"...if after 30 seconds....discharge...."
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It is a good point, LEM, and I've inadvertently drifted away into the evac cklist. I'll ask a few of our trainers what they think. To my mind, delaying the second bottle is pointless ON THE GROUND. You could be about to evacuate. Who wants to wait those extra 30 seconds to see if it works?
Last edited by BOAC; 17th May 2003 at 17:54.
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Hmm Lem, good points made there. I think a little bit different now 
Anyway on the ground i still sincerely think that waiting for 30 secs with passengers disembarking (decision has already been made anyway) it's pointless to wait and see if after 30 sec. the fire has extenguished.
I mean if you were not able to turn the aircraft away from a prevailing crosswind, the fire leaps quikly over the wing to the cabin and to the other side of the plane.
If the fire hasn't extinguished after 30 sec when bottle 1 is fired, you're about certain that the second bottle doesn't help either. Because probably the fire is already going further than the core of the engine. I do think that a little delay is there for a reason. So wait let's say 10 sec. or something, then discharge nr2 and get the hell outta there....
And again, in the air it's completely different reasoning, and 30 sec logic is well in place there.
Good subject for debate though on the ground.
Anyway on the ground i still sincerely think that waiting for 30 secs with passengers disembarking (decision has already been made anyway) it's pointless to wait and see if after 30 sec. the fire has extenguished.I mean if you were not able to turn the aircraft away from a prevailing crosswind, the fire leaps quikly over the wing to the cabin and to the other side of the plane.
If the fire hasn't extinguished after 30 sec when bottle 1 is fired, you're about certain that the second bottle doesn't help either. Because probably the fire is already going further than the core of the engine. I do think that a little delay is there for a reason. So wait let's say 10 sec. or something, then discharge nr2 and get the hell outta there....
And again, in the air it's completely different reasoning, and 30 sec logic is well in place there.
Good subject for debate though on the ground.
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Read the Boeing QRH 737 for Passenger Evacuation, it's covered there. If you have any further doubts about waiting for 30 seconds on the ground before firing the second bottle I suggest you contact Boeing or take it up with your Flight Safety Officer.
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Pancho - I think you have, like me, been 'seduced' down the evac line, and I THINK LEM is referring to the execution of the engine fire drill BEFORE the evacuation, while the situation is being 'assessed' after the STOP, no?
I have a view that the amount of extinguishing agent provided by the manufacturer per "shot" will be based on the volume of space inside the engine cowlings. This volume can only take so much extinguishing agent. If you discharge both together, a significant amount will be forced outside the engine compartment and lost. If you fire one shot and then wait a period of time (and 30 seconds seems the standard), you will have the full quantity of the second shot left if the fire is not fully extinguished by the first shot, minimising the amount of agent lost outside the cowling.
Having said that, if the manufacturer's Flight Manual instructs you to fire both together, you should do so unless you have good reason not to.
Having said that, if the manufacturer's Flight Manual instructs you to fire both together, you should do so unless you have good reason not to.
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One thing to consider if you fire both firex cylinders at the same time on the ground:
You only have two shots to put the fire out. If you fire the first cylinder and some time later the fire reignites, you have a second shot to put the fire out. What would you do if you have already fired both cylinders? If you have ever put a fire out with a fire extinguisher you will be aware that secondary flare up can occur if fuel and a source of ignition remain. I would be hanging out for the 30 seconds to see whether the first shot had worked before using up my last chance.
You only have two shots to put the fire out. If you fire the first cylinder and some time later the fire reignites, you have a second shot to put the fire out. What would you do if you have already fired both cylinders? If you have ever put a fire out with a fire extinguisher you will be aware that secondary flare up can occur if fuel and a source of ignition remain. I would be hanging out for the 30 seconds to see whether the first shot had worked before using up my last chance.
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Interesting points made there.
All these prove that there's little to reinvent , today, in aviation.
In this example, with a fire on the ground, just follow the manufacturer's procedure: on an Airbus, discharge both bottles right away; on a 737 discharge the second one after 30 seconds.
All these prove that there's little to reinvent , today, in aviation.
In this example, with a fire on the ground, just follow the manufacturer's procedure: on an Airbus, discharge both bottles right away; on a 737 discharge the second one after 30 seconds.
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Stick to the checklist - ie if the required drill (as Boeing) says 'wait 30 seconds', do so. Two reasons:
1) Liability issues are protected if it all goes wrong because you 'only followed orders' (as they say)
2) as 'roundwego' says, there is some doubt about the effectiveness of an immediate second shot (ask his partner!!
)
In any case, you always have the option of starting an evacuation during those 30 seconds if you feel uneasy about the wait.
hereford
duty lert
1) Liability issues are protected if it all goes wrong because you 'only followed orders' (as they say)
2) as 'roundwego' says, there is some doubt about the effectiveness of an immediate second shot (ask his partner!!
)In any case, you always have the option of starting an evacuation during those 30 seconds if you feel uneasy about the wait.
hereford
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Points taken guys, always good to broaden the horizon. Though I do think that some instructors have different believes about this issue. Probably because of the very same reasons we have discussed...
The big red line is easy to follow, probably is the best anyway.
The big red line is easy to follow, probably is the best anyway.
