What goes on when when a big plane dumps it's fuel ?

[Kobal2]

@48Willys

It is also hard on airplanes to run out of fuel in flight.

… one would think, yeah !

[Leo_Bloom]

Among the libraries of reporting and monitoring information, is alerting any environmental agencies or specific record-keeping of fuel dumps (where, what, etc.) required?

Dark rain and all.

[LSLGuy]

Our company procedures require that we report a fuel dump to HQ after landing. As a separate matter we’ll advise ATC when starting and stopping fuel dumping.

I have no clue whether any of that info goes any farther.

I do know that spilling even a couple gallons of fuel on the concrete terminal ramp is EPA-reportable. That gets a remarkable amount of supervisor attention for what seems like a pretty tiny incident. So my educated guess would be that fuel dumping is reported to EPA in the US or the local country equivalent.

[AK84]

@LSLGuy

Our company procedures require that we report a fuel dump to HQ after landing. As a separate matter we’ll advise ATC when starting and stopping fuel dumping.

I have no clue whether any of that info goes any farther.

I do know that spilling even a couple gallons of fuel on the concrete terminal ramp is EPA-reportable. That gets a remarkable amount of supervisor attention for what seems like a pretty tiny incident. So my educated guess would be that fuel dumping is reported to EPA in the US or the local country equivalent.

Out of curiosity what were the rules for fuel dumps in the military? (I am guessing at the minimum half a dozen forms to fill out :)).

[LSLGuy]

I have no idea; I never flew heavies in USAF.

We carried droppable fuel tanks in the F-16, but unlike in WWII they weren’t considered disposable. The expectation was you’d bring them back from every mission in peace or war.

There was a “dropped object” report that got filled out if anything fell off or was jettisoned out of the ordinary. The one time you’d be expected to jettison external fuel tanks is following an engine failure. This was true in both single and two-engine jets. That’d rate a dropped object report. Although in the case of the single engine jet you’d need 3: One for the tanks, one for the jet, and a third for yourself and the seat.

[AK84]

@LSLGuy

I have no idea; I never flew heavies in USAF.

We carried droppable fuel tanks in the F-16, but unlike in WWII they weren’t considered disposable. The expectation was you’d bring them back from every mission in peace or war.

There was a “dropped object” report that got filled out if anything fell off or was jettisoned out of the ordinary. The one time you’d be expected to jettison external fuel tanks is following an engine failure. This was true in both single and two-engine jets. That’d rate a dropped object report. Although in the case of the single engine jet you’d need 3: One for the tanks, one for the jet, and a third for yourself and the seat.

Or when you get a “Russian bombers sighted” report. (Or is jettisoning fuel tanks toget to bombers faster, also a WW2 relic).

[LSLGuy]

@48Willys

…
I would have to look it up, in the FARs, but IIRC: If a commercial aircraft has the ability to take off with a full fuel load weight that exceeds its maximum landing weight by 10 percent, it is required to have a fuel dumping system. IE: If full fuel, cargo, & passengers can be 110 percent or above the maximum landing weight, a fuel dumping system is required. Again, IIRC, The above mentioned aircraft do not have that issue. …

You got me curious so I looked it up. As of today it’s 14 CFR 25.1001 which can be found at eCFR :: 14 CFR 25.1001 -- Fuel jettisoning system. (FAR 25.1001). The reg has been amended from time to time, most recently in 2002.

The official answer (now) is that fuel dumping capability is required if the aircraft can’t make the required go-around performance after taking off at maximum takeoff weight then making a quick (15 minutes) return to a landing.

If the airplane can fly the go-around at that near-maximum weight there’s no need for a dump system. If the airplane can’t fly the go-around at that weight, the dump system must be installed and sized to reduce the weight enough to meet the go-around requirement within the 15 minutes.

The go-around performance requirements are complicated and not relevant here except to say they include considerations for two cases: all engines operating and one engine failed.
My semi-informed speculation is that by and large the other takeoff / go-around performance requirements for a two-engine aircraft pretty well demand it meet this performance standard without needing the ability to dump. There may be a few corner cases where that’s almost but not quite true.

The differing performance requirements on 3- and 4-engine aircraft OTOH have the effect that fuel dumping capability is almost always required.

Most industry pundits believe the last 3+ engine airliner has already been introduced. No new ones are being designed anywhere and the only ones still in production are the 747 and A380. Both of which are not dead yet but are looking sickly.

So fuel dumping, like so many other artifacts of the early days, is probably going the way of the dodo.

[Leo_Bloom]

@engineer_comp_geek

This isn’t really my area of expertise, but I know it’s possible to catch dumped fuel on fire because you can do it intentionally in a fighter jet with an afterburner. It’s called a “zippo”, named of course after the cigarette lighter.

Here’s a video of an F111 doing it:

There’s no real danger to the plane since the fuel won’t burn unless it is mixed with air (oxygen), and the fuel coming out of the plane is all fuel and no air. So it won’t start burning until it has had a chance to spread out through the air a bit. From what I recall, the rate of flame moving through fuel is also slower than the airspeed of a typical plane. The fighter in the video is constantly lighting the fuel with the afterburner. Without that constant ignition, the flame can’t catch up to the plane. The plane just moves too fast for it.

Without an afterburner, you are going to have a hard time getting the fuel to light. It needs some sort of source of ignition. But again, even if you do manage to get it to light through some sort of static discharge or something, all you are going to do is make a fancy flame show. It might scare the bejeezes out of the passengers (FIRE!!!) but other than that, no biggie, as far as I’m aware.

Just to be clear: afterburners are not designed for fancy flame shows, and that Zippo display is used/useful only for that, with obviously wasteful (except for Zippos) fuel efficiency/thrust payoffs…

…or is it, as it happens and also why pointed out in this thread, something that happens during a normal fuel dump (i.e., it’s gotta get dumped somewhere, and it winds up being thus “afterburner,” the circumstances for which in modern fighters is severely limited, as LSL notes?

[Kobal2]

It’s deliberate. The fuel dump valve is a little below the actual engines and sprays downwards, which is why the pilot of the F-111 has to initiate a slow climb/high angle-of-attack drift forward to get the flames going. It doesn’t happen during a normal dump.

[JHBoom]

@AK84

Out of curiosity what were the rules for fuel dumps in the military? (I am guessing at the minimum half a dozen forms to fill out :)).

In Air Mobility Command (the part of the USAF that owns the majority of the “heavy” aircraft in the USAF), there’s several forms to fill out if you dump fuel, or “adjust gross weight”. As long as there’s a good reason for the dump, a crew won’t be in any trouble.

[Leo_Bloom]

@Kobal2

It’s deliberate. The fuel dump valve is a little below the actual engines and sprays downwards, which is why the pilot of the F-111 has to initiate a slow climb/high angle-of-attack drift forward to get the flames going. It doesn’t happen during a normal dump. ital add

Got it.