I once had a ground instructor at TWA who used to tell his students, with tongue in cheek, that there was little to fear from a jet engine fire. "After all," he would say, "these engines are always on fire."
In one respect, he was right. The modern turbine engine rarely catches fire. When a fire bell does sound, the emergency most often is resolved by moving the thrust lever to the idle position, because such a warning typically is caused by a leaking hot-air duct. If the fire is for real, it then becomes a relatively simple matter of shutting down the engine; pulling a single handle to shut off that engine's fuel, oil, and hydraulic fluid supply; and possibly discharging one or more fire bottles. It is an extremely rare event for an engine fire to survive these procedures. The problem is a bit more serious, of course, in a turbine single.
I don't mean to imply that an engine fire in a turbine airplane is not serious, but it typically is not nearly as much of a concern as an engine fire in a piston-powered airplane, single or twin.
General aviation accidents caused by engine fires are thankfully rare, occurring about 18 times per year. But for that handful, few events can occur in an airplane that are likely to generate as much fear. Consider this advice offered by Britain's Royal Air Force to its piston pilots: "Landing with an engine on fire is seldom justified. There is little chance of saving the aircraft after landing, and there is great risk that the fire may increase and cause structural failure at an altitude where it is unsafe to abandon the aircraft." (This option is not available to civilian pilots.)
Engine fires are most often caused by mechanical failure of the engine or an engine-driven accessory; defects in the induction or exhaust system; a flooded carburetor (caused by a sticking float valve); or a leak in the fuel, oil, or hydraulic system. (Leaks detected during a preflight inspection are a compelling reason to postpone a flight.)
Although the sight of flames or smoke is convincing evidence of a fire, these are not always the first indications. Several survivors of engine fires have reported that they were alerted by heat near the rudder pedals. Others were warned by the smell of smoke. One pilot said that he first noticed reduced fuel pressure and thought that the fuel pump was failing. The flames that developed shortly thereafter made him realize that the pressure loss was instead caused by a serious leak.
In theory, the firewall separating the engine from the cabin is supposed to keep a fire at bay, but it doesn't usually work that way. Firewalls are fire-resistant, not fireproof. Only the variables of airspeed, flame intensity, and time of exposure will determine how long the firewall can maintain its integrity.
The danger of allowing an engine fire to continue in a twin is equally dangerous. Once a firewall begins to fail, the very structure of the wing is in jeopardy. And should the flames lick at a nearby fuel tank, the results can be explosive.
Once an engine fire begins, no time can be spent hunting for a checklist. Step one should have been committed to memory and requires the immediate shutdown of the engine, irrespective of the type of terrain below. A controlled crash landing is preferable to airborne cremation.
Shutting down—closing the throttle, pulling the mixture control to idle cutoff, and turning off both the fuel selector and electric fuel pump—deprives the fire of combustible fluids and, with luck, may allow the fire to die of natural causes. But even if the flames and smoke seem to disappear, a pilot must not assume that the problem has been resolved. The fire might only have diminished temporarily, or the flames might be coming out the bottom of the cowling. Under no circumstances should a restart be considered. The fire might start anew with even greater enthusiasm.
If the fire cannot be extinguished in short order, a pilot might be faced with the possibility of asphyxiation. To prevent smoke from entering the cockpit, close all fresh-air vents located in the firewall and near the sides of the fuselage. Vents located free of streaming smoke should be opened to increase the flow of fresh air through the cabin. If the cabin does fill with smoke, opening a door or a window on the right side of the airplane may clear the cockpit of contaminated air. Venting the left side of the cockpit can worsen the problem by forcing smoke to pass in front of the pilot's face. (On many jetliners, smoke removal procedures involve opening the copilot's sliding-glass window, a procedure that has the unanimous approval of captains.)
Is it possible to blow out an engine fire by diving at high speed? Perhaps, but increasing airflow across the engine could cause fire intensity to increase, depending on the combustible mixture. Increasing airspeed encourages the burning of a rich mixture but may extinguish a lean mixture. Trouble is, a pilot cannot afford the time needed to make this determination.
Step two in coping with an engine fire is making a rapid descent and landing as soon as possible. But many pilots do not know the most expeditious way to get down, a procedure for which there can be other incentives. We'll discuss this next month.
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