Fire Drill

Up in Smoke

September 1, 1986

Few things evoke panic like an aircraft fire in flight. We talk about training and practicing emergency procedures, but most are actually "abnormal procedures" easily handled by reading the check list. Not so with a fire. The pilot must know exactly what to do and why. He must understand the systems involved and have the critical procedures memorized. And these procedures will probably be accomplished while simultaneously executing an emergency descent because every second a fire burns, the flight moves closer to catastrophe.

Getting the fire stopped is the obvious first step. Just as obvious is the need to land somewhere quickly because in less than three minutes, the wing or engine mounts could burn off. Even if the fire appears out, you must land at the nearest suitable airport or other landing site because, as records show, the fire could restart. This is especially true of fuel line leaks. In fact, regulations require that you execute a forced landing quickly. According to FAR 91.29, the pilot "shall discontinue the flight when unairworthy mechanical or structural conditions occur."

Checklist procedures are guidelines to be used with common sense based on all factors relative to the situation. For example, in a single-engine aircraft, a tower report of a thin trail of smoke after takeoff implies either fire or possibly an unsecured oil dipstick. If it is indeed a fire, most check lists recommend mixture Off, followed by a forced landing straight ahead. But if you are climbing through 400 feet over an industrial park with no other indication of a malfunction, your sense of self-preservation urges you to leave the engine running until within gliding distance of a suitable landing site, preferably a nearby airport. An emergency landing is appropriate because even if the smoke is caused by a minor oil leak, you face a possible engine seizure.

During climb-out, the pilot reported an odd sound in his Aztec's engines. He checked for proper leaning. Then for no particular reason, he began to watch his left engine. Suddenly he was startled to see the cowl's blue paint begin to bubble and turn silver. "It was melting," he remarked later. Then he leaned forward and looked underneath the left nacelle. "There was a large orange fireball blowing like a blast furnace," he reported. After feathering the propeller and shut, ting off the fuel supply, the fire subsided. The result was a forced landing with minor injuries. The aircraft, however, was damaged beyond repair. Cause of the fire was a defective "O" ring in the fuel injection pivot valve.

In another instance, a corporate pilot flying a pressurized Navajo at Flight Level (FL) 240 (24,000 feet msl) had a fire in the right engine. He began an immediate descent while simultaneously shutting down the engine. As he passed through FL210, the fire appeared to have extinguished. Although only 14 nm from a major metropolitan airport, the pilot opted for vectors to a Piper dealership some 112 nm to the west and landed approximately 50 minutes later. The problem was traced to the turbocharger. While it is difficult to fault coolness under fire, as it were, that 50minute flight took place with an unknown amount of structural damage.

In another mishap, the pilot of an Aerostar departed Destin-Ft. Walton Beach Airport in Florida at night on an IFR flight plan. Although there was a 1,600-foot ceiling, visibility was seven miles with a light wind from 30 degrees at seven knots. Approximately one minute after passing through 700 feet agl, the pilot reported failure of his left engine. Witnesses saw the engine burning. The pilot declared an emergency and was cleared to land at Eglin AFB on Runway 12. The tower advised him he was less than a mile from the runway. Soon afterward, the tower said, "You're flying right over it now." From the transcript, the pilot appeared preoccupied with the failed engine because he seemed unsure of the airport's location. Minutes after the engine failure report, the left wing and engine separated. The airplane crashed one mile from the airport, killing all three occupants.

What causes engine fires?

FAA aircraft fire statistics for the period 1980 to 1984 reveal that engine fires were the most prevalent, followed closely by those in electrical systems. Most engine fires occurred during engine start, usually with a flooded or over-primed engine. (Pilot error was the most common cause of engine-start fires.) The statistics show that malfunctioning components and maintenance errors led the causes of in-flight fires. Maintenance errors ranged from such findings as "fuel line nut left finger tight" to "loose main fuel line to pump fittings." An improperly installed oil cooler caused an oil-fed fire when it leaked into a hot exhaust pipe. Exhaust systems and turbochargers were frequent causes of maintenance-error and component-failure fires. The high temperatures in turbochargers and other exhaust components make this equipment prone to causing fires. Aircraft designers should protect fuel and oil lines from exposure to these components. In some cases, limitations of space and construction make this a difficult task. The Aerostar fire described above originated in the turbocharger.

