Aircraft Fires


You can help prevent a fire by thoroughly inspecting your aircraft before flight, and you can be prepared by having a fire extinguisher always at hand.

Prevention strategies and what to do if it happens to you

By Robert N. Rossier

Fire is a mixed blessing.

On the ground, knowing how to start a fire can save your life in a survival situation. In an airplane, fire is a four-letter word. If you aren't prepared to extinguish it, your chances of survival are slim at best.

Among the most common emergency procedures that pilots practice are engine failures, instrument failures (particularly for instrument-rated pilots), and various system failures such as flaps, propellers, alternators, and brakes. But when was the last time you practiced the emergency procedures for a fire, either on the ground or in the air?

The chances of having a fire are slim, but reacting quickly and correctly is essential to effectively dealing with the emergency. When a fire erupts, you may have little time to consult the emergency checklist, and if you're confused or uncertain about the procedures, your reactions may be slow and inappropriate.

Fire basics

A fire needs only three ingredients — fuel, air, and an ignition source (heat). Put these three ingredients in the proper juxtaposition, and voila — fire. Unfortunately, a running aircraft has plenty of hot things that can quickly ignite a fire. Most of them are under the cowling, where a fire rages inside the engine. The cylinders contain the fire, but they also absorb the heat and can warm to a few hundred degrees — hot enough to ignite many combustibles.

But a fire is more likely to occur under the cowl when a component fails because of age, fatigue, or improper maintenance. A cherry-red turbocharger or a crack in the exhaust system or a cylinder can ignite the spray from a broken fuel or oil line to create an impromptu blast furnace.

Electrical power from alternators, generators, and batteries constitutes another potential heat source. With power routed to virtually every part of the aircraft for lighting, deicing, radios, landing gear and flap motors, and fuel pumps, the electrical system is another prime candidate for starting fires. Insulation, adhesives, and fabrics make great fuel for fire, as does the insulation on the wiring itself. Leaking avgas from a primer or fuel-flow gauge, or dripping fluid from a brake cylinder are also excellent fuels that an errant electrical spark can ignite.

Although the engine and electrical system constitute the primary ignition sources, they aren't the only causes of fires. Witness ValuJet flight 592, where oxygen canisters ignited and caused a fatal crash. Butane lighters have also been known to explode at altitude, and although smoking is not allowed on commercial flights, it's an obvious fire hazard on any aircraft.

In one incident, an Aerospatiale Tobago (TB10) was being taxied to check an instrument repair. When the pilot depressed the left brake pedal, it went to the floor, and the brake failed. Using rudder and the right brake, the pilot was able to taxi back to the ramp. A bystander was the first to notice that the left main wheel was on fire. What happened? The compression fitting that attached the brake line to the brake failed, and when the pilot stepped on the brake pedal, it squirted brake fluid onto the hot brake disk. It took seven 20-pound fire extinguishers to put out the fire. The pilot evacuated the aircraft quickly and wasn't injured.

If starting a fire is a matter of combining fuel, air, and an ignition source, it stands to reason that removing one of these ingredients will extinguish a fire. That's the premise of most emergency checklists for fire, but the checklist is also designed to help minimize damage, deal with the smoke, and get the aircraft on the ground quickly and safely.

Pilots can face four types of aircraft fires — fires during engine start, electrical fires, in-flight engine fires, and post-crash fires. It's important that you understand the proper checklist procedures for each type and the reasons behind the checklist items.

Engine start

Perhaps the most common type of aircraft fire is one that erupts during engine start. A cold weather start is a perfect scenario for an engine fire, particularly if we get carried away with the primer. Excess fuel makes its way into the carburetor intake, then the engine backfires through the carburetor, igniting the fuel along with the dirty air filter.

The book says to keep cranking the engine if this happens. This should suck the flames back through the carburetor and extinguish the blaze, and if the engine starts, let it run for a minute or so, then shut it down and inspect the damage. If the engine doesn't start after cranking it for the time recommended by the checklist, shut down, evacuate the aircraft, and, if it's not already extinguished, use the extinguisher to put out the fire.

