I still have my airplane today. And I’m very lucky I do. After the most recent annual inspection was completed, my aircraft’s induction system caught fire. I found I was woefully unprepared for such an event. If I was unprepared, you probably are, too.
Thankfully, no real damage was done. But this event highlighted for me some of the things we take for granted in our personal aircraft, as well as the fact we always need to be prepared for the unusual, and respond accordingly.
Before I share the details, I should explain the safety systems present on aircraft. One of the most important safety features is the firewall. The firewall, of course, separates the cabin from the engine compartment. It was developed to provide the pilot additional time to land and exit the aircraft in the event of an engine-compartment fire. In the early days of aviation, firewalls were made of wood, but that changed quickly. Modern aircraft usually have one made of stainless steel, which performs better in both slowing the spread of the fire from the engine compartment and providing an effective barrier to the heat generated by burning hydrocarbons.
To ensure the firewall’s effectiveness, it’s critical that all holes, no matter how small, are properly sealed and that any location where there needs to be an access, such as the engine controls, are of minimum practical size and then sealed with a fire-resistant grommet to a snug fit. There are three primary reasons for this extra care.
First, anywhere that fuel vapors can get to, a fire will follow. Second, in the event of an engine compartment fire, it’s critical to delay as long as possible any smoke entering the cockpit. Smoke in the cockpit is very bad news, making breathing difficult, impairing visibility and easily inducing panic among passengers and pilots alike. Smoke in the cockpit certainly will distract from the emergency procedures you should already be trying to implement.
The third factor is carbon monoxide (CO), a toxic gas produced by an internal combustion engine’s operation. This gas is odorless and colorless, and is very difficult to detect. Any small leaks in the exhaust system can allow CO to be present in the engine compartment, and from there it easily can enter the passenger compartment. In the event of breaching the firewall, it’s likely CO will enter the passenger compartment and affect the people within.
In flight, with the slipstream force-feeding oxygen, a fire likely will spread and intensify very quickly. The firewall is intended to provide a measure of protection. It may not be enough to get you to the nearest airport; we’re not talking long-term protection. So, it’s imperative that you put the airplane on the ground as quickly and safely as possible, get out and get as far away as possible as quickly as possible.
In referring to the checklist found in the Pilot’s Information Manual for my Socata TB20 Trinidad, the recommended responses for an in-flight engine fire are in the checklist excerpt reproduced at right.
As the checklist highlights, after identifying the fire, the first three steps are designed to stop the flow of fuel into the engine compartment. It is very important to set the fuel selector to OFF; most likely it isn’t in the engine compartment and, hopefully, won’t be affected by the fire. Next is the mixture control, which is attached to the carburetor or fuel-metering unit, and may have melted because of the fire. Get these OFF immediately to help prevent fuel from feeding the fire.
Also, in this aircraft, the cabin climate system has a fire cut-off setting. This is intended to keep the smoke out of the cabin. The documentation warns, “No attempt should be made to restart the engine after a fire.” Once the fire is out and the engine secured by switching the magneto selector and alternator field circuit breaker to OFF, execute a forced landing as instructed elsewhere.
Most aircraft I have flown (including mine) have not been equipped with a fire extinguisher. It wasn’t when this fire occurred, but I’ve since remedied that deficiency. When I had my induction fire, I found that I was wholly unprepared to do anything about it. All of my preparation and forethought was focused on a fire starting in-flight, not on the ground. I was literally contemplating fighting the fire with the shirt off my back. If it weren’t for the timely appearance of a fellow pilot, who had the foresight to install a fire extinguisher in his automobile—and the wisdom to deploy it in a timely manner—I don’t know if my airplane would be airworthy or the charred property of the insurance company. I will forever be indebted to him.
Which brings me to: As a member of the flight and airport community, if you see something amiss with an aircraft, get involved. It is very difficult to shift focus outside of dealing with the emergency at hand and looking for someone to help when you need it. But, I assure you, any and all help is very welcome, even when all you can offer is to call 911.
Lastly, be vigilant for any signs of blue stains on or around your engine. Anytime you see one, it’s a sure indication there has been a fuel leak. It is very important to determine how it got there.
This year, during the annual inspection, my aircraft was lubricated in accordance with the maintenance manual. This includes lubricating the fuel-metering unit, where the throttle and mixture cables connect. The manual’s instructions are to lube the cables and connections, then exercise them (with the engine off) to ensure oil travels up the cable housings and lubricates them.
Other tasks accomplished during the annual inspection included cleaning the fuel injectors, performing a 500-hour inspection on the magnetos and complying with an AD mandating inspection of the fuel lines. As part of the normal process, the engine is started to ensure there are no problems after reassembly. The TB20’s cowl is split into an upper and lower half. The upper half was removed for the service; the lower cowl remained installed.
The engine priming procedure calls for the throttle to be opened ¼ of an inch, the fuel pump to be turned on and the mixture to be moved from the idle cut-off position to full-rich position for 4-7 seconds, then returned to idle cut-off. Unfortunately, I was distracted with some other task during this process. The result was the mixture control was in the full-rich position throughout, resulting in several more seconds of priming.
When the engine fired, excess fuel in the induction system ignited, causing the air filter to catch fire. The air filter is a spongy material impregnated with oil to trap particulate matter before it gets into the engine. When the air filter caught fire, it burned with a white smoke, which drifted aft and above the uncowled engine. This was the only clue there was anything wrong. In fact, in talking with other pilots who had experienced induction fires, it is very likely a pilot will not know they had one until the event is over.
In my case, I did realize there was a problem, but the presented symptoms did not indicate an induction-system fire. If I had correctly identified the problem, the checklist instructs me to set the mixture to idle cut-off and engage the starter for no more than 10 seconds, then move the throttle to the full-open position and turn the fuel selector to OFF. These steps would have deprived the fire of any further fuel by stopping it from flowing into the engine compartment while attempting to suck existing fuel and the fire itself into the engine.
At the time, I thought some of the lubrication I had just applied had ignited, or perhaps that I had damaged the fuel lines. In any event, when I did look into the engine compartment, I noticed an orange flame coming from the air filter area. At that time, I began removing the lower cowling and attacked the 12 fasteners holding it on. I was attempting to get better access to the fire, but I also recognized the risk posed by introducing more oxygen to it. It was a toss-up. I don’t know if it was the right or wrong decision, but in the heat of the moment, it was my plan of action. At the end of the day, it’s better to follow through on some plan until it’s clear it is the wrong choice than sit and do nothing while weighing options.
During my efforts to remove the cowl, a fellow pilot stopped by and asked if I needed any help. I gratefully accepted his offer, in the form of the fire extinguisher he had with him.
In retrospect, I think I was very naïve when it comes to the possibility of an engine fire. Since my very first flight, I have been a careful, safety-conscious pilot who put a lot of time and energy into being trained and prepared to deal with what I thought were all the common aviation emergencies. I always thought this sort of thing was something that happened to other people. People who were not as smart as me or as prepared, or who were just plain unlucky. I didn’t understand the details and the visible signs of what was going to happen. I was not prepared when it happened to me.
Most pilots will go their entire flying career and never have an engine fire. If you do, I hope you see something in my experience that helps you. It’s good to learn from your experiences, and it’s even better to take the opportunity to learn from someone else’s.
James Warmkessel holds FAA flight instructor and A&P certificates, and is an aviation podcaster and IT professional living in the San Francisco Bay Area. Follow his podcast at www.avstry.com