Aging, neglected components and accessories are leading causes of engine fires. Carburetors have caused fires in flight and during starting and taxiing. Other fires have been caused by cracked and leaking fuel lines, leaking or broken fuel flow meters and fuel lines, leaking exhaust manifold gaskets and broken or cracked exhaust pipes.

Cracked cylinders ranked high as a cause of engine fires. A Cessna U-206E was consumed by fire after a reworked (4,500-hour) cylinder head failed during cruise at 4,000 feet. The pilot heard a backfire sound accompanied by a partial power loss. All engine gauges read normal except that the fuel flow was low and fluctuating. Subsequently, smoke filled the cockpit, and the pilot landed in a small field. Although the aircraft burned, the pilot was uninjured. This fire originated from a broken fuel injector line to the blown cylinder.

In the case of fuel line leaks, the fuel flow gauge or fuel pressure indicator can forecast trouble. In climb or cruise flight, a sudden fluctuation and reduction in fuel flow or pressure is cause for vigilance. A serious fuel leak in a twin will be revealed by uneven fuel consumption. Even though an engine continues running normally, excessive fuel consumption, combined with a low or fluctuating fuel flow gauge, is indicative of a fuel system leak. If fire has not erupted, the fuel shutoff valve should be placed Off before you change airspeed or altitude. A change in airflow patterns can easily ignite a fire.

Shutting off the fuel selector allows the engine to consume the fuel remaining in the lines. The engine then stops without creating as much of a fire hazard. But reduce power first and change the airflow pattern, and the stage is set for an in-flight fire.

In cases where there is a fuel pressure loss and the engine continues running normally, some of the older operator's manuals recommend turning the fuel mixture control off first, followed by prop feathering. This will shut off the ignition source but will not stop a ruptured fuel line from pouring fuel into the nacelle. Thus, a serious fire potential remains. Most modem operating handbooks fail to address this emergency.

A rough engine followed by engine smoke or fire should be handled exactly as the owner's manual suggests. Most manuals recommend mixture Off first, followed by fuel selector Off. With a blown cylinder head, as with the Cessna 206 described above, this may have stopped the fire. However, this pilot was over inhospitable terrain, and with partial power available, reluctant to shut down the engine within gliding distance of a suitable field. Here again, he used his best judgment and walked away unharmed. In a twin, there is usually no reason to delay engine shutdown.

What is the procedure for electrical fires?

Unfortunately, some manufacturers do not publish electrical fire procedures. A few aircraft operating handbooks advise simply to reduce the electrical load to the minimum required and attempt to locate the source of the fire. Often, the recommended procedure involves pulling all circuit breakers, then resetting them one by one until the faulty circuit is isolated. You know which circuit is bad by smelling the odor of an electrical fire, or seeing smoke or other evidence. In other words, this procedure has the pilot recreating the original problem. While pilots should always follow the information in the pilot's operating handbook, this procedure may not always be adequate when dealing with serious electrical problems.

Some Transport category airplanes have a "load shed" procedure. In the Sabreliner 40/60, for example, the electrical fire procedure calls for both generators Off. This shuts off electrical power to nonessential equipment. Then, if the smoke or fire continues, you simply switch off the battery or electrical master. Then all electrical power is gone, and the fire should go out.

Some lightplanes certified under FAR 23 do not have procedures so simple. In procedures advising that the alternator or generator be shut down, the battery will continue supplying power to the electrical system-if only for a limited period of time. Many procedures then advise the dubious operation of flipping switches or pulling circuit breakers to identify the fault.

Instead, consider using a simple two step process. Send out a Mayday over 121.5 MHz (if flying VFR) or declare an emergency to air traffic control (if flying under IFR or in controlled airspace) and notify ATC that you will be incommunicado. Then turn alternators (generators) Off, and master (or battery) switch Off. (Magnetos remain On.)

