Airline Emergency Procedure Question

[HeyHomie]

Hypothetically…

A 747 is flying over Springfield, Illinois. The pilot is going to make an emergency landing at Bushwacker Regional Airport. As a safety precaution, he jettisons his fuel.

What happens to this fuel? Does it instantly evaporate and become a more-or-less permanent part of the atmosphere? Or does it rain down on my house?

[Johnny_L.A]

It would depend on how high the aircraft is, of course; also on the weather conditions. But the fuel should evaporate well before it hits the ground.

[bernse]

Agreed. It should. As a percaution though it is done if possible over an unpopulated location. When its not possible to be over the ocean and the plane is >FL10 I would sure not want to be the guy roasting weenies over an open fire below him though! Just in case, or course!

[Creaky]

Aviation fuel does evaporate very quickly. The 100LL fuel my Piper Warrior uses evaporates within seconds when I flick it in the air after sumping the engine. Jet fuel is mostly kerosene as I understand, so I would expect the same. That’s my WAG - any jet drivers who have first hand experience feel free to refute me.

[TheLoadedDog]

I used to live under the flightpath in Sydney. The planes would have been at about 700ft I think (a bit hard to tell from immediately below them). People in my suburb used to complain about weird oily stains appearing on their washing when they hung it out to dry.

They were the lucky ones though. One guy got a piece of Thai Airways engine cowling in his bedroom.

[Zweistein]

I was once in the experience being in a emergency in a 747 when going from Heathrow to Mexico. Due to hydraulic problems with the plane we had to return to London (we just left the coast of Scotland) the pilot headed for Ireland and while traversing the Irish sea he dumped fuel before reaching land again. I assume this was done to avoid any problems above land.

[brachyrhynchos]

According to this EPA page:

EPA commented on emergency fuel dumping. As noted on pages 4.3-8 and B-1-18 in the FEIS, emergency fuel dumping is extremely rare. DON policy directs that it not occur below 6,000 feet above ground level unless necessary to save the pilot and/or aircraft. In the event of an engine failure on a dual engine fighter, like the F/A-18, the pilot should be able to operate with the remaining engine or climb above 6,000 feet before dumping fuel, thus minimizing the impacts associated with the release of the fuel. (Above 6,000, the fuel has enough time to completely vaporize and dissipate before reaching the ground, and thus has a negligible effect at ground level.) Therefore, any impact from fuel dumping would not be significant.

(bolding mine)

And according to this Canadian EIS:

A dispersion model was used to predict the quantity of fuel reaching the ground for the 16 fuel dumping incidents documented by CFB Goose Bay in 1992. The model took into account the operational circumstances (quantity of fuel dumped, release altitude, duration of release) and the prevailing meteorological conditions associated at the time of each release.

The maximum fuel deposition flux (1.16 mg/m2) resulting from a fuel dumping is not likely to cause any significant contamination on watersheds or soils.

I think, for the most part, you and your weenies are safe, bernse. But I guess the question might be how often below 6000 ft does dumping occur?