11.8 Fire Protection Flashcards
What does a complete fire detection system include?
Fire detection system and extinguishing.
What are the designated fire zones on an aircraft?
Engines and APU
Baggage and cargo
Lavatories
Avio bay
Wheel wells
Bleed air ducts
What is a fire warning system?
To alert the flight crew of a fire or of an overheat condition that could lead to a fire
What are the most common detectors?
Thermal switches
Thermocouples
Continuous loop sensing
How does a thermocouple work?
Depends on the rate of temperature change and does not give a warning when an engine slowly overheats or a short circuit develops.
What does a thermocouple system contain?
Relay box, warning lights and thermocouples.
What can the wiring system of a thermocouple system be divided into?
Detector
Alarm
Test
What does a relay box contain?
Two relays, sensitive relay, slave relay and thermal test unit.
What size current causes the relay to close?
4 milliamperes
What are the two widely used continuous loop systems?
Thermistor- Kiddle and Fenwal
Pneumatic pressure detectors- Systron-Donner
How is the fenwal system constructed?
Uses an inconel tube which contains a thermally sensitive eutectic salt and a nickel wire centre conductor.
How does the fenwal system work?
When heated the resistance of the eutectic salt drops and allows current flow.
What two packings can be found in fenwal wires?
Ceramic beads with eutectic salts.
Aluminium oxide suspended in fibre glass
How is the Kidde system constructed?
Two wires which are embedded in an Inconel tube filled with a thermistor core material. Two electrical conductors go through the length of the core.
How does the kidde system work?
One conductor has a ground connection to the tube, and the other conductor connects to the fire detection control unit. As the temperature of the core increases, electrical resistance to the ground decreases.
In the kidde system how is it identified if its a electrical short or fire?
The time taken for the change in resistance reset after initial warning.
What is a dual loop system?
Two complete basic fire detection systems with their output signals connected so that both must signal to result in a fire warning.
What logic does a dual loop system use?
AND
What is the benefit of AND logic in dual loop systems?
Greater increased reliability against false fire warnings.
Can a dual loop system be ran on one loop?
Yes the MEL permits it for dispatch.
How does a pneumatic continuous loop system work?
Contained gas expanding due to the heat.
When is the average temp sensor in a pneumatic system triggered?
In the range of 93 °C to 371 °C.
How does discrete temp sensing work?
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 for 5 seconds.
Are averaging and discrete temp sensing reversible?
Yes
What systems use a stainless steel tube filled with helium gas and a length of titanium wire?
Linberg, systron-donner and meggitt.
What causes an intermittent alarm in the fire detection system?
Intermittent short
What are the two types of detector used in a smoke detector system?
Photoelectric (Comparison and refraction types)
Ionisation
How do refraction smoke detector units work?
A photoelectric cell is placed at 90 degrees to a light beam, if smoke passes through it refracts the light onto the photodiode.
How does an Ionisation smoke detector work?
An electrode with a very small amount of radioactive material on one side of the detection chamber.
What aircraft are required to have smoke detectors in the lavatories?
Aircraft that can carry 20 or more passengers.
What is HRD?
High Rate Discharge
What is the most common extinguishing agent used today?
Halon 1301.
What makes up the discharge valve?
Squib and diaphragm
What are the two types of cartridge disk release?
Standard release type
High temp/hermetically sealed
What are the two types of discharge indicator?
Red- Thermal discharge
Yellow- Discharge
What is the regulation for engine fire extinguishing?
They must be two shot.
What does the check valve do on the bottle?
Prevents the second bottle filling the first empty one when discharged.
What 4 things cause an APU to auto-shutdown?
Fire
Oil overpressure
Overspeed
Overheat
What is the discharge cartridges service life?
5 to 10 years.
In the cargo extinguishing system what is the dump and metered systems?
Dump is the first bottle
Metered, slow and controlled.
At what tempo is cargo extinguishing system discharged?
76 degrees c
What happens if a fire test is carried out on the ground with only batteries in use?
Squib and discharge light come on with no ECAM warning
Red APU FIRE PBA light partially light comes on
Do lav fire extinguishers have the facility to be tested?
No, once they have low pressure they must be changed.
How many fire extinguishers be found on aircraft with 201-300 pax?
4
How many fire extinguishers be found on aircraft with 601+ pax?
8
What type of halon is used in hand held extinguishers?
1211
What class fires can be controlled with halons?
A,B or C
What are Co2 extinguishers used for?
On the ramp for external fires.
What is the only all purpose A/B/C dry powder extinguisher?
Mono-ammonium
What are class A fires best dealt with?
Water
What is a Class A cargo compartment?
Visual smoke detection, accessible in flight.
What is a Class B cargo compartment?
Each compartment to have its own detection and hand held extinguisher.
What is a Class C cargo compartment?
Cargo compartments found in wide bodied aircraft.
What is a Class D cargo compartment?
No longer used, became C or E
What is a Class E cargo compartment?
Cargo compartment covering whole main deck.