Detecting a fire on the ground isn't always easy. Sometimes the carburetor contains the blaze. Or the fire partially burns the inlet air filter — then the engine starts and snuffs it out. If you hear a backfire during the start, let the engine run a minute or two at higher than normal rpm, then shut down and inspect for damage.

Electrical Fires

By definition, electrical fires originate from electrical components. Often, we can detect an electrical fire before it really gets going. The first clue might be an over-voltage warning light, a higher than normal electrical load, or a popped circuit breaker. The acrid smell of hot insulation or visible white smoke also are common indicators — but don't be fooled. In one incident, white smoke filled the cabin of a Piper Arrow, leading the pilot and instructor to think they had an electrical fire. In reality, they had a fuel fire in the engine compartment, which had begun to melt the ducts that supply heated air to the cabin.

Once ignited, electrical fires burn just like any fire. One difference is that the heat from the energized electrical wiring or component that caused the fire might sustain it. For this reason, your first step if you have an electrical fire is to cut the power by turning off the master switch. By isolating the battery and alternator/generator, we remove the ignition source, and the fire should extinguish.

If the fire is already burning hot, cutting the power won't be enough. You'll need to use an extinguisher to squelch the flames — a tricky proposition if the fire is behind the instrument panel. Once the fire is out, some checklists suggest that we try to restore power and isolate its cause.

We can shut off all our electrical components, turn the master switch back on, and start turning on essential components one at a time. With any luck, a non-critical item will be the culprit, and we can continue on to land at the nearest airport.

Because reenergizing the circuits might recreate the situation that caused the fire in the first place, finding its cause might not be the best option. Another school of thought says we should communicate before cutting the power — if we have time — then refrain from reenergizing the system and possibly restarting the fire. This might mean a no-flap landing or lowering the landing gear manually, but it sure beats incapacitation and an early grave. It's a difficult decision to make, especially if we're on a night flight or in instrument conditions. A good flashlight (or three or four), a handheld transceiver, and a handheld GPS navigation receiver can come in real handy if a fire puts the electrical system out of commission.

If we have time to communicate before powering down the electrical system, we have three options. Call ATC, broadcast in the blind on the emergency frequency of 121.5 MHz, or tune the 7700 emergency code into the transponder and IDENT. Taking a few seconds to do any of these things before we shut down the electrical system might alert someone to the problem and bring fire/rescue services to the scene as we head for an airport. Finally, if it has a manual switch, we can activate the emergency locator transmitter. The beauty of the ELT is that it has its own power supply and will bring help to the scene of a forced landing should that become necessary.

Managing the smoke is another important part of dealing with an electrical fire. Here, too, you'll find different schools of thought. To continue breathing and to see well enough to maintain control of the aircraft, we might have to open the vents or vent window. Opening the pilot's vent window could be a mistake because it might pull the smoke right in front of the pilot, obscuring his vision.

Opening another vent, if available, or cracking a door might be a better option. Venting the smoke may improve breathing and vision — but it can also fan the fire's flames with fresh air. If this happens we have no option but to close the vents.

Regardless of how we handle the electrical system following a fire, continuing the flight any longer than is necessary is out of the question. An in-flight fire is extremely dangerous, and you must land immediately — at the nearest airport, if possible — but possibly at an appropriate off-airport site.

Engine fire in flight

Detecting an in-flight engine fire may not be as easy as we might think, but sometimes we can detect the fire's cause if we're observant. A drop in fuel pressure or a fluctuating fuel pressure reading may suggest a broken fuel line — a common precursor to an engine fire. A rough-running engine might be caused by a cracked cylinder, which can leak oil or hot gas and ignite a blaze.

