Imagine my thoughts after doing some electrical wiring clean-up under my panel, and quite carefully, I turned on the Master Switch one day before the first post-work flight and the cabin filled immediately with acrid smoke. An wire wrapped EGT probe wire was very close to the exposed ammeter shunt, and (actually luckily) at some point while cleaning up after the work I must’ve bumped it into contact. The amount of smoke produced before I could shut off the Master was phenomenal – and nothing was even damaged. Having looked everything over, the A&P and I then tied it back so that it will never, ever happen again! He did it and then asked me to inspect it.
It was not a nice thing to contemplate that occurring in flight.
Fire and more especially an electrical fire is the only thing in aviation that really scares me, the A320 fire/ fumes check list go around in circles ( the B737 one is a bit better ) but basically the drill is to try and isolate the bus bar or service that you suspect is giving trouble while the other guy is getting the aircraft on the ground ASAP.
The cabin crew are trained in the use of the extinguishers and if they suspect a fire from behind an internal panel to smash a small hole and empty a halon extinguisher into it.
Halon is an incredible extinguishing agent, in the days when we could train with it I attempted to put out a trough of burning fuel with a 5kg CO2 extinguisher, it could be done but only if you worked slowly from the upwind end, the same fire was extinguished with a quick squirt of halon from a downwind position, however I would think that in a small cockpit it is most likely to expel the oxygen that you need to breathe.
With the belief that prevention is better than cure my current DR400 rebuild project includes all the 1970’s French car electrical cable being replaced with aviation grade cable, I can only describe the rats nest of old car wiring being an electrical fire waiting to happen, not so bad if your VFR mission enables you to turn off the battery and land in a field but IFR or night this is not an option.
Aviathor wrote:
And as we do not have oxygen masks in our airplanes, a halon extinguisher should not be discharged in closed quarters (i.e. in-flight)
Better inhaling toxic stuff for a minute than burning to death… On a non-pressurised aeroplane you can always open the storm window (or side window in any Cessna) or open the door for fresh air.
And as we do not have oxygen masks in our airplanes, a halon extinguisher should not be discharged in closed quarters (i.e. in-flight)
Aviathor wrote:
If it suffocates the flames, I do not even dare think it will do to a human. Not sure it will do any good unless you are wearing an oxygen mask.
Yes. This is why “Oxygen mask – don” is the number one item of all fire and smoke checklists I have ever seen. The working principle of Halon goes beyond suffocating the flames – here is something everyone should have read before using it (almost all small handheld extinguishers found on aircraft are of the Halon type!): http://www.skybrary.aero/index.php/Halon_Fire_Extinguishers
If it suffocates the flames, I do not even dare think it will do to a human. Not sure it will do any good unless you are wearing an oxygen mask.
Peter wrote:
If you just see smoke coming out of something, would poking the extinguisher “in there” be any good?
From what I have been told in our regular firefighting courses I would say no. The only good it could do would be to cool the overheated wire (after the current has been removed otherwise it would be useless!) below the point of generating smoke. The extinguishers mostly used in aircraft are filled with Halon however. This gas does not provide much cooling, instead it basically suffocates the flames. Without flames, there is nothing a Halon extinguisher can do. With a CO2 or water extinguisher it would be different, but one usually does not carry that on board.
I wonder whether a fire extinguisher is useful unless you can see flames. If you just see smoke coming out of something, would poking the extinguisher “in there” be any good?
Peter wrote:
What happened?
In the cruise over North Devon, FL180 or thereabouts, just 2 of us on the aircraft having dropped off my parents at Newquay. Good weather above a broken cloudbase with good vis beneath
A slightly woody smell appeared, and my colleague in the right seat, who is much more experienced than I, went down the back to see if it was a fault with the Mapco (electric hot water container). It wasn’t, but looking down the aircraft from the back a wispy flow of smoke was coming up from my foot well area.
We decided a diversion to Cardiff was in order and called a Mayday, and requested a diversion. A decent towards Cardiff was started and we decided that as the smoke was clearly electrical we would switch off the Battery and take both Generators off line. We later switched on the one hot wired radio via the Clearance/Delivery button on the panel.
In the descent we de-pressurised and opened the clear vision panel and the smoke started to diminish.
We landed flapless at Cardiff, and by this time the smoke was almost gone, however despite our protestations they followed procedure and insisted we stopped and evacuated on the runway, which we did, surrounded by fire appliances.
After more than one inspection by a fireman with a thermal imaging camera it was decided the hot area, which was under the pilot’s feet, was cooling, and the fire chief asked if we would taxi the aircraft off the runway. I declined as we would all have looked a bit daft if the thing had caught fire as we switched on the battery and then taken several hundred amps to start the engines!
They couldn’t find a tow truck that would work and so we were pushed off the runway by the combined efforts of all the fire crews.
The fault was later found to be with the cabin air blower. Had we followed the check list to the letter rather than our decision to switch off all electrics the check list called for “cabin air blower – HIGH”, which in this case would have made things worse.
If the weather had been worse we could have been in serious trouble. I seem to remember that the offending blower motor apparently once had a requirement for service every 1000 hrs, but this was discontinued; our aircraft had 1100TT.
dublinpilot wrote:
Probably the best option is to make a mayday call, and get down to 50 feet above the surface and continue. That means if you decide to ditch, you can execute it very quickly, which means you can run longer with the fire problem.
I guess that’s what I would do in the circumstances.
I only had burning smell / smoke once, and that was a radio dying. It decided to do so right above LAX….. probably one of the better places for an emergency to happen, still disconcerting though. It started with the r/t audio quality deteriorating, then came the smell. At first I thought it came from the outside, as I was just over a huge refinery, then a faint smoke appeared. Switched that radio off and informed Santa Monica (my destination a few miles away), that I might have to go NORDO. In the event, switching this one piece of equipment did the trick and the – short – rest of the flight was uneventful.
