According to a recent study, the elapsed time between the first indications of a hidden fire and the point at which an airliner becomes catastrophically uncontrollable has ranged between seven and 35 minutes. The average time is about 20 minutes. Twenty minutes is a long time, but the bad news is that those occurrences involved airliners. Things happen a good bit faster inside smaller aircraft.
THE DIFFERENCE IS WHAT COUNTS
In-flight fires, especially those in which the fire is not accessible, have resulted in catastrophic failure and the complete loss of the aircraft. A recent paper on the subject estimates that for transport category aircraft with hidden fires, only one third will reach an airfield before the fire becomes uncontrollable. (The good news is that for most of our general aviation airplanes, we don’t really need an airfield, if the situation starts heating up.)
Causes: There are the obvious ones, and then, the not-so-obvious ones:
- Fuel or other flammable fluid leaking onto a heated surface (such as the exhaust system) from broken hoses or lines, or in contact with a source of flame
- Many in-flight fires are caused by electrical arcing within wire bundles, exacerbated by flashover of accumulated exterior contamination from dirt, lubricants, or corrosion inhibitors. A phenomenon called “arc tracking” also can occur when a conductive carbon path is formed across an insulating surface. Fire can also be initiated by overheating when a tripped circuit breaker is reset.
- Overheating or otherwise failing electrical motors
- Lightning strikes (faulty or contaminated insulation is often involved)
- Faulty circuit breakers
- Cost-cutting maintenance or the use of non-standard parts or configurations.
POSSIBLE INDICATIONS OF A DEVELOPING FIRE:
- Odors: This is often one of the first signs of an impending fire.
- Smoke: another sign of an immediate problem
- Component failure: Whenever anything exhibits un-commanded operation
- Fuel flow: On fuel-injected engines, a sudden drop in flow
- Tripped breakers, especially multiple circuit breakers at once
- Hot spots (yeah, I know; “Oh, really?“)
- Electromagnetic interference (if something is frying, you might actually hear it in the headset!)
Options, actions, and things to remember
- Unwavering fastidious maintenance and scrupulous inspection. Then, the rest becomes only fate…
- Take immediate and aggressive action; declare an emergency, and descend. Delaying even by two minutes (and that time applies to airliners) has proved to make the difference between a rushed but successful landing and a total loss of airplane, passengers, and crew.
- If you think the fire is airframe or engine related, turn off the fuel. If it is electrical, turn off the master (and alternator) switch.
- Always know where your fire extinguisher is located. Review the classes of fire extinguisher types. You may think it’s trivial, but it isn’t, really.
- If flames are visible, fight the fire immediately. If they aren’t, do everything you can to find the source of the fire.
WHAT NOT TO DO
- Never ignore a strange odor (and obviously, you won’t ignore smoke)
- Never reset popped circuit breakers a second time, or even a first unless specifically required for safe flight. Circuit breakers are slow acting devices, and may not provide a quick enough compensation in cases of arc tracking or contamination flashover.
HOW TO FIGHT THE FIRE
If you have an actual cockpit fire and you somehow can’t get to the fire extinguisher fast enough, other things can be used as stopgap measures while you or your passengers prepare to get out the heavy artillery. When a fire is discovered, your focus should be on extinguishing the fire and then following up, rather than delaying your efforts while you search around for the Halon. Non-alcoholic beverages can be used on carpeting (warning: no water-based extinguishers should ever be discharged into electrical panels, or any grease or fuel fire on a non-porous surface). A carbonated beverage can, shaken and then opened so that its contents are sprayed at the base of a fire, may be used in a pinch. (However, Halon is three times as effective as carbon dioxide.) Blankets or pillows can be used to smother a fire (though possible out-gassing of synthetic materials from a confrontation with an intense fire could make things worse)
In the heat of the moment, always remember that handheld fire extinguishers are designed with a central siphon tube extending to the bottom of the canister in order to collect as much of the contents as possible from that point. Thus, they are meant to be operated while being held in the upright position. Holding them sideways or turning one upside down to aim under the control panel for example will drastically reduce its fire-fighting capacity.
Remember Firefighting 101: attack the base of the fire at the near edge first, rapidly sweeping back and forth and progressing towards the back of the fire. Also remember that the effective duration of most small handheld extinguishers is only eight to (at most) 25 seconds. Time counts.
Ventilating the cockpit after discharging the entire contents of an extinguisher is a good idea (unless the fire isn’t out). This reduces exposure to gases produced by thermal decomposition. And according to the NTSB, “…the potential harmful effects on passengers and crew are negligible compared to the safety benefits achieved by fighting in-flight fires aggressively.” That said, however… If a cockpit or instrument panel fire has not been extinguished, there is the irony that your attempts to ventilate the cockpit of smoke and fumes may also provide air for the situation to continue or become worse. Whenever possible, extinguish the fire, first.
A little-known fact: the best way to locate a hot spot on any surface or panel before attempting to open or remove it is not with your outstretched fingers or palm, but by using the back of your hand. The back of the hand is actually more sensitive to temperature variations, and it will allow you to protect your palm and fingers from potentially being immobilized, which would obviously impair your being able to conduct fire-fighting activity or evacuating passengers.
WHAT ‘THEY’ SAY
Some authorities give fairly sensible advice that once you’ve vanquished the fire or smoke, you should carefully reset the electrical system, as recommended in the POH. The procedures usually say to keep the avionics master and all other accessory switches off, and turn the master on first, then the alternator, and then to bring subsystems back on line, one at a time. Me, I’m going to land, pronto, and get an A&P to look at it later … supposing that there is a “later.”
THE BOTTOM LINE: I know you may rightly think that this is easy for me to say, but the main thing to remember is that if you ever do suddenly find yourself in the skywriting business, or if you get the hot foot, keep a cool head. As much as the thought of an in-flight fire may strike terror into a pilot’s soul, an in-flight airframe failure will make any pilot shudder, equally well. The fact is that in most accidents, the pilot is either overcome by smoke (which admittedly one can’t do as much about) or panics and loses control of the aircraft.