Black smoke usually signals an oil fire, and fuel usually burns bright orange. By the time you get the "hot-foot" symptom, the fire is already blazing on the other side of the firewall. In-flight engine fires are different from electrical fires, and we use different tactics to deal with them. The checklists for engine fires vary, but usually the first step is to shut off the fuel supply. If we're flying a single-engine airplane, we might be tempted to run the engine until it gets us to safety, but this strategy can backfire. Unless we extinguish the blaze, we run the risk of a structural failure or an in-flight barbecue.

The typical checklist procedure for an in-flight engine fire is to pull the mixture to idle-cutoff and shut off the fuel selector. Because cabin heat ducting passes through the firewall into the cabin and because we want to keep the blaze on the engine side of the firewall, most checklists say to shut off the cabin heat.

Again, an engine fire may mean smoke in the cockpit, and various manufacturers recommend different ways to deal with it. As with an electrical fire, it may be advisable to open a vent or window, or crack open a door to remove the smoke, but you may want to choose one that's away from the pilot. In some aircraft, even a minor change in flap setting can alter the flow of air around the aircraft, which may affect how well windows and vents can clear cockpit smoke.

Be sure to read the pilot's operating handbook for every aircraft you fly — and make sure you thoroughly understand the proper procedures for each.

If a fire burns long and hot enough before it's discovered, shutting down the engine may not extinguish the blaze, and we'd have to take the next step, which might be a rapid descent. Increasing airspeed may blow out the fire. If that doesn't work, it's important to get the aircraft onto the ground as quickly as possible, before the fire causes structural damage and airframe failure. It seems contrary to our instincts, but you must point the nose toward the ground and land at the closest survivable location.

The second emergency

An in-flight engine fire is usually a two-fold emergency. First there's the fire, and then comes the harrowing adventure of making an emergency descent and landing — probably not to a runway. Here we may need to choose between slipping the aircraft to improve forward visibility, or keeping the nose straight to help blow out the blaze and get on the ground more quickly. Unfortunately, this is a learn-as-you-go situation.

At some point, we have to transition between the high-speed descent and the landing. To bleed off the speed, you might need to lower the flaps and gear, even if you're above the speed limit for doing so. Chances are the aircraft is going to undergo structural damage anyway, and slowing for the landing is your top priority. You should fasten seat belts, remove sharp objects from pockets, and complete any before-landing emergency actions such as opening doors or windows. The name of the game then is to keep flying the aircraft until it comes to a complete stop.

The post-crash fire

Aircraft fires often occur following forced landings, and the result is often more dangerous than the forced landing itself. The sad truth is that most light aircraft fuel systems are not designed to withstand crash impacts, and they often fail during a forced landing. Spilled fuel and hot crash components often result in a fuel-fed inferno.

The thought of being consumed by flames is horrifying, but smoke is often the real killer. Carbon monoxide (CO) is a major byproduct of a fire, and it's toxic even in minute quantities. CO combines with the hemoglobin in red blood cells, bonding strongly to the chemical sites that normally carry oxygen to the tissues.

CO isn't the only problem. Burning fabrics such as wool release toxic cyanide gas, and smoldering plastic can generate hydrochloric acid, phosgene (a nerve poison), as well as blindingly thick black smoke. This can be even more dangerous if the aircraft interior has been reupholstered with non-FAA approved materials.

Our most immediate objective is to get out of the aircraft as quickly as possible. Discharging the contents of a Halon fire extinguisher in the cabin immediately after the aircraft comes to a stop may help prevent a cabin fire from erupting for a few critical moments. An extinguisher also makes a great battering ram to knock out windows and force stubborn exits to open.

Prevention is the best cure

The best insurance against an aircraft fire is professional maintenance and a thorough preflight inspection. Always look for evidence of fuel, oil, and hydraulic leaks, and use your nose as well as your eyes. Carefully check under the cowl for bird nests, windblown debris, and misplaced rags. Check the exhaust stacks for security and cracks, and look for loose or leaking fittings on the brakes.

