In-Flight Fire – Maybe in the Rear Engine You Can’t See

[Ernie Martin]

A recent development led me to look into in-flight fires, with initial emphasis on one originating in the rear engine compartment.

I know it’s a scary subject and highly unlikely to occur, but I suggest that you will find my findings of interest because a) some of the data is enlightening, and b) several simple and inexpensive measures can mitigate the risks.

It all started with the surprising discovery of a crack in one of the rear-engine exhaust pipes. Two months earlier, at annual inspection, the exhaust system had been deemed airworthy “for the time being”, with a warning that it would probably need replacing within a year. That gnawed at me. Might it fail in flight before the year? Might it lead to a fire that rages back there while I continue to fly?

Let me make a quick detour to remind you that the most effective way to deal with an in-flight fire is to act at the slightest hint (e.g., the first sight or whiff of something burning), start an emergency rapid descent, and put the aircraft on the ground. The data suggest that you have an average of 7 minutes from first hint to an unrecoverable condition (e.g., pilot incapacitation, structural failure).

You can see the source of my concern. With a rear-engine fire, it might take most of those 7 minutes before I even know there’s a fire.

So rather than wait, I hired a more experienced mechanic/inspector for a thorough look. He not only found the crack in one of the risers (the exhaust pipe that attaches to the cylinder and therefore gets the hottest flame), but when we removed the risers we found substantial erosion on the exhaust flange of two cylinders, indicating two other places where exhaust flames might have soon escaped into the engine compartment.

While I waited for the exhaust system to be overhauled ($ ouch, and a story in itself, with prices and results all over the map) I looked at the data on in-flight fires that is the basis for the material which follows.

On the rear engine I have three suggestions. First, have your mechanic and/or IA do a careful visual inspection of your rear engine exhaust, fuel and oil lines, not just at annual, but every time he works on the aircraft. He changes a tire, have him inspect. He changes the oil, have him inspect. It’ll only add 15 minutes to the job, including removing/replacing the cowlings. Best 20 bucks you ever spent.

Second, while I would love to add an automated Halon fire suppression system, the cost, weight and STC ramifications are prohibitive for most of us. However, a tiny video camera in the engine compartment feeding a small screen mounted on the panel may be an inexpensive compromise, one that I raise here in the hopes that an electronics hobbyist among our group might want to pursue and share.*
Third, I have adjusted slightly the angle of the mirror I have under each wing so I can now see the rear engine as well as the landing gear (with the correct wide-angle mirror, you can still see the nose gear). I am getting in the habit of looking to the rear engine on roughly every fifth instrument scan.

More generally, I also honed my procedures to deal with in-flight fires, not just engine fires but the more common occurrence on older aircraft of an electrical fire, often in the maze of wires behind the panel. What follows is highly abbreviated; far more comprehensive papers may be found on the Internet.

The drill is in three (3) steps:

1. Immediate rapid descent – i.e., put it on the ground ASAP.
2. Emergency call on the radio describing situation and position.
3. Take mitigating actions.

Step 1 is typically done with both the gear and flaps down and the throttles closed. Step 3 involves turning off the master and alternator switches if it’s an electrical fire; shutting off fuel to the engine if it’s an engine fire; and attempting to put out the fire if it’s in the cabin or behind the panel, and if you have a fire extinguisher, and if you (or a passenger) can do that while maintaining positive control of the aircraft.

As a result of looking at accident data from in-flight fires, I have taken two measures that I want to share for your consideration.

First, I’m replacing my powder-type ABC fire extinguisher with a Halon unit. In part because I learned that it is far more effective than my old one and in part because Halon extinguishers are still affordable (small units around $100 online). Operative word here is “still”. Because of environmental issues Halon is no longer manufactured for fire control, and all new extinguishers are filled with reclaimed Halon (typically from large industrial devices); as the supply diminishes, prices will go up, and eventually they won’t be available.

Second, I have bought four smoke emergency masks to try to prevent incapacitation and/or eye impairments, something which happened in many of the accidents. This is a transparent bag with an air filter that fits over your head, with a rubber band making a snug fit around your neck. It filters toxic chemicals and smoke, giving you roughly 15 minutes of air. I opted for the Breath of Life mask sold by Technon online (www.technonllc.com) because of the price ($35 each, or $31.50 with the family discount if you buy four and order by phone) and its tiny size (a 6” by 6” nearly flat foil pouch). This unit does not filter out carbon monoxide (CO) but I deemed it satisfactory for my kind of flying (where I’m typically under 6,500 feet altitude, over water, and can put it down in under 5 minutes). For those of you who fly higher or may want to protect against a longer-burning fire, where the prospects of CO increases, bulkier and more expensive masks that filter out CO and have greater heat resistance can be found at Sporty’s, Aircraft Spruce and elsewhere; one of these for the pilot and several of the ones I bought for passengers may be a sound compromise.**

Hope some of this was helpful.

Ernie


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* I see in auto parts stores similar systems sold for well under $100 so drivers can see behind their cars when they reverse. If such a system was self-contained, with, say, AA batteries providing power, I would not hesitate to install it in my airplane without an STC.

** An interesting alternative for the pilot, with extreme protection for a mere $20, is a surplus Israeli gas mask. These are in pristine condition, with a new filter, available online at Amazon. They are, however, far bulkier (half a shoebox?) and take longer to don (the mask and filter are in separate sealed bags and need to be joined).