Chapter 6 - Aircraft Fire Protection System Flashcards
What are the most common causes of fire onboard an aircraft?
Fuel leaks in the vicinity of hot equipment
Hot gas leaks, from engines or ducting, impinging on inflammable materials
Electrical or mechanical malfunctions in equipment
Fire and overheat detectors sense the presence of fire or excessive heat. What are the types of detector used?
Area detectors - Deployed in large fire zones
Spot detectors - Used for individual pieces of equipment
Name two types of fire detector found on aircraft.
Thermal switch
Continuous element (firewire)
How does a thermal switch work?
Two contacts in a bowed shape within a cylinder, pressure from the cylinder walls keeps them bowed and apart. At normal operating temperatures they do not touch.
As temperature rises, the cylinder expands and the contacts come together. Sends a warning to the cockpit and fire detection system of an overheat/fire.
As tube cools the contacts come apart again and the warning stops.
How does a continuous element (firewire) fire/overheat detector work?
A stainless steel tube contains filling material with a central electrode running through the centre.
An electrical pulse can only pass through the central electrode as the filling acts as an insulator. When extreme heat is applied to the continuous ‘wire’, the filling material warms and its resistance begins to decrease, making it a less effective insulator.
Eventually, current from the central electrode is able to reach the exterior casing, thereby completing a circuit which alerts the crew.
Heat source removed = Insulator/filling cools, resistance increases again, circuit broken and warning removed.
What are the functions of a fire detection system?
Monitor designated areas or equipment for a rise in temperature
Provide a warning to the crew
Complete electrical safety circuits within the fire extinguisher systems, to permit necessary operation by the crew
What must the pilot do first before discharging an engine fire extinguisher/fire bottle system?
Stop the fuel supply to the engine and shut it down
What is a two shot fire extinguisher system?
The pilot has two attempts to extinguish the fire, the first with the respective engines Fire Bottle and the second with the Fire Bottle for the other engine.
What extra fire protection is provided to protect the aircraft from the heat?
Fire walls between the engines and the rest of the aircraft, usually made of Titanium.
What is the fire tetrahedron?
Need - Fuel, Oxygen and an Ignition Source to start and maintain a fire.
Combustion is on the bottom of the fire tetrahedron.
How does a Halon fire extinguisher work?
Breaks the chain reaction, stopping the fuel, ignition and oxygen (3 elements of the fire triangle) by CHEMICALLY DISRUPTING COMBUSTION (4th element for the fire tetrahedron).
What inert gases make up Halon?
Bromine, Chlorine, Fluorine and Methane
What are the possible side effects and risks associated with Halon fire extinguishers?
Chilled skin and Frostbite
Damage to eyes and skin, even without direct contact
Inhalation of large amounts of Halon gas can cause dizziness, a tingling sensation in the extremities, and in some cases unconsciousness
Suffocation - High concentrations of Halon can create an oxygen deficient environment, causing people to suffocate
Are thermal switches used as spot or area detectors?
Spot detectors
Are continuous element (firewire) detectors used as spot or area detectors?
Area detectors
