an alarm condition from the sensor is detected, the fire warning of the specific system is triggered, illuminating a red fire warning light on the overhead panel

Question 15

How long does a local warning stay on in the cockpit

Answer 15

As long as the fire detection loop detects a fire

Question 16

What type of systems are all essential fire warning systems

Answer 16

Dual loop

Question 17

How does a duel loop type of sensor work

Answer 17

A fire warning is only triggered if both sensors detect the fire at the same time. This AND logic prevents a false fire warning if one of the two sensors is set to the alarm condition due to a failure

Question 18

What type of detection system is not ideal for fire warning systems

Answer 18

The bi-metallic switch as it is easy to trigger and alarm

Question 19

What 3 main functions do all fire detection control units usually have

Answer 19

• They receive electrical signals from the sensors and identify the normal and alarm condition from this input signal. From the alarm condition the control unit activates the output signals which usually cause a fire warning
• The control unit in most systems can also identify fault conditions and activate the necessary functions
• It controls the test functions

Question 20

When would it be necessary to perform an operational test on the fire detection system to ensure it is working properly

Answer 20

Before each engine or APU start

Question 21

What does a fire detection operational test do

Answer 21

Simulates a fire or overheat condition for the control unit and ensures that the sensors are connected correctly

Question 22

How could you find a fault in a fire detection system

Answer 22

The central maintenance computer system can be used in modern aircraft

Question 23

What does each semiconductor loop consist of

Answer 23

A stainless steel tube filled with a semiconductor ceramic material with a wire in the centre

The ceramic material acts like an endless number of resistors. The resistors have an NTC characteristic, because of the semiconductor material

Question 24

How are all resistors connected in a semiconductor loop

Answer 24

In parallel on one side by the internal wire that is connected to the control unit. On the other side they are connected by the tube that is connected to the ground

Question 25

What manufacturer is the semiconductor loop type which contains 2 internal wires called

Answer 25

Kidde

Question 26

What manufacturers make the single internal wire loop type

Answer 26

Fenwal, Graviner or Edison

Question 27

What is the normal total resistance between all parallel resistors

Answer 27

Between 1mega ohms for long loop and 10mega ohms for short loops

Question 28

If there is a fire or overheat the resistance in the loop decreases below what resistance

Answer 28

500 ohms then the alarm is triggered

Question 29

If one loop detects a fault on a double loop system what would type of warning would a pilot receive in the cockpit

Answer 29

A loop fault message to identify a failure

Question 30

When installing new loops what maximum bend radius must not be exceeded

Answer 30

Not more than 3.2mm maximum, and no more than a minimum of 25.4mm must be obeyed

Question 31

What does a modern gas pressure loop consist of

Answer 31

Has two pressure switches and a resistor The first one is the monitor or integrity switch, it is normally closed due to the high gas pressure in the loop

Question 32

What is the amount of pressure found in a modern gas loop system

Answer 32

About two times higher than the ambient pressure at sea level

Question 33

What is the second switch in the pas pressure loop for

Answer 33

The alarm switch and closes at higher gas pressure, caused by overheat and fire

Question 34

What is the purpose of the resister inside the transponder on a gas pressure loop

Answer 34

It allows the control unit to identify which pressure switch is open or closed

Question 35

At what temperature does high gas pressure close the alarm switch for it to be triggered

Answer 35

When the complete loop is more than 200 Celsius or one small part is over 400 Celsius

Question 36

What type of indication would a pilot receive if a loop is damaged

Answer 36

The gas pressure decreases and the monitor switch opens This will trigger the fault warning

Question 37

What are the main components of a basic fire extinguishing system

Answer 37

- The extinguisher bottle - The discharge head with the cartridge - The piping with the spray nozzle The system also needs electrical circuits for system control and monitoring

Question 38

What are fire extinguisher bottles made from

Answer 38

It is a spherical stainless steel container

Question 39

What fire extinguishing agent do the fire extinguishing bottles contain

Answer 39

Halon 1301 in a liquid format

Question 40

How is the extinguishing agent pressurised in the bottles

Answer 40

It is pressurised by nitrogen at around 600psi at 20 degrees Celsius This guarantees the complete discharge of the bottle when it is used

