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How would you react?

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How would you react?

Old 27th Apr 2001, 05:59
  #1 (permalink)  
Capt Claret
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Question How would you react?

Flying over the GAFA yesterday, the F/O and I were discussing how we thought we would react to an uncontained fire in the underfloor cargo hold.

The aircraft, a transport category jet, has no fire/smoke detection, nor fire fighting capability, in the baggage hold.

Our conversation raised a number of questions, given that we were often >100 nm from a suitable aerodrome.
  • How would we, the tech crew, know there was a fire?
  • Assuming progressive cabin crew reports of smells, perhaps smoke, perhaps heat, how long would it take to come to the conclusion that there was a fire?
  • How would we come to the conclusion that a forced landing was required, rather than a diversion for some 100+ nm?
  • Would we make a forced landing in the bush?
  • Would we commence an emergency descent to a low altitude to hopefully give the chance of a successful forced landing if it became an obvious necessity?

For the record, not many decisions were made. We thought perhaps a major highway, parallel but offset from our track whilst enticing, may have been more dangerous given the road trains and car/caravan traffic. We also touched wood.

I'd be interested in your thoughts and suggestions.

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bottums up !

[This message has been edited by Capt Claret (edited 27 April 2001).]
 
Old 27th Apr 2001, 07:18
  #2 (permalink)  
compressor stall
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Red face

Clarrie,

I too have thought about similar, albeit in light pistons. Flying in circles for 6 hours a day in the Gulf out of sight of land has lead me think what would I do if I had a fire? Ditch immediately, or for how far would I attempt to try to fly, and how would I know when to stop, presuming I still hada choice to make? Real lap of the gods stuff all in all.

FWIW, how many major highways are there in the GAFA? Like to see you put it down on the Gunbarrell highway!

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Those who restrain desire do so because theirs is weak enough to be restrained.
William Blake
 
Old 27th Apr 2001, 10:01
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Elevation
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How about staying at your flight level and depressurise the hull ?
At 30,000+ feet, don't think there will be enough O2 to sustain a fire.
Then again, it may be my brain going loony again !
Ta !
 
Old 27th Apr 2001, 12:20
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Capt Claret
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Good thought there Elevation, that one didn't make it into our list.

Does anyone know what pressure height, if any, that a fire cannot continue?

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bottums up !
 
Old 27th Apr 2001, 16:50
  #5 (permalink)  
The The
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As a side, CASA following an FAA directive has an AD for all class D cargo compartments (designed to contain a fire only) to be upgraded to Class C (smoke/fire detection and extinguishing) for passenger aircraft. This must be done by 7/10/04.

 
Old 27th Apr 2001, 22:33
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Iz
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Tcas climb, the B767 has fire detection and protection in the cargo holds. But okay, say that the extinguishing system does not kill the fire, you're still in the same situation.

When you're dumping the pressure at crz alt, you'll have to drop the oxy masks and the real danger when using the oxy system is that if the fire catches that, you won't survive.

When the fire is also fed by flammable chemicals in the cargo hold, dumping the pressure would only make it harder for yourself.

During some flight safety fire training I followed a few weeks ago, we saw videos of cabin fires. On average, you'll have about 2-3 minutes from the time that the fire reaches the cabin till flashover occurs - at that time, everyone in the cabin will be dead.

Is it still allowed by law to have ETOPS flights in aircraft that don't have cargo fire protection?
 
Old 27th Apr 2001, 23:24
  #7 (permalink)  
pied piper
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How is a decompression going to put out a fire?

there is enougth Oxygen to feed the engines presumably, so why not a fire?

scuse the bad spelling
 
Old 28th Apr 2001, 01:47
  #8 (permalink)  
little red train
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Piper,

The engines compress the Air, increasing the 02 avilable. for example if the APU is required, a decent is sometimes required to get into the "Thicker" Air.

Altought they do use gas stoves on top of everest dont they?
 
Old 28th Apr 2001, 04:27
  #9 (permalink)  
thermostat
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The composition of the atmosphere does not change significantly up to 300,000 ft. (56 sm).It consists of approximately 78% nitrogen, 21% oxygen and 1% other gasses. What does change is the pressure of 760mm Hg at sea level, half that at 18000 ft, one quarter at 34000 ft and 1/10 th that at 53000 ft.
There is just as much oxygen at 39000 ft as at sea level, just less pressure.
Hope that helps. Thanks.
 
Old 28th Apr 2001, 07:55
  #10 (permalink)  
OzExpat
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Talking

Bend well down from the hips and kiss my @rse goodbye. Then wait for the sound of my @rse frying!

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Dispela olgeta samting i pekpek bilong bulmakau!
 
Old 28th Apr 2001, 13:23
  #11 (permalink)  
Capt Claret
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Wink

Ozexpat,

Like your style, and you're probably right. Hopefully the obligatory home video will survive and make it to Funniest Home Videos!

Thermostat,

When you say there's as much O2 at FL390, are you talking volume? I'd assume that there's much less mass. Would the reduced mass have any bearing on the sustainability of a fire?