Before takeoff, test all the electrical components that you might use during flight, and watch for any indications of impending failure. A pitot heat switch that fails and burns is much easier to cope with on the ground than while you enter the clouds at 1,000 feet.

Fortunately, aircraft fires are relatively rare, but considering the serious consequences, particularly in flight, it's important to know the procedures for dealing with a fire, and to practice them often. Get out that emergency checklist, and make sure you know exactly what to do when a fire heats up your flying.

The right tools for the job

Dealing with an in-flight fire is a difficult proposition, but without the right tools it can be virtually hopeless. Part of your preflight check should include the fire extinguisher. Don't just see that it's there, look at its gauge and make sure it's in the green. Commercial operators must service, inspect, and weigh aircraft fire extinguishers monthly, and Part 91 operators should adopt a similar routine. Several types of extinguishers are commonly used for fighting aircraft fires, and it's important to distinguish between them. They have different characteristics, and some are better suited to particular situations than others.

Most general aviation aircraft use dry chemical extinguishers. Inexpensive and versatile, they extinguish class A (combustible materials such as paper air filters, foam seat cushions, rags, and birds' nests), class B (liquid fuel such as oil, hydraulic fluid and avgas), and class C (electrical) fires. Because you need to apply the chemical directly to the flames, putting out an electrical fire behind the instrument panel can be difficult.

Dry chemical extinguishers aren't the best choice for engine fires. If the engine ingests the chemical, it can caramelize on the valves and result in engine damage or failure. If you must use a dry chemical extinguisher to extinguish an engine fire on the ground, shut the engine down first by pulling the mixture to idle-cutoff. This not only keeps the engine from eating any chemicals, it robs the fire of fuel.

Using a dry chemical extinguisher in the cockpit during flight can have serious side effects. Flying powder from a short burst can cloud the cockpit and your vision, making it difficult, if not impossible, to read the instruments or control the aircraft. Also, some dry chemical extinguishers pose potential toxicity concerns, but if you consider the alternative — a raging fire — the choice is clear.

Carbon dioxide — CO2 — fire extinguishers are used to combat class B and C fires. The CO2 exits the nozzle at about minus 100 degrees F, forming fine particles of dry ice that condense moisture from the air, then quickly melt in the presence of a fire. These extinguishers extinguish a fire by smothering it — displacing the oxygen needed for combustion. CO2 extinguishers work well to douse engine fires on the ground, and are sometimes used in built-in engine fire suppression systems.

Unfortunately, CO2 extinguishers don't work well on cockpit fires. According to the National Fire Protection Association, a 32-percent concentration of CO2 is necessary to extinguish a gasoline fire — much more than is required to extinguish an air-breathing human. The extremely cold CO2 might work nicely to make a window brittle so you can escape the cockpit, but the cold shock can damage electrical components, and the particles and condensation can severely reduce cockpit visibility.

The best friend a pilot can have in the cockpit is a Halon extinguisher. Environmental concerns about ozone depletion and greenhouse warming have forced a ban on the production of Halon, but portable Halon 1211 extinguishers are still available, and will be until the present supply is exhausted. In the meantime, we can expect prices to rise.

Several characteristics of Halon make it attractive for fighting cockpit fires. Halon is a colorless gas that reacts chemically to extinguish fires. It works quickly, and at concentrations that are non-lethal to humans. Halon leaves no residue and doesn't damage sensitive electronic equipment. Halon is not as effective for fighting a deep-seated class A fire, but a quick-acting pilot can extinguish most cockpit fires using Halon.

Technique is everything

Having a fire extinguisher is only half the battle — when it comes to putting out a fire, technique is everything. A big problem, especially in class B (liquid fuel) fires, is flashback — flames from one part of the fire reignite the fuel that has been extinguished. The only way to avoid flashback is to extinguish the entire fire at once. To accomplish this, squeeze the extinguisher handles together and sweep back and forth across the flame bases as quickly as possible.


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