question about dumping fuel

[mattpilot]

I always wondered about dumping fuel. Someone told me its only legal to dump fuel over sea. Then one of my instructors, old ex-eastern captain, told me that they once dumped fuel over land because of an emergency.

Now the question, what happens when fuel is dumped over land. I assume the fuel would fall to the ground like rain? I also assume that the fuel is still combustable? So, what happens when someone on the ground is standing there having a smoke - and suddenly this fuel-rain falls on him - will he explode? :D

Or would the fuel evaporate? But lets say it does hit the ground and someone is standing down there with something to ignite the fuel - what would happen? :D :cool:

[Notso Fantastic]

Fuel dumping should take place above a minimum height which in my company is 6000'. I have never heard reports of such fuel being detected on the ground. At a maximum rate of 2 tons a minute and a likely speed of 4 miles a minute (240 mph), it's a pretty low concentration that will be well dissipated by a vortex. I'm sure nobody will spontaneously combust whilst having a quiet cigarette admiring the stars!

[tinyrice]

If the choice is losing the aircraft or the fuel, you lose the fuel. While its preferable to go and find a large body of water to dump over to reduce the number of people you're dumping on, plus it helps to dissipate the stuff, there have been a number of incidents over the years that have required dumping just after departure for the aircraft's safety. Have you seen the Peoples Express 747 video out of LGW? They started dumping over Russ Hill and finished out over the Channel. For the most part the gas either evaporates, or comes down as an oily mist which upsets the motorists amongst us. In either case, I think it would be almost impossible to get the fuel air ratios to the point of being combustible

[Albatros6]

During normal Ops, a Airliner would leave a fuel trace, if the fuel would'nt get burned in the Engines, of a diameter of a quarter of an inch. Fuel dumping gets a trace of about three times that diameter, or equalling about 0.3 liter per meter travelled. The fuel to air ratio for a burnable mixture is about 1:15, which means if the fuel is mixed with more than 4.5 cubic-meter of air, it's not combustiable anymore. So, if fuel get's dumped, the only area for ignition is very close to the aircraft, but as the spray-pattern grows to more than 2.5 meters in diameter, it's too lean for combustion. The resulting diameter of the droplets will keep it floating with hardly any sinkrate soon, and sunrays will sublimate the fuel finally.

Hope you never have to use it.

[Bigears]

I've seen a jag dump fuel over farmland. He was at about 1000ft.
I was approx. 1-2 miles away, and saw a very obvious haze behind him.
Pilot-twr conversation confirmed that he was dumping after a birdstrike.

[professor yaffle]

in the uk:
over water if poss
should be above 10,000feet if poss
if not then in winter above 7,000ft and summer 4,000ft if poss
if not then dump the fuel as high as is poss
then land!

prof

disclaimer - from memory and not had the benefit of confirming it with the docs but you could find this information in the mats part 1 which i don't have a link for i'm afraid

[5milesbaby]

yaffle, thats exactly it as far as I'm aware. Using the 4000/7000ft guide means ground unaffected, any lower and concerns increase slightly!!!!!!!

Don't think anyone told the BWIA Tristar many years ago though that struck tail on departing FRA and landed LHR, dumping fuel all down the final approach track over London, until stopped on Tarmac!!!!!!!!!!!!

[Fokker-Jock]

When fuel is dumped, the fuel spraying out from it's dump nozzles is blended with the air at a speed of x-kts and the ram air pressure hitting the fuel is so high that the fuel heats up and most of it evaporates instantly.
The fuel that doesn't evaporate, will on it's way down.

The CAA have guidelines as to where and when to dump fuel. But in an emergency you dump it wherever and whenever you feel like in order to meet the situation you're in.

Companies usually have strickter procedures on this subject.