Jettison Fuel

Q: I know that planes sometimes jettison fuel? Is this to prevent an explosion during a crash?

With larger planes, the maximum allowable weight for takeoff is greater than the one for landing. This makes sense, if you think about it, as touching down puts higher stresses on the airframe than taking off. During flight fuel is burned away -- to the tune of hundreds of thousands pounds on longer routes -- reducing weight to within landing limits. (All of this is planned out before departure, as max weights for a given flight are contingent on many things, not simply the book restriction of the plane itself.)

Now, let's say something happens soon after takeoff and a plane must return to the airport. In many cases it's too heavy. Rather than tossing passengers or cargo overboard, it will jettison fuel through plumbing in its wings. I once had to dispose of more than 100,000 pounds this way over northern Maine, a procedure that took many minutes and afforded me a lavish overnight at the Bangor airport Hilton.

Unless there's a serious emergency, "dumping" takes place at high enough altitudes where the kerosene dissipates long before reaching the ground, and no the engine exhaust will not ignite the stream.

In certain situations a crew may elect to land even when exceeding max landing weight. There is the risk of damage to the plane, of course, but the risk of delay could be greater.

Article added on September 20, 2005

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