15.20 fire protection systems

Question 1

what is a fire zone?

Answer 1

designated by the manufacturer to require fire detection and/ or fire extinguishing systems as well as a high degree of fire resistance

Question 2

what is thermodynamic turbine failure?

Answer 2

an upset to the quantity of of air used to cool down combustion temperatures, turbines can melt causing a sudden loss in thrust

Question 3

what can cause thermodynamic turbine failure?

Answer 3

Ice, excess bleed air etc

Question 4

what is mechanical turbine failure?

Answer 4

fractured or thrown blades

Question 5

what can occur as a result of mechanical turbine failure?

Answer 5

damage to the turbine housing

Question 6

what is contained in a complete fire detection system?

Answer 6

fire detection and extinguishing

Question 7

what are the common detectors used?

Answer 7

overheat
rate of temp rise
flame detectors

Question 8

what are the two most common types of fire detection systems?

Answer 8

spot and continuous loop

Question 9

how does a spot detector function?

Answer 9

individual sensors to monitor a fire zone

Question 10

which aircraft use a thermal switch or thermocouple design?

Answer 10

older

Question 11

what is the structure of a thermal switch design?

Answer 11

A thermal switch system comprises one or more lights energised by the aircraft’s power system and thermal switches that control the operation of the light(s). These thermal switches are heat-sensitive units that complete electrical circuits at a set temperature

Question 12

how are thermoswitches connected?

Answer 12

They are connected in parallel with each other, but in series with the indicator lights

Question 13

what is the disadvantage of the thermocouple?

Answer 13

A thermocouple depends on the rate of temperature rise and does not give a warning when an engine slowly overheats, or a short circuit develops.

Question 14

how is the wiring system divided for a thermocouple?

Answer 14

Detector circuit
Alarm circuit
Test circuit

Question 15

what principle do optical fire detectors function on?

Answer 15

they alarm when they detect the presence of specific radiation emissions from hydrocarbon flames

Question 16

what are the two types of optical fire detectors?

Answer 16

Infrared (IR) and ultraviolet,

Question 17

how does a pneumatic fiure detector function?

Answer 17

The sensing element consists of a closed helium-filled tube connected at one end to a responder assembly

gas pressure inside the tube increases until the alarm threshold is reached. At this point, an internal switch closes

Question 18

how does an average sensing function work?

Answer 18

it is activated by the expansion of a fixed volume of helium gas inside the detector

Question 19

how does discrete temp sensing function on pneumatic fire detectors

Answer 19

Discrete sensing is accomplished using a hydrogen-filled core material in the sensor tube.
Hydrogen is released from the detector core if a small section of the tube is heated to a discrete temperature
This outgassing in the core will increase the pressure and activate the alarm

Question 20

are the discrete and average temp sensing in the pneumatic fire detector reversible?

Answer 20

yes

Question 21

what are the two widely used types of continuous loop detectors?

Answer 21

fenwal
kidde

Question 22

what is the fenwal systems structure?

Answer 22

The Fenwal system uses a slender Inconel tube packed with thermally sensitive eutectic salt and a nickel wire centre conductor. Lengths of these sensing elements are connected in series to a control unit

Question 23

how does the fenwel system function?

Answer 23

When an overheat condition occurs at any point along the element length, the resistance of the eutectic salt within the sensing element drops sharply, causing current to flow between the outer sheath and the centre conductor

Question 24

how does kidde differ from fenwel?

Answer 24

it has two embedded wires

Question 25

what do the two wires in the kidde system connect to?

Answer 25

one to the tube
one to the fire detection control unit

Question 26

how is a detection system tested?

Answer 26

through a switch in the cockpit

Question 27

what is the benefit of a dual loop system?

Answer 27

both must sense the alarm condition to know there is a fire limiting false alarms

Question 28

what must all engines have in terms of extinguishers?

Answer 28

a two shot system

Question 29

how does a fixed fire extinguisher function?

Answer 29

it gives of an inert gas to not support combustion

Question 30

why do we use halon 1301?

Answer 30

it is not corrosive, toxic etc

Question 31

when can cylindrical fire bottles be used?

Answer 31

when space is a concern

Question 32

what is the typical fire bottle shape?

Answer 32

cylindrical

Question 33

what is installed in a discharge valve of a fire bottle?

Answer 33

a cartridge (squib)
tangible disc type valve

Question 34

what are the other types of available discharge valves on fire bottles?

Answer 34

solenoid-operated or manually operated seat-type valves. Two types of cartridge disk release techniques are used. The standard release type uses a slug driven by explosive energy to rupture a segmented closure disc

Question 35

how can you know the pressure of a fire extinguisher charge?

Answer 35

A simple visually indicated gauge is available, typically a vibration-resistant helical Bourdon-type indicator

Question 36

when is a two way check valve used on fire bottles?

Answer 36

when a two shot system is in place

Question 37

what occurs when a fire switch is activated?

Answer 37

the engine stops
the extinguishing system is armed