This causes instant electrical failure, which should stop the fire. Of course, a flashlight is on board. Without one, a pilot using this procedure when flying at night or in instrument meteorological conditions would be in a truly desperate situation. Though FAR Part 91 does not require one, FAR Part 135.159 (which establishes equipment requirements for carrying passengers under VFR at night or under VFR over-the-top conditions) does. This rule specifies that the flashlight be powered by at least two D-cell batteries.

Notice that we have been using the words "should stop the fire." Once ignited, an electrical fire may continue even though the pilot has removed the initial source of ignition. Insulation, carpets and other combustible materials may continue to bum. This calls for a fire extinguisher, assuming that you have access to the affected area. Every pilot should be familiar with the proper procedures for using fire extinguishers and for eliminating smoke or fumes from the cabin. Most operating manuals recommend that cabin heat and air controls be closed until the fire extinguisher has been used. Then, the cabin air controls can be opened, which should purge the cabin of smoke and fumes. (More information on the use of fire extinguishers appears below.)

In instrument meteorological conditions, pilots using the two-step procedure will have to rely on pitot-static and vacuum-powered flight instruments. Some twin-engine airplanes have electrically driven flight directors on the pilot's instrument panel and vacuum-powered instruments on the copilot's side. This means the pilot will have to fly by reference to instruments that may not be easily visible or interpretable because of parallax caused by the pilot's less favorable viewing position.

The pilot experiencing an electrical fire must land at the nearest suitable site, preferably an airport.

How do you fight cabin fires?

Cabin fires come in a wide variety. Careless smoking was the cause of six percent of in-flight fires. I once witnessed a fluid-filled cigarette lighter burst into flames. An 8,000-foot pressure change had caused it to leak. When the passenger attempted to smoke, the lighter burst into a ball of flames. His quick-thinking seatmates saved the day.

Extinguishing a cabin fire is a problem. You want to avoid injuring the passengers, yet the fire must be stopped. While modem cabin interiors are somewhat flame resistant, a fire extinguisher is a necessity. Recent tests show that only fire extinguishers using the new Halon 1301 are completely safe, even in a pressurized cabin. Halon 1301 is only toxic in very high concentrations. Halon 1211 is equally good in extinguishing fires but is more toxic than 1301.

Dry chemical, carbon dioxide and water-based extinguishers have proven deleterious to both cabin occupants and the equipment they are meant to protect. Dry chemical is the worst offender since it can blind cabin occupants, foul electrical equipment and cause corrosion.

The National Fire Protection Association recommends that neither carbon dioxide nor dry chemical fire extinguishers be used in aircraft and states that water-type extinguishers have very limited effectiveness.

Smoke and fumes

All smoke in an aircraft should be considered toxic. In a pressurized cabin at high altitude, this means immediate use of the oxygen mask. In cabin-class twins and turboprops, that wool upholstery produces cyanide gas as it smolders. The polyvinyl trim or headliner and the plastic partitions produce phosgene gas, hydrochloric acid and a blinding black smoke. Battery fumes are occasionally present in both jets and other pressurized aircraft. The problem is usually an overheated battery.

A classic example of this type of hazard occurred at Austin, Texas, at Mueller Field. The commercial pilot, flying a Cessna 180, was observed trailing smoke after takeoff. The pilot notified the tower of a problem and reported that he was returning to land. A helicopter began following the Cessna and noted the smoke trail became heavier. The aircraft nosed over suddenly and dove into the ground. There was medical speculation that the pilot was dead before impact. The cause of the mishap was an excessively long emergency locator transmitter (ELT) coaxial cable that shorted out the master switch solenoid in the aft section of the fuselage. The resulting sparks ignited a flammable baggage-compartment separator, producing a large amount of toxic phosgene gas and black smoke.

In a Mitsubishi MU-2 electrical fire, the smoke was so dense that the pilot was unable to plug his oxygen mask into its receptacle. He had great difficulty seeing the instrument panel. Opening the cockpit vent only made matters worse, since the smoke originated in the aft cabin. The vent created suction through the cockpit, which drew the smoke past the pilot. A passenger, who also was without oxygen, removed the emergency escape hatch. Although the electrical fire continued, the smoke diminished to the point that the pilot could see well enough to make a forced landing. As we mentioned earlier, correctly performing the emergency procedure check list may not eliminate the smoke or fumes, but it is most important to shut off all the electrical power that started the fire.

