particular airplane. For the purposes of this handbook, in- flight fires are classified as in-flight engine fires, electrical  fires, and cabin fires. However, consideration must be given to the possibility that  a wing could be seriously impaired and lead to structural  failure. Even a brief but intense fire could cause dangerous  structural damage. In some cases, the fire could continue to  burn under the wing (or engine cowling in the case of a single- engine airplane) out of view of the pilot. Engine compartment  fires that appear to have been extinguished have been known  to rekindle with changes in airflow pattern and airspeed. An in-flight engine compartment fire is usually caused by a  failure that allows a flammable substance, such as fuel, oil,  or hydraulic fluid, to come in contact with a hot surface. This  may be caused by a mechanical failure of the engine itself,  an engine-driven accessory, a defective induction or exhaust  system, or a broken line. Engine compartment fires may also  result from maintenance errors, such as improperly installed/ fastened lines and/or fittings resulting in leaks. The pilot must be familiar with the airplane’s emergency  descent procedures. The pilot must bear in mind the following: Engine compartment fires can be indicated by smoke and/ or flames coming from the engine cowling area. They can  also be indicated by discoloration, bubbling, and/or melting  of the engine cowling skin in cases where flames and/or  smoke are not visible to the pilot. By the time a pilot becomes  aware of an in-flight engine compartment fire, it usually is  well developed. Unless the airplane manufacturer directs  otherwise in the AFM/POH, the first step on discovering a  fire should be to shut off the fuel supply to the engine by  placing the mixture control in the idle cut off position and the  fuel selector shutoff valve to the OFF position. The ignition  switch should be left ON in order to use up the fuel that  remains in the fuel lines and components between the fuel  selector/shutoff valve and the engine. This procedure may  starve the engine compartment of fuel and cause the fire to  die naturally. If the flames are snuffed out, no attempt should  be made to restart the engine. The initial indication of an electrical fire is usually the distinct  odor of burning insulation. Once an electrical fire is detected,  the pilot should attempt to identify the faulty circuit by  checking circuit breakers, instruments, avionics, and lights.  If the faulty circuit cannot be readily detected and isolated,  and flight conditions permit, the battery master switch and  alternator/generator switches should be turned off to remove  the possible source of the fire. However, any materials that  have been ignited may continue to burn. If the engine compartment fire is oil-fed, as evidenced by  thick black smoke, as opposed to a fuel-fed fire, which  produces bright orange flames, the pilot should consider  stopping the propeller rotation by feathering or other means,  such as (with constant-speed propellers) placing the pitch  control lever to the minimum rpm position and raising the  nose to reduce airspeed until the propeller stops rotating. This  procedure stops an engine-driven oil (or hydraulic) pump from  continuing to pump the flammable fluid that is feeding the fire. If electrical power is absolutely essential for the flight,  an attempt may be made to identify and isolate the faulty  circuit by: Some light airplane emergency checklists direct the pilot  to shut off the electrical master switch. However, the pilot  should consider that unless the fire is electrical in nature, or a  crash landing is imminent, deactivating the electrical system  prevents the use of panel radios for transmitting distress  messages and also causes air traffic control (ATC) to lose  transponder returns. Pilots of powerless single-engine airplanes are left with no  choice but to make a forced landing. Pilots of twin-engine  airplanes may elect to continue the flight to the nearest airport.  Cabin fires generally result from one of three sources: (1)  careless smoking on the part of the pilot and/or passengers;  (2) electrical system malfunctions; (3) heating system  malfunctions. A fire in the cabin presents the pilot with  This procedure, however, has the effect of recreating the  original problem. The most prudent course of action is to  land as soon as possible. Engine Fire Electrical Fires Cabin Fire 17-8 • The airplane may be severely structurally damaged to  the point that its ability to remain under control could  be lost at any moment. • The airplane may still be on fire and susceptible to  explosion. • The airplane is expendable and the only thing that  matters is the safety of those on board. 1.  Turning the electrical master switch OFF. 2.  Turning all individual electrical switches OFF. 3.  Turning the master switch back ON. 4.  Selecting electrical switches that were ON before the  fire indication one at a time, permitting a short time  lapse after each switch is turned on to check for signs  of odor, smoke, or sparks.