11.8 Fire And Smoke Detection

Question 1

What are three things needed for a fire to occur?

Answer 1

Fuel, heat and oxygen

Question 2

What are the designated zones on aircraft that have fixed fire detection and/or fire extinguishers?

Answer 2

Engines and APUs, baggage and cargo compartments, lavatories, electrical/electronic equipment compartment, wheel wells, bleed air ducts

Question 3

What are the possible fire detection systems on reciprocating engines or small turboprop aircraft?

Answer 3

Overheat detectors, rate if temperature rise detectors, flame detectors, observation by crew members

Question 4

What are the fire protection systems used on large engine aircraft?

Answer 4

Rate of temperature rise detectors, radiation sensing detectors, carbon monoxide detectors, combustible mixture detectors, optical detectors, observation by flight/cabin crew or passengers

Question 5

How does the pilot know if there is overheating?

Answer 5

It comes up on the flight deck controls

Question 6

What are the three most common detectors or sensing devices?

Answer 6

Thermal switches, thermocouples, continuous loop sensing elements

Question 7

How do thermal switch systems work?

Answer 7

They are heat sensitive units that compete electrical circuits at a certain temperature

Question 8

How does a thermocouple system work?

Answer 8

Constructed of two dissimilar metals, such as chromel and constantan. The point at which these metals are joined and exposed to the heat of a fire is called a hot junction

Question 9

What can the wiring system on a thermocouple be divided into?

Answer 9

Detector circuit, alarm circuit, test circuit

Question 10

Where do large aircraft use continuous loop systems?

Answer 10

Power plants, pneumatic manifolds and wheel well protection

Question 11

What is the difference between Fenwall and Kidde sensing element?

Answer 11

Fenwall only has one inner inconel tube where kidde has two

Question 12

What are the two tubes in the kidde sensing element?

Answer 12

Conductor, earth wire soldered to tube

Question 13

How do you earth the Fenwall tube?

Answer 13

With the inconel tube

Question 14

Why are dual loop systems important

Answer 14

Because if one is found inoperative then the other can pick it up, it also prevents false warning to be generated

Question 15

How does a pneumatic continuous loop system work?

Answer 15

Contained gas expanding due to the application of heat

Question 16

Pneumatic detector has two sensing functions what are they?

Answer 16

Overall average temperature threshold, localised discrete temperature increase that was caused by a flame or hot gases

Question 17

What principle does a pneumatic continuous-loop system work on?

Answer 17

Contained gas expanding due to heat

Question 18

How does a pneumatic continuous loop system prevent false readings with the damage?

Answer 18

Any severe damage to the unit will provide a no test indication not a false alarm

Question 19

What are the two sensing functions on a pneumatic continuous loop system?

Answer 19

An overall average temperature threshold and a localised discrete temperature increase that was caused by a flame or hot gas

Question 20

How does the average temperature sensing work on a continuous loop system?

Answer 20

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

Question 21

How does discrete temperature sensing work?

Answer 21

Discrete sensing is accomplished using a hydrogen-filled core material in the sensor tube. Hydrogen gas is released from the detector core whenever a small section of the tube is heated to a pre-set discrete temperature within the range of 1100 °C (2000 °F) for 5 seconds

Question 22

Where are fire detector systems tend to be found?

Answer 22

High activity areas

Question 23

Where can you find smoke detectors on aircraft?

Answer 23

Cargo and baggage, equipment bays and lavatories

Question 24

What are the two basic types of smoke detectors?

Answer 24

Photoelectric (comparison and refraction types) and ionisation type

Question 25

How does a refraction photoelectric system work?

Answer 25

Air is sampled through a chamber, a light is going into the light trap, if the smoke cuts off the light then the alarm will go off

Question 26

How does an ionisation type smoke detector work?

Answer 26

Has an electrode with a very small amount of radioactive material on the inside and an electrode opposite it. When smoke enters there is less of a reaction meaning if it falls below a set value it goes off

Question 27

How does a cargo smoke detector work?

Answer 27

It detector utilises an optical smoke detector which consists of source Light Emitting Diodes (LEDs), intensity monitor photodiodes, and scatter detector photodiodes

Question 28

Where are the cargo smoke detectors located?

Answer 28

Each compartment

Question 29

What aircraft require smoke detectors in the toilets?

Answer 29

Ones that can carry 20 or more people

Question 30

How can the flight crew detect a fire in the toilet?

Answer 30

Either a sound or light to the flight deck or the flight attendant station

Question 31

What is the lavatory smoke detector powered by?

Answer 31

28vdc (Volts, Direct, Current)