11.8 Fire And Smoke Detection Flashcards
What are three things needed for a fire to occur?
Fuel, heat and oxygen
What are the designated zones on aircraft that have fixed fire detection and/or fire extinguishers?
Engines and APUs, baggage and cargo compartments, lavatories, electrical/electronic equipment compartment, wheel wells, bleed air ducts
What are the possible fire detection systems on reciprocating engines or small turboprop aircraft?
Overheat detectors, rate if temperature rise detectors, flame detectors, observation by crew members
What are the fire protection systems used on large engine aircraft?
Rate of temperature rise detectors, radiation sensing detectors, carbon monoxide detectors, combustible mixture detectors, optical detectors, observation by flight/cabin crew or passengers
How does the pilot know if there is overheating?
It comes up on the flight deck controls
What are the three most common detectors or sensing devices?
Thermal switches, thermocouples, continuous loop sensing elements
How do thermal switch systems work?
They are heat sensitive units that compete electrical circuits at a certain temperature
How does a thermocouple system work?
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
What can the wiring system on a thermocouple be divided into?
Detector circuit, alarm circuit, test circuit
Where do large aircraft use continuous loop systems?
Power plants, pneumatic manifolds and wheel well protection
What is the difference between Fenwall and Kidde sensing element?
Fenwall only has one inner inconel tube where kidde has two
What are the two tubes in the kidde sensing element?
Conductor, earth wire soldered to tube
How do you earth the Fenwall tube?
With the inconel tube
Why are dual loop systems important
Because if one is found inoperative then the other can pick it up, it also prevents false warning to be generated
How does a pneumatic continuous loop system work?
Contained gas expanding due to the application of heat
Pneumatic detector has two sensing functions what are they?
Overall average temperature threshold, localised discrete temperature increase that was caused by a flame or hot gases
What principle does a pneumatic continuous-loop system work on?
Contained gas expanding due to heat
How does a pneumatic continuous loop system prevent false readings with the damage?
Any severe damage to the unit will provide a no test indication not a false alarm
What are the two sensing functions on a pneumatic continuous loop system?
An overall average temperature threshold and a localised discrete temperature increase that was caused by a flame or hot gas
How does the average temperature sensing work on a continuous loop system?
It is activated by the expansion of a fixed volume of helium gas inside the detector
How does discrete temperature sensing work?
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
Where are fire detector systems tend to be found?
High activity areas
Where can you find smoke detectors on aircraft?
Cargo and baggage, equipment bays and lavatories
What are the two basic types of smoke detectors?
Photoelectric (comparison and refraction types) and ionisation type
How does a refraction photoelectric system work?
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
How does an ionisation type smoke detector work?
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
How does a cargo smoke detector work?
It detector utilises an optical smoke detector which consists of source Light Emitting Diodes (LEDs), intensity monitor photodiodes, and scatter detector photodiodes
Where are the cargo smoke detectors located?
Each compartment
What aircraft require smoke detectors in the toilets?
Ones that can carry 20 or more people
How can the flight crew detect a fire in the toilet?
Either a sound or light to the flight deck or the flight attendant station
What is the lavatory smoke detector powered by?
28vdc (Volts, Direct, Current)
