Are large aircraft ever defueled (i.e. removing fuel from their onboard tanks), and how common is it if so?
What happens with the fuel afterwards? I don’t imagine it can just be reused without some sort of testing or inspection, especially if they’re completely emptying the tanks (assuming contaminants will build up over time in the unused portions of fuel).
There was an episode of Dirty Jobs in which Mike Rowe helped with the servicing/inspection of a KC-135’s in-wing fuel bladders. This involved physically climbing inside the drained fuel bladder. Which is to say yes, at least KC-135s are defueled now and then.
If you’re draining fuel from a plane that was just pulled from service, then it should be fine for use, although I expect it’s common procedure to pass it through a filter before putting it back into any aircraft.
If you want to get rid of fuel you’ve deemed unusable, there are any number of places that will pay you for it. example here.
I imagine any such removed fuel is inspected, filtered if need be, and reused. Even without draining, fuel for aircraft of any size is routinely sampled and inspected prior to take off.
I don’t have experience with large planes, but with the smaller ones sometimes the drained fuel was re-used in ground vehicles, as it’s basically either fancy gasoline (avgas) or kerosene (jet fuel). Probably not entirely kosher, but we’re all aware of that gap between theory and practice, right?
Even so - the amount of fuel a passenger or cargo jet holds is immense. And there are probably a lot of rules and regs surrounding handling it. If it could be re-used I see no reason it wouldn’t be, even with an inspection process required. Aviation fuel is considerably more expensive than the equivalent ground vehicle fuel, it probably is economically worthwhile to recycle it whenever possible.
Yes, it can be. I was on a plane that had to have some fuel removed because they put too much in. I believe the reasons for removing it are to reduce weight which increases mileage and to reduce weight which, IIRC, means they pay a smaller fee for using the runway at their destination.
As far as I know they just pumped it right back into the underground network/tanks that they used to fill the plane with.
I don’t think it’s entirely uncommon to take some fuel off if they realize they’ve added too much.
For commercial airliners, the most likely reason to need to defuel a plane is because of a last minute aircraft swap. For example aircraft A was scheduled for flight 123, but has a mechanical problem. So the airline swaps it with aircraft B, which had been scheduled to fly flight 456, which is a longer light. Aircraft B has already been fueled for the longer flight, but now with the passengers from flight 123, plus their bags, plus the fuel, it’s above the maximum takeoff weight. So the need to get rid of some fuel. In my experience as a passenger what they did when than happened on a flight I was on was to taxi over to a remote part of the airport, set the brakes, and throttle up the engines for a few minutes until they had burned off enough fuel. That’s obviously wasteful, but I imagine it was more expedient than bringing equipment over and pumping fuel out of the tanks.
Any air carrier aircraft can be defueled the same way it is fueled. The fueling hose is attached to the fueling manifold and the fuel departs the aircraft. Most aircraft fuel servicing vehicles can defuel as well as fuel - it’s just an additional valve that gets opened. The pump on the fuel truck pumps out of the fueling hose, through the filter on the truck, and back into the truck’s tank (backwards from how it usually works).
The fuel is essentially the same fuel as it was before it went into the aircraft. The tank inside an aircraft is of the same quality as the tank for the fuel truck, and the same quality as the fuel storage tank at the airport. Jet fuel is filtered every time it gets moved (delivery into storage, storage into the truck, truck into the aircraft). Contamination isn’t really a problem.
The rules for reuse of aircraft fuel (and everything else conceivable having to do with aircraft fuel quality) are in a document called ATA103, Standard for Jet Fuel Quality Control at Airports. It’s also $445, if you’re looking for some light reading.
Thank you, all. I was imagining a plane that needed to defuel after landing (maybe this is it’s last flight, or something), but it sounds like that wouldn’t be any different.
I was thinking contamination would be an issue because I remember that episode Machine Elf mentioned (or maybe another show) where people are walking around inside the planes fuel tanks, with no special precautions taken (at least that I saw) to prevent bringing in stuff on their shoes. Also, don’t the tanks rust or corrode over time? So the tank itself could be contaminating the fuel.