747 Fuel Dump

[epmi314]

I live about 25 minutes from Metro Airport in Detroit Michigan. I notice a large plane flying by with what I initially thought were contrails but it was far too low. This was a 747 heavy bound for Tokyo with a #2 engine problem that had to return to the airport. They spent about 30 minutes circling and dumping fuel until they were light enough to land. They had 396 souls aboard so it is great to hear they landed safely.

No C&C on the shot is necessary, I just thought it was kind of nuts!

[Colin Southern]

As an (ex) pilot of (considerably) lighter machinery, I must admit to still being confused as to how they can stand the structural weight of the fuel at take off, but not the same for a landing. I can appreciate that if the landing is going to be a rough one then that could certainly stress the undercarriage a bit -- but if it's a "nice day" with the potential for a smooth landing (a-la "autopilot!) then I've always wondered why they couldn't just ease it back on to the deck without having to dump many tonnes of fuel

[epmi314]

Colin,

After some additional research I am amazed at how much fuel these planes can hold and, with a little math, how much it weighs. It still amazes me these things ever get off the ground! Nonetheless, it sounds like it is significantly easier to get in the air than back to earth when laden with fuel.

[FrankMi]

Heavy aircraft, like a Boeing 747 are designed to be landed as much as 200,000 pounds lighter than they can safely take off. The additional stresses placed on the aircraft during landing make landing heavy very dangerous.

In cases where an aircraft so designed was forced to land heavy, not only is there increased risk of damage and loss of control, but the risk of fire is significantly increased. For example, consider Southern Airways Flight 242 on April 4, 1977. The DC-9 lost both of its engines due to hail and heavy rain in a thunderstorm and, unable to glide to an airport, made a forced landing on a highway near New Hope, Georgia, United States. The plane made a hard landing and was still carrying a large amount of fuel, so it burst into flames, killing the majority of the passengers and several people on the ground.

Most military aircraft that take off heavy have the same issue and add to that is the risk of live munitions going off as well. This is routinely done for aircraft carrier landings.

Hope this helps clarify the reasons for fuel jettison under these circumstances.

[Colin Southern]

Hi Frank,

Thanks for that - yes, they certainly are the well-documented official reasons. To the best of my knowledge though, their SOPs don't make any distinction between having to make a priority landing with turbulant crosswinds on a "short" runway (which would be greatly ingrease the chances of over-stressing the airframe, undercarriage, and brakes, -v- the potential to "grease it on" in calm conditions on a long runway.

So I guess what I'm really questioning is "SOPs aside, realistically, is it really a problem if the landing is to be carried out in ideal conditions"? (ie a barely perceptable 0.25g landing, rather than a bone-shaking / pop the overhead lockers open 2.0g worst-case-scenario that the SOP is (probably) written for).

[FrankMi]

There is certainly some safety margin in the numbers but consider the results if they land exceeding the manufacturers design limits and they crash? The lawyers would have a heyday. Add to that the fact that this aircraft is already in an 'emergency'.

I guess if I were piloting and I had to land heavy, I'd do the best my skill could muster but I wouldn't like it! Fortunately I don't have a commercial license and private aircraft are far less at risk. Nonetheless, I prefer not to land heavy, even in a four-seater if I can avoid it. LOL!

One additional thought. With an engine out, at max weight it will be more difficult to do a go-around if something occurs to force an abort of the landing.

[epmi314]

I understand the 747-400 to have a fuel capacity of 57,285 US gallons or 216,840 liters. Fully loaded that is about 375,000 US pounds of fuel or over 170,000 kilograms of weigh. This means a fuel dump can reduce the overall weight of the craft but nearly on third. Not all planes have the ability to dump fuel but as a matter of caution I guess it makes sense to do so when possible.

[epmi314]

Perhaps, we shoud stay on the ground and drive! Riskier statistically but at least you are in control behind the wheel!

[FrankMi]

I understand the 747-400 to have a fuel capacity of 57,285 US gallons or 216,840 liters. Fully loaded that is about 375,000 US pounds of fuel or over 170,000 kilograms of weigh. This means a fuel dump can reduce the overall weight of the craft but nearly on third. Not all planes have the ability to dump fuel but as a matter of caution I guess it makes sense to do so when possible.

Hi Scott, you are correct, the fuel jettison option is expensive and not available on many commercial airliners. That leaves the option of flying in circles for several hours to burn fuel or land heavy. The pilot must take all the factors into consideration in making his decision.

