An in-flight fire is one of the scariest and most serious emergencies a pilot can face. Smoke and heat can quickly incapacitate the pilot or make it difficult to see the instrument panel or to see outside of the airplane. Fire can also damage critical flight instruments. Attempting to vent smoke by opening a window or door can make things worse by supplying the fire with additional oxygen. A pilot may only have several minutes to get the airplane on the ground after a fire has started. In-flight fires are bad news. It's for these reasons that we need to do everything within our power to minimize the chances of starting an in-flight fire.
If I asked the average General Aviation pilot what he'd do if a circuit breaker popped in flight, he'd probably give me the typical response that he'd reset the breaker once and if it popped out again, he'd leave it alone. Most light airplane pilots are familiar with this protocol. That's not necessarily the best idea, though.
In January of 2004 the FAA issued an Advisory Circular (AC), AC120-80, "In-Flight Fires," in response to several in-flight fire-related accidents including the crash of a Swissair MD-11. The AC was widely distributed throughout the air carrier community, but not throughout the General Aviation community. The AC provides guidance on responding to tripped circuit breakers in-flight. Airline crews now use procedures that discourage (or prohibit) resetting a tripped circuit breaker in-flight unless the breaker corresponds to an essential electrical component. Many jets have an "essential" electrical bus and a "non-essential" electrical bus. Non-essential breakers typically are not reset even once during flight unless absolutely required to maintain safety of flight. Essential breakers may be reset minimally per company guidelines. But, why am I talking about circuit breakers?
Electrical fires have occurred because a defect in the electrical system (malfunctioning electrical component, faulty wiring, etcetera) prompted a circuit breaker trip and the crew reset the breaker, perhaps multiple times, until a fire eventually started. So, the idea is that when a circuit breaker pops it usually does so for a good reason, so resetting it must be done with caution and only if necessary for continued safety of flight. Occasionally a transient event will pop a breaker, though, so resetting a breaker once is not necessarily a reckless thing to do. It just depends. The airlines have an excellent system in place for dealing with tripped breakers, and so can us GA guys.
Though we can't rearrange our circuit breaker panels into essential and non-essential breaker head clusters, we do have other options for organizing them. One excellent strategy is to use color-coded breaker bands to distinguish between essential and non-essential breakers. If you rent airplanes like I do, this might not be possible. The solution then becomes to rely on your memory to know which breakers you can reset once and which ones must be left alone in-flight. Luckily, this isn't extra difficult to memorize because light airplanes don't have nearly as many breakers as larger, more complex airplanes. Start by referring to the airplane's Pilot's Operating Handbook (POH) to determine what the manufacturer recommends on resetting popped circuit breakers. This is always the best starting point for systems guidance because no one knows the airplane better than the folks who designed and built it, so their word supersedes all other recommendations. Where POH guidance lacks, though, universal rules-of-thumb can pick up the slack and provide useful solutions. By combining POH guidance with some general know-how you should be able to determine which breakers may be reset in-flight and which ones to leave alone. Even if an essential breaker pops, it should only be reset after the pilot has confirmed that the corresponding electrical component isn't obviously malfunctioning (i.e. the turn coordinator appears to be smoking). Also understand that should an in-flight fire begin, you might not be able to make it to an airport. It's quite possible that an off-airport landing is your best bet. The name of the game is to get the airplane on the ground in the shortest possible time after detecting an in-flight fire. Remember, you may only have a few minutes. The instant you suspect a fire has started start looking for the nearest suitable landing spot.
You can also limit your exposure to the risk of an in-flight fire by never flying an airplane that has an unresolved electrical system squawk. One common example of this would be to refuse a rental airplane that has a failed electrical component that hasn't been placarded "Inoperative" and doesn't have the corresponding circuit breaker collared. There's a reason that placard is required by the regulations, and there has been at least once accident that I know of that resulted from an airborne weather radar that had a known malfunction yet hadn't been placarded inoperative nor had its circuit breaker been collared. Anytime an electrical component has malfunctioned on a recent flight the airplane should be inspected by a mechanic before the airplane returns to service.
To summarize, never reset a circuit breaker in-flight unless the corresponding electrical component is absolutely critical to the continued safety of the flight. When flying VFR during daytime in good weather, this could easily mean there's not a single circuit breaker that should be reset. When flying IFR in low weather, a number of breakers might be considered essential for safety of flight and would be necessary to reset. Above all else, follow the specific guidance and recommendations contained in the aircraft's POH. Remember to always bring a couple trustworthy flashlights (I passionately recommend SureFire products) for night flights, too. I once flew a Piper Cherokee on a cross-country flight over the Great Plains at night with no electrical power. The cockpit was as dark as the night and all I had was a flashlight to provide occasional glances at the magnetic compass; the rest of the panel was unusable. Luckily, this was only a training exercise during my commercial pilot training. And aside from a map being draped over the instrument panel to test my pilot improvisational skills, this situation can occur and a flashlight becomes a rather critical piece of equipment.
I'm not easily scared as a pilot. But the thought of an in-flight fire is particularly frightening to me, as it is for many pilots. We can drastically reduce our chances of ever encountering this dreadful emergency by using intelligent procedures and preparing ourselves so that we can respond immediately and properly if faced with an in-flight fire. The recommendations I've provided here are inspired by FAA AC120-80, and when they are used they will greatly reduce your chances of ever meeting with an in-flight fire.