Question 41

What does the size and weight of a fire bottle depend on

Answer 41

The amount of halon that is necessary to extinguish a fire in a compartment

Question 42

Where are the largest fire bottles located

Answer 42

Cargo compartments - weight around 20KG Engine bottles - Weight around 10KG APU - Weight around 5KG

Question 43

When would the weight of a fire bottle be checked

Answer 43

During a C-check

Question 44

What is the purpose of weighing the extinguisher bottle

Answer 44

The measured bottle gross weight must be the same as marked on the bottle. The bottle is measured with out the discharge head. A correct result would indicate there has been no leakage

Question 45

How is the halon discharged from the bottle

Answer 45

Through the discharge head and an electrically controlled cartridge that is installed in the bottom of the discharge head

Question 46

Is it possible for a bottle to have more than one discharge head

Answer 46

Usually only one discharge head is found however ones with two and three do exist. The amount of discharge heads represent how many individual cylinders the bottle has. The heads will be identical

Question 47

How much explosive powder does the discharge cartridge in the centre of the discharge head contain

Answer 47

Around 400 milligrams of explosive powder

Question 48

How does the powder in the discharge cartridge explode

Answer 48

When an electric current heats up a wire inside the cartridge. The wire is named the squib. The explosion of the cartridge is normally controlled by the electrical firing circuit

Question 49

Who is permitted to handle the discharge cartridge

Answer 49

A person licensed to work with class C explosives

Question 50

When removing the discharge cartridge what must be placed on it to prevent from exploding due to static electricity

Answer 50

An approved electrostatic protective cap is always installed to prevent any explosion due to static electricity

Question 51

What is the maximum service life of a discharge cartridge

Answer 51

6 years

Question 52

What is the purpose of the pressure switch on fire bottles

Answer 52

It controls a light on the fire panel in the cockpit when the bottle pressure decreases below 50% of the normal pressure

Question 53

Some bottles have a pressure gauge for maintenance checks. When reading the gauge what must an engineer be mindful of

Answer 53

The bottle pressure changes with temperature

Question 54

In the case of an emergency the frangible disk on fire bottles has a pressure relief function. At what temperature will the disk brake

Answer 54

At around 1700psi

Question 55

The fire extinguisher bottle has an extra overpressure relief valve when the bottle and the spray nozzle are in different compartments. How does this work and where would you find it

Answer 55

On the APU. The relief valve is a thermal fuse which melts when the temperature exceeds a safe value

Question 56

What is the purpose of the yellow disk

Answer 56

It is on the fuselage near the red disc The yellow disc is pushed out by a small piston if the bottle discharges via the spray nozzles

Question 57

Systems must be isolated when there is a fire, which is done automatically and which is done manually

Answer 57

The APU is done automatically and the engines must be done manually via the fire handle, this cuts off fuel and hydraulic supply to the engines

Question 58

To make the firing circuit as safe as possible what is done to make sure there is always power supplying the circuit

Answer 58

It is connected to the hot battery bus which is always connected by the batteries

Question 59

How could you ensure the squib is still serviceable

Answer 59

A squib test can be carried out in the cockpit either on the squib panel or the fire panel. If the squib light comes on the system is ok and if there is no light there is a brake in the system

Question 60

Why must you be careful when replacing the squib bulb in the cockpit

Answer 60

If a bulb which requires a higher current is used the current could be enough to fire the squib

Question 61

For engine fire systems what do regulations state with regards to fire bottles

Answer 61

They require a 'two shot' system. This means that the content of two fire extinguisher bottles can be discharged in to one engine

Question 62

Before discharging the extinguishing agent in an engine what must be done first

Answer 62

Engine shut down is required and isolate it from all of its supplies

Question 63

When the fire button is pressed what functions happen

Answer 63

- The engine driven generator Is switched off because the generator control relay and the generator power relay open - The bleed air valve closes - The low pressure fuel shut off valve closes - The hydraulic valve closes - The central warning system gets a signal and updates the ECAM displays - The fire bottles become armed

Question 64

What is different about each bottle on a 4 engines aircraft

Answer 64

They have 2 heads as they supply the engines in pairs

Question 65

Where is the APU fire bottle located

Answer 65

In the stabiliser in front of the APU firewall Only a 1 shot system is required for the APU

Question 66

Where is the APU fire test done

Answer 66

On the CMC to ensure the bottle doesn't fire