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


_________________________
* 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).

[hharney]

Really good stuff Ernie

Here are a couple other thoughts, and a good reason to attend SOAPA meetings. Install a heat detector in the cowl of the rear engine. it is monitored by a warning light on the panel. This will provide an advanced warning.

Also, I just installed a mirror on the inside right boom just ahead of the interior flap. This provides some nice views of the right side of the rear engine. I can see the prop when I start and the cowl flap. Not sure it would be the best for a fire on the left side but maybe you could put one on the left boom too. A small rectangular convex mirror would work best.

And lastly, attend SOAPA. In Branson, MO at the 2009 meeting we had Capt. Dennis who had experienced a engine fire over water and he had some emergency gear to demonstrate. Here is a photo of a smoke hood and life jacket. The cheap little cellophane bags that you put over your head are worthless so get one like in the photo at the least.

And we had to learn how to use the raft if you went into the water. Good practical stuff and only at SOAPA.

[skymstr02]

We O-2 owners have the luxury of having a fire detector system installed on our rear engine compartments. There are four fire detectors set at 350F that will illuminate a red light on the panel when the compartment temp reaches that threshold.

[Dale Campbell]

I had a undected leak in rear muffler and the A/P did not even find it during annual. I found it! He was about to put the cowl back on when he finished the annual, when I was there and I noticed a white calky film on oil pan co-pilot side on rear engine. I got a flash light and found a hole 4 inches long and 1/8 inch wide right next to outside rib on muffler. You had to look hard to see it. So I would tell every one to check that rear muffler real good every time the cowl is off and watch for that calky film that is the key to exhaust leaks. the scary thing is the gas lines to the engine primer is right there above were the exhaust leak was and if there was any sign of gas leak, puff I would not be here. Dale Campbell

[jchronic]

I very much share the concern about rear-engine fires and posted a question on the subject awhile back. So, glad to see the excellent suggestions from Ernie, and good input from others. My little aerial survey operation had to meet Part 135 standards for our primary contract and here's how I addressed in-flight fires in my ops manual:

IV.4 Inflight Fire: In the event of an inflight fire, immediately head toward a suitable landing site – which may not necessarily be an airport. Accident history clearly shows that an inflight fire can quickly incapacitate the crew and/or render the aircraft uncontrollable. A safe landing as soon as possible – even off airport - is of critical importance in surviving a fire inflight. Non-pilot crewmembers/ passengers should attempt to locate the source of the fire (if in the cabin) and take steps to fight it. After landing, cease firefighting efforts and immediately exit the aircraft.

I also invested in smoke-hoods for myself and my crew. One experience with a smoke-filled cockpit was enough to make a believer out of me.

When I was a check airman at the airlines, I used to ask in the briefings what was the first thing to do in the event of a suspected fire. The answer usually came back "Get the checklist out," and my response was "No, that's second; first thing is to turn immediately toward a suitable landing site and descend. Getting on the ground quickly and safely is everything."

Joe

[Roger]

These messages as related to exhaust leaks (which can among other things cause fires) interest me because I haven't YET had any rear exhaust problems. But I almost did.

I consider my aircraft to be pretty well maintained, yet at the last annual the A&P noted something that had essentially been overlooked for perhaps some time. The two holes in the rear cowling where the exhast pipes come out, had small wear marks in the bottom.

The exhaust pipes were well above those marks, so it wasn't like they were rubbing on the bottom of the holes (while on the ground). But if you put a lot of weight on the spinner you could see the engine go down to a point where the pipes were getting close to hitting the bottom of the holes.

So we decided to measure the distance between the bottom of the pipes and the bottom of the holes, and then replace the motor mounts. The net result was that the motor is now raised about 5/8" at static, and the aircraft is much smoother in flight.

Essentially the rubber in the motor mounts had deteriorated to some degree (probably softened) and it allowed the engines to move around a bit (and enough to allow the exhaust pipes to hit the edge of the cowling holes). I can't help but feel that this type of movement and rubbing on the cowling in flight could cause cracks in the exhaust.

So I might recommend that everyone check this by just looking at the exhaust pipe holes in the rear cowling.