Fuel Jettisons are usually rare but this was the second time it occurred in Detriot in the past month!

http://www.youtube.com/watch?v=ZPhzn4jjDnE

[Colin Southern]

There is certainly some safety margin in the numbers but consider the results if they land exceeding the manufacturers design limits and they crash? The lawyers would have a heyday.

I suspect that this is a significant part

Add to that the fact that this aircraft is already in an 'emergency'.

The dreaded 3-Engine approach

I guess if I were piloting and I had to land heavy, I'd do the best my skill could muster but I wouldn't like it! Fortunately I don't have a commercial license and private aircraft are far less at risk. Nonetheless, I prefer not to land heavy, even in a four-seater if I can avoid it. LOL!

We used to be landing weight restricted on the Seneca; off memory the given reason was the strength of the wing roots, which (I guess) is what prompted the thoughts above; in reality it wasn't a "real" problem, so long as the landing was smooth (we didn't have fuel dump facilities). Having said that, the Seneca was a "challenge" to land at the best of times (usually about 3 microseconds between getting the nosewheel on the ground and the tail stalling)!

One additional thought. With an engine out, at max weight it will be more difficult to do a go-around if something occurs to force an abort of the landing.

Yeah - although, again, on a 747 it's not as big a deal as losing 1 engine on a light twin; the 747 can actually stay aloft on just 1 inboard engine, although not al MAUW. I fondly remember my first twin engine rating; the irony is that most of the first 5 hours is spent on 1 engine, as instructors constantly fail engines in every possible scenario. We usually still managed about 300 fpm climb in an asymetic go-around though.

[Colin Southern]

I guess it makes sense to do so when possible.

Although ... I remember how Swissair 111 delayed landing whilst they dumped fuel during an emergency; only problem was, they were on fire at the time. They all died. I've had this conversation with several heavy metal piolts, and the general consensus is - if one is really stacked up against the odds - "to heck with landing overweight".

[Colin Southern]

Perhaps, we shoud stay on the ground and drive! Riskier statistically but at least you are in control behind the wheel!

Statistically, the most dangerous part of commercial aviation is the drive to the airport!

[epmi314]

Statistically, the most dangerous part of commercial aviation is the drive to the airport!

Agreed Statistically!... Not having aviation experience myself I concede to Google and those who have more experience with the matter.

[Colin Southern]

Agreed Statistically!... Not having aviation experience myself I concede to Google and those who have more experience with the matter.

Pilots used to joke that aviation was 99% boredom, and 1% sheer terror! (which I might add I pretty much agree with!)

[epmi314]

Pilots used to joke that aviation was 99% boredom, and 1% sheer terror! (which I might add I pretty much agree with!)

That is well put!

[Colin Southern]

That is well put!

Pretty true too I think ... there's just nothing like the feeling you get when you select gear down and only get two green lights - or look out at a spinner with about 3/4" vibration when I have about 90 prop blades a second going past my left knee about 18" outside the cockpit - or see a trickle of oil running from the back of an engine when your 50 miles out to sea - or have a hydraulics failure so that I can't retract the gear (knowing that it won't fly on just 1 engine with the gear down) - or ... nah, that's enough to scare you for 1 day!

[arith]

I never flown in an airliner; now I don't want to.

[Nicola]

perhaps we may consider also the risk of an explosion during a emergency landing, and it should be a big bang for a plane of that kind full of fuel. not the best thing in a crowded airport

[Colin Southern]

perhaps we may consider also the risk of an explosion during a emergency landing, and it should be a big bang for a plane of that kind full of fuel. not the best thing in a crowded airport

Hi Nicola,

Not really - they're still landing with 2/3 of the fuel they took off with (assuming they return soon after taking off). Personally, I think of emergency landings as something that's a real emergency (engine on fire, 1/2 wing fallen off etc), whereas a lot of the (so-called?) emergency landings are more what I would call "sensible / precautionary" landings (eg 1 of 4 engines shut down) (ie a "better safe than sorry" approach) (and nothing wrong with that I might add!).

I've had several instances when I've been flying where I didn't have a positive indication of landing gear being down and locked - or no brakes - but I've never actually declared an emergency (and thus had ambulances and fire engines waiting). In reality it's often not as serious as it sounds; eg with the landing gear you can actually hear it come down and lock - so a quick fly by the tower (who have binoculars) is all the confirmation that's needed - and the runway is long enough to not require brakes anyway (it just makes turning difficult if it's only a single engine aircraft).

[Donald]

Perhaps, we shoud stay on the ground and drive! Riskier statistically but at least you are in control behind the wheel!

Or travel by more environmentally friendly transport and save the planet (sorry, Frank. I know you disagree with me).