Tcas,

I guess it goes without saying that one of the considerations re depressurising would be the necessity to deploy pax and crew O2.


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bottums up !
 
Old 28th Apr 2001, 17:24
  #12 (permalink)  
Tinstaafl
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Unhappy

The chemical reaction that occurs during burning is based on the ratio of the mass of air to fuel.

The density is much, much less at altitude than at lower levels so the mass of O2 available for the given amount of fuel is different.

When a flame is 'blown out' it is extinguished because the mixture required to support combustion is leaned to the point that combustion is no longer possible.

(I wonder if there is also an element of moving the point of combustion away from the fuel source faster than the flame front can propagate?)

Reducing the available O2 has the reverse effect, making the mixture richer. This can reach a point where combustion can't occur. How many have experienced a rich cut in a piston a/c? Or seen the demo of dropping a lit match into an oil drum filled with petrol (I was happy to see the film of it and never felt the need to try it at home)?

I think the point about depressurising is a good one. Even if it doesn't completely extuingish the fire it will certainly reduce its intensity & rate of spread.

[This message has been edited by Tinstaafl (edited 28 April 2001).]
 
Old 28th Apr 2001, 20:23
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Prof2MDA
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FWIW, the procedure for dealing with fires in cargo aircraft (in areas that do not have extinguishing)is to depressurize the aircraft and fly at FL250. They pick FL250 as a balance due to oxygen concerns, time to get on the ground, etc. According to people that are knowledgeable on the subject, it works. I asked ALPA's dangerous goods specialist this question recently, actually, and he confirmed that the procedure was sound as long as the material causing the fire did not generate its own oxygen (obviously).
 
Old 28th Apr 2001, 23:50
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Spearing Britney
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Exclamation

But when depressurized you would be forced to reduce rate of descent to well below that which could be maintained when operating normally - potentially increasing time in the air...
 
Old 29th Apr 2001, 09:25
  #15 (permalink)  
 
Join Date: Aug 1998
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Exclamation

I would strongly advise against depressurising and staying at altitude.

At 34,000 ambient pressure is only 188mmHg, so 100% oxygen would supply a pulmonary partial pressure of 101 mmHg, after allowance is made for 87 mmHg of water vapor and CO² in the lungs. As passenger & Cabin crew oxygen systems are not designed for pressure breathing both would suffer increasingly severe hypoxia above this altitude, those that failed to wear their oxygen mask would quickly lose consiousness.

Aircraft with chemical Oxygen generators (not the 146, I know) have only about 12 minutes of Oxygen available (and you still have to descend remember!) and the generators themselves put out a lot of heat.

More importantly perhaps, keep the aircraft cabin at such low pressures and Nitrogen will come out of solution in the blood and fatty tissues and form bubbles, know as Dysbarism or Decompression Sickness, in the passengers and crew (including the pilots!). Get the bends and you may not be able to recover the aircraft later.
Checkboard is offline  
Old 30th Apr 2001, 15:25
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Slasher
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Cool

Yeh spot-on Prof2. But another specialist reckons to maintain present altitude if above FL 250 but below 410.

Checkboard dont forget your trying to get the cargo fire out first. The average tech crew bottle lasts about 15 minutes (undiluted), and the pax might flake but they wont die. What will kill them (and you) is a cargo fire if nothings done.
 
Old 30th Apr 2001, 22:47
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Spooler
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Capt Claret, when the oxygen level reduces to a level of about 13-15% from the normal value of 21% a fire will extinguish, as the oxygen/vapour mix is incombustable. I can't believe that it is not mandatory for cargo holds to have a halon or halon substitute (FM-200) as a very rapid fire extinguisher method. Get rid of the O2, get rid of the heat and things are a little less drastic than they were a couple of seconds earlier.
 
Old 30th Apr 2001, 23:33
  #18 (permalink)  
John Boeman
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Yes, I was asked that question by a very knowledgeable and respected trainer (thanks Dave M.) as we crossed the pond while I was being checked out on ETOPS some years ago.
His advice, in the event of an UNCONTROLABLE fire and unable to reach an alternate, was to descend to FL250 and depressurise, as stated by Prof2 and Slasher.
In the circumstances described, I do not think that Checkboards concerns are a consideration.
It’s a choice between definitely dying or maybe surviving.
 
Old 1st May 2001, 13:39
  #19 (permalink)  
dv8
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The ATR 42/72 smoke(fire) in in cargo config. had us landing ASAP or if not possible ........."climb and maintain min. FL160,FL200 recommended"
I have never felt happy about that and touch wood never had too never being that far from divertion A/D's
 
Old 1st May 2001, 14:57
  #20 (permalink)  
ft
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<font face="Verdana, Arial, Helvetica" size="2">
(I wonder if there is also an element of moving the point of combustion away from the fuel source faster than the flame front can propagate?)
</font>
Yup, that's why you have flameholders in the engines. Recall mach cones. The same thing happens when you have an ignition point in an airflow, a cone shaped flamefront.

Cheers,
/ft
 

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