[jchronic]

So to ask the specific question: Does anyone know of an off-the-shelf fire or heat detector system suitable for installation in the 337 rear engine nacelle - either STCed or likely acceptable to the feds via form 337? Is the O2 system suitable (if one could be obtained)?

Joe

[WebMaster]

Do a search, and you will find this.

http://www.337skymaster.com/messages...e+extinguisher

[jchronic]

Larry -

Thanks. I think we may have had this conversation when I inquired before. One responder in the thread you referenced has extinguishers, and the guy with the O2 has a detector system. I'm less interested in an extinguisher than in a detector system, and whether anyone is aware of a system that be can put in a straight 337. I'd assume the O2 system could be adapted (or probably even be a straight drop-in), but are any even available?

Joe

[Skymaster337B]

Ernie, I'm curious about the "data of in-flight fires" you mentioned? I haven't heard of any Skymasters with rear engine fires, especially that ended in disaster.

It certainly would be nice to have a fire detector on the rear engine, but I can't image that Cessna didn't consider this. Maybe fire can't be sustained at normal cruise speed because of all the air going thru that rather large air scoop on top of the fuselage. Or maybe air flow is reversed (as it does in so many unpressurized cabins) that you would smell a fire. I guess we need to hear from some one who actually had a rear engine fire...and what they experienced. Don't get me wrong, extra safety equipment is nice to have, but let's not scare the crew.

[hharney]

Returning from the Bahamas in 2007, we had just attended the SOAPA event. Larry and I were flying with Jerry in his G model P337. We were on the first domestic leg from Ft. Pierce to a small airport in Southern Kentucky (can't remember the name now). I was in the rear and I was hearing some kind of knock or something. I had mentioned that I thought I heard something but Larry and Jerry didn't seem to hear it yet. Again, we are at Flt Level 100, we all have headsets on, in one of those noisy Skymasters and it's a pressurized cabin. I am hearing some kind of noise that is coming from the rear or bottom of the plane.

All of a sudden a loud quick knock gets the attention of everyone in the cabin. See I told you I heard something, I thought. Within a few seconds I could smell oil, burnt oil or hot oil. Jerry immediately called center and said that we needed down now. Center told us that Athens, GA was just a few miles on right and told us to squawk 1200 and call Athens. Ok, just drop us then. Anyway, one of the bolts for the rocker arm broke and the rocker made a hole in the cover. You will have to search the SOAPA Bahamas thread to see the photos and story about the amazing repair that day, in Athens, on a Saturday.

You can definitely smell hot stuff in the rear engine from the back seat, right away. We had no fire,

[Ernie Martin]

No, there is no data on any fire in the rear-engine compartment of a Skymaster. My research was generally about in-flight fires in GA aircraft, with two noteworthy findings: how little time between first hint and unrecoverable condition (average 7 minutes), and that the more likely location for a fire in older aircraft is in the wiring behind the panel (hence my suggestions on smoke masks and halon extnguishers).

The points made above that air flow in the compartment may preclude fires is interesting and worth pursuing. Maybe there is no cause for my concern about a raging fire while you keep on flying. The fact that Cessna added fire detection on O2s but failed to incorporate it on subsequent 337 models (G and H) may suggest that Cessna did not deem a fire a likely event in non-combat conditions -- after all, the design was done, so adding it would have had little impact on cost or weight.

Ernie

[Guy Paris]

Gentlemen, what is the consensus,
what would be the best kind of mask to get?

Guy, the old 72 driver....

[jchronic]

Guy -

I purchased four of the PARAT C hoods from Aircraft Spruce at about $150 each. Not cheap and I think there are others at less cost (and less capability). I got them for my whole survey crew, but my feeling is that there should be at least one on board so the pilot can get the plane down.

BTW, my neighbor George Breen, your old airline colleague said to say hello if we ever 'talked' on the web site.

Best regards -
Joe Chronic

[Guy Paris]

Joe,

Small world, say hello to George for me and thanks for the info on the PARAT C hoods.
Were you in at the Falmouth Air park recently? My daughter said there was a Skymaster
in warbird paint there recently.

Keep the blue side up, Guy....