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Fire Prevention

szicree

Well Known Member
I've been following the ongoing thread about fire suppression and, like everybody else, am scared sh*tless about the prospect of an inflight fire. In the hope of preventing them from starting in the first place, I'd like to get a thread going where folks can share info about actual fires with DETAILS about how they started. We've all read stories about a fire from a "fuel leak" or "short circuit", but I'd really like to get some specific details about precisely what failed and how.
 
Fire causes

I've read quite a few NTSB reports, and the ones that have fires are often started by catastrophic failures of the engine. Here's an example:

http://www.rv8.ch/article.php?story=20030912223623939

Other causes I've read about are oil or fuel hoses:

  • coming loose
  • chafing against something and wearing through
  • coming untied and touching the exhaust pipe
  • fatigue cracking (aluminum fuel line or brake line)

As Paul mentioned in the other thread, a fire requires fuel, heat, and oxygen. Since the normal operation of our engines involves lots of oxygen (airflow) and lots of heat (exhaust pipes and cylinder heads, brake systems), the only solution we have to prevent fires is to ensure that there is never any fuel to get the fire started.

Easier said than done!
 
i've had to deal with in-flight smoke/burning smell, but no actual fire. had i not landed to investigate, it probably would've turned in to something. this came from a bird starting to nest in the heat exchange box. when the weather turned cold, the heat from the exhaust manifold is apparently hot enough to burn the straw that was in there. the really bad thing, is there is no way of preflighting this without removing the cowl, and the tube from the heat exchange to the cabin. the straw was charred, so there were the beginnings of a fire there. i did get met with fire trucks and filled out the form, but the simple fact of this story is...always use cowl plugs (and wherever else there's an access for birds, if your bird is kept outside in the summer time...this was a rental 172). so, no failures to report on this one, except someone before me didn't install the plugs, and i didn't preflight the heat exchange box. :rolleyes:
 
I had an in-flight fire a few years ago in a CH-53E. We were about halfway through a 3-hour flight, and the January cold at 7000ft MSL had finally had it's way with us (crew of four - two pilots, a crewchief and an aerial observer {me}), so we decided to crank up the cabin heater.

A little background - the cabin heater on the -53E is well-known in the fleet for being a stubborn system. It's great when it works (600,000 BTU's will get you warmed-up quick, even in Norway in February), but those times are somewhat rare, so it doesn't get used often. Anyhoo, there's 2 blowers in the system - a vent blower which moves the heated air from the plenum chamber to the cabin vents, and a combustion-air blower which (as you may have guessed) accelerates the air/fuel mixture into the plenum chamber for a good, hot burn. The fuel nozzle is mounted in the combustion-air blower's outlet port, which is V-band clamped to the plenum chamber.

So there we were... cold. The crewchief turned the heater on, and about 10 seconds later the pilots say "Hey, we've got a fire light!". At the same time they're saying this, smoke starts pouring in through the cabin & cockpit vents. In just a few seconds, the cabin and cockpit were full of smoke, and I could barely see well enough to get to the gunner's window on the left side of the cabin to open it (step 1 of the Emergency Procedure for "smoke and fume elimination in-flight" in the 53 - open all cabin windows and doors). As the crewchief and I were opening the windows, the copilot turned off the heater and the pilot made a MAYDAY call. Once we opened the gunner's window and the upper crew door, the smoke was swirling around a lot, enough that I could see what I was doing again. Smoke was still slowly coming through the vents, and the fire light was still lit in the APP/Heater T-handle (meaning the system was still detecting flames in the APP/heater compartment), so I pulled all the circuit breakers for the heater while the crewchief pulled the T-handle (the T-handle closes the firewall fuel valves for the APP and heater and discharges the fire bottle into the compartment). In about 10 seconds, the fire light went out. While I was pulling C/B's, the pilots dumped the collective to get us on the ground ASAP, and we basically auto-rotated through the descent even though we still had all 3 engines online. It's the fastest way down in a -53; at one point, I saw almost 6000FPM descent rate on the VSI... We landed in a farmer's field somewhere in MD and had to shut-down with no electrics (without the APP running, the generators drop off-line around 92-90% Nr, and there's currently no battery back-up for the electrical system in the -53) and no hydraulics (the pumps stop producing 3000psi for the systems at about 20% Nr). Finally safe-on-deck, but we've got no way to tell anyone - no battery means the aircraft radio's won't work, so we're NORDO. Hey, wait - we're all wearing our survival vests with an emergency radio - we've got FOUR comms! Well, that was the theory... reality was that 3 of the 4 had dead batteries, and the 4th wouldn't talk to anyone. But that's another story... One of the pilots had a cellphone with him, so he dug-up a number for whatever agency he had been talking to when he MAYDAY'd and called them to let them know we were safe. Meanwhile the crewchief and I opened up the "doghouse" (the cowling over the APP/heater compartment) to assess the damage, and the Coast Guard buzzed us a coule times in a Dauphin before they landed near us to talk to the pilots. About 10 minutes later, the farmer showed up. He was a little pissed that we landed in his stubble field, but as soon as I told him we'd had a fire in-flight and it was an emergency landing, his attitude did a 180. He brought us coffee & sandwiches, and offered us just about anything we wanted or needed. We assessed the damage and got another 53 headed our way with the parts we needed to "one-shot" our aircraft home. Swapped out an APP wiring harness and a fuel line, and we were on our way home. The aircraft was down for almost a month for investigation and repairs.

The cause of the fire was determined to be the combustion-air blower. The impeller shaft was seized in it's bearings, which caused the motor wiring to overheat and catch fire when we turned the heater on. The motor's windings also caught fire. I don't like to think too much about the proximity of the flames to the fuel nozzle and it's supply line, which had fuel being pumped through it at the time.
 
Lottery ticket

I hope you bought a lottery ticket on your way home - that was your lucky day!
 
A friend with a Glastar just returned from a trip and had an exhaust pipe break. He heard the sound change and thought it was just the exhaust tip coming loose. He then started feeling heat in the cabin but no smoke. He landed and found the broken exhaust was blasting heat right at the firewall. When the first pipe broke it left the crossover pipe unsupported so it broke next blasting heat right on a fuel line. We both believe the fire sleeve he installed on the fuel line helped keep a bad situation from becoming a disaster.
The exhaust was not stainless but was installed correctly. He is now putting a set of Vettermans stainless exhaust on the Glastar. There are many ways a fire can start in an engine compartment. I'm glad I still have my friend!
 
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