In the case of an overheated battery, the only solution is to stop the battery from charging by turning the alternators off. If the airplane is pressurized, depressurize the cabin and have all occupants don their oxygen masks. As with any air contamination problem, the diluter or pressure-demand oxygen systems (if the airplane is equipped with them) should always be on with 100-percent selected. With a Normal rather than 100-percent setting, the system will mix cabin fumes with whatever oxygen is provided.

At altitudes above Flight Level 250, a minimum 10-minute supply of supplemental oxygen is required by FAR Part 91.32 (b)(i), in addition to the general rules governing oxygen use in flight above 12,500 feet msl. Above Flight Level 350, pilots are required to breathe oxygen at all times. In the case of two man crews, only one pilot is required to be on oxygen above Flight Level 350. As for passengers, each occupant must be provided with supplemental oxygen at cabin altitudes above 15,000 feet msl.

In a pressurized airplane, all occupants need pure oxygen. With the simple continuous-flow oxygen systems, the masks must be located and plugged into the receptacle. If the passengers have not been taught the procedure, it is unlikely they will have oxygen available. The pilot of a pressurized aircraft should have his mask connected at all times and the oxygen system armed; otherwise, as the MU-2 incident shows, in the panic of a cabin suddenly filled with dense smoke, it is unlikely that passengers will be able to gain access to their oxygen equipment.

One of the principal products of combustion is carbon monoxide (CO) gas. CO has an affinity for the blood component called hemoglobin, which transports oxygen through the body. Carbon monoxide adheres to hemoglobin and blocks the absorption of oxygen. Pilot incapacitation can result from inhaling even small quantities of CO.

Opening a door, escape hatch or cockpit storm window produces a low pressure area in the cabin. The cockpit window or vent will suck the smoke directly past the pilot's face. An open aft fuselage cabin door in some aircraft causes a rush of air into the cabin, which can make matters worse. In lightplanes, cracking the door creates low cabin pressure. The benefits of opening an emergency escape hatch vary with aircraft type, but in the MU-2 it saved the day.

In the Beechcraft King Air~ the cabin pressure regulator and safety vent valves are located on the aft cabin bulkhead. With this design, dumping cabin pressure routes fumes and smoke through the baggage compartment. In other pressurized airplanes, these valves are located in the cockpit, so depressurization brings fumes past the crew.

In unpressurized singles and light twins, smoke can sometimes be removed by opening the cabin air controls and air vents. If smoke intensifies, then air controls and vents should be closed, since they aid the fire. If an airplane has a fuel-fed cabin heater on fire, opening the vents may allow flames or smoke to enter the cabin. In some aircraft, lowering the gear and flaps can aggravate a cabin smoke problem. For example, the Cessna 31OR operating handbook recommends a delay in lowering the landing gear and flaps until the last minute to prevent cabin smoke from increasing.

Light, unpressurized aircraft often have nothing to protect the pilot or occupants from serious concentrations of cabin smoke. One solution is a military surplus gas mask. It can be donned in seconds and costs about $15.

Other points to remember

One of the prime reasons for knowing and understanding the aircraft systems is to handle normal and abnormal situations. Your check list provides recommendations for the most common situations, but it cannot provide pilot judgment under unusual circumstances. Training in a sophisticated simulator is valuable because the simulator helps reinforce knowledge of aircraft systems by safely exposing the pilot to various emergency situations. More simple training devices, without motion or visual displays, are great learning tools. A pilot will know he is up to speed when he knows by memory the basic steps in dealing with fires. Do not wait for an in-flight fire to begin your training in fire emergency procedures. Learn and stay proficient, perform thorough preflights (some fuel and oil leaks can be easily spotted), and plan ahead. With an in-flight fire, the clock is ticking.

John M Lowery, AOPA 258071, is an aviation safety consultant. He is a highly respected aviation writer and owns a Piper PA-28.