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Imagine a hypothetical scenario where a jet heavily loaded with fuel experiences more than one engine failures after $V_{1}$. Then I suppose that losing some weight would be beneficial since the airplane is not designed to sustain climb with such limited thrust. In such a case a) how much would dumping fuel help in this emergency (i.e. is the rate of dumping fast enough?) and b) could the captain proceed to do it without ATC authorization if he/she considers it necessary?

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    $\begingroup$ According to aviation.stackexchange.com/questions/8136/… a 747 can dump 6000 pounds of fuel per minute. Given that (from what I found) it typically carries at least 200,000 pounds, and has an MTOW of over 800,000 pounds, it seems unlikely you'd dump enough fuel fast enough to make any difference. Moreover, in the situation you describe, I guess there'd be a fair chance that the plane will be back on the ground pretty quickly, and it might not want to land in a huge puddle of fuel. $\endgroup$ – Nate Eldredge Feb 6 '16 at 7:30
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    $\begingroup$ You do not do it en.wikipedia.org/wiki/US_Airways_Flight_1549 $\endgroup$ – Trebia Project. Feb 6 '16 at 10:08
  • $\begingroup$ If you are a twin jets you have bigger problem. $\endgroup$ – vasin1987 Feb 7 '16 at 10:14
  • $\begingroup$ Clearly if it is an all engines out situation there will be no difference. I am refering to somehting like a 747 or MD-11 losing 2 engines. $\endgroup$ – user13363 Feb 19 '16 at 7:18
  • $\begingroup$ You may instead elect to land overweight. A dual-engine failure is very rare and I would probably risk an overweight landing than waiting to discover the underlying cause in the air. $\endgroup$ – Hugh Jul 20 '16 at 5:53
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You would not attempt this. Aircraft are certified to climb with engines inoperative after V1, they would just climb to a holding altitude and run the checklist. They would rather not attempt to any cruise altitude. Running the checklist you would determine if you are above the maximum landing weight (MLW) and decide to burn or if able, to dump fuel.

Dumping fuel during the takeoff/rotation phase is not advisable to be honest, as you would leave a contaminated runway behind. Sure, most of the fuel will evaporate, but there will be a contamination nonetheless.

I will quote Nate Eldredge's comment shamelessly for another item to consider:

According to How is fuel dumped in aircraft? a 747 can dump 6000 pounds of fuel per minute. Given that (from what I found) it typically carries at least 200,000 pounds, and has an MTOW of over 800,000 pounds, it seems unlikely you'd dump enough fuel fast enough to make any difference.

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    $\begingroup$ Aircraft are not certified to climb with engines (plural) inoperative after V1, single engine yes, multiple no. In that case as a pilot my concern would not be contaminating the runway, it would be getting the aircraft high enough to get to a landing spot. I'm not going to sacrifice my life or my passengers over a concern of runway conditions. Really the meat of this boils down to "how much, how fast", and I would agree that it wouldn't happen fast enough to make a difference. $\endgroup$ – Ron Beyer Feb 7 '16 at 3:47
  • $\begingroup$ @RonBeyer If you plan to return to your field, a contaminated runway is actually something you will have in mind if its the only one available... $\endgroup$ – SentryRaven Feb 7 '16 at 14:39
  • $\begingroup$ As the alternative to an off field landing, it would still be low on my list of priorities. I can't imagine given a contaminated runway versus an off field, that the pilot would take off field. Using all the runway and crashing in the overrun is still preferable. $\endgroup$ – Ron Beyer Feb 8 '16 at 4:13

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