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Bruce
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747 Fuel Dumping Question

Fri Dec 03, 2004 3:11 am

There was a discussion on the civil forum about this article but i am posting here a tech question. It says that the guy was ordered to write an essay on the environmental damage of dumping 6,600 tons of fuel into the ocean which is what the plane had to do to safely land in ANC.

This was a NWA 747 enroute NRT - DTW.

Well, Alaska is nearly halfway thru the flight. Why would you have to dump so much fuel at that point? I thought fuel dumping was done if you had to unexpectedly land near the beginning of a long flight when you are too heavy. But by the time this plane gets to Alaska, it should have burned up a good amount..... even with a full pax load it should not be over MLW, right?

and 6,600 tons seems like a high amount of fuel anyway.

bruce
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SlamClick
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RE: 747 Fuel Dumping Question

Fri Dec 03, 2004 5:34 am

That number has to be way off. 6600 tons is 13,200,000 pounds. That is more than the combined weight of fifteen 747s.

?

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HaveBlue
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RE: 747 Fuel Dumping Question

Fri Dec 03, 2004 6:32 am

Probably 6,600 gallons, which is roughly 39,600 lbs.
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SlamClick
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RE: 747 Fuel Dumping Question

Fri Dec 03, 2004 7:39 am

I agree, HaveBlue that is a much more reasonable figure.

Whatever the correct number (I could not find the other thread) it is easy to imagine the need to dump.

NRT to DTW is going to burn quite a lot of fuel and you need to keep in mind that the flight was planned to arrive at destination with enough fuel to meet flag rules for alternate, reserve, and any other needs. So by the time it is in the vicinity of ANC it is still pretty heavy.

I'm not a 747 pilot and don't have actual numbers but there are some generalities that need to be considered here. If the pilots had a problem that required them to go to the nearest suitable airport (or some such rule) while it is pretty serious, it does not wipe out all the other safety rules. They cannot begin an approach into ANC at a weight that would not permit them to do a missed approach or a rejected landing with an engine inoperative. Fuel dumping sees a likely option under the circumstances.

I'm curious who it was that had the power to order this pilot to write an essay on anything. I believe that I'd have changed the rules a bit and written one on the environmental damage caused by dumping ALL my fuel plus three hundred dead human bodies in the ocean.

It is called "captain's emergency authority"
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A350
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RE: 747 Fuel Dumping Question

Fri Dec 03, 2004 7:54 am


I'm curious who it was that had the power to order this pilot to write an essay on anything


SlamClick,

It was NOT the pilot who has to write the essay but the AGGRESIVE PASSENGER. And there is a difference if a fuel dumb is done because of a medical emergency or simply because a drunken person is getting aggressive.

"Sahutske.... He also was ordered to write a minimum 15-page essay on the environmental impact of dumping 6,600 tons of fuel into the ocean, which the plane had to do to safely land in Alaska."

A350
 
PhilSquares
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RE: 747 Fuel Dumping Question

Fri Dec 03, 2004 8:53 am

One of the problems is depending on the airline, the philosophy on overweight landings varies. For instance at some airlines, if you're over the MLW and have to land, all you have to do is make a logbook write up stating an overweight landing was performed. At some other airlines, such as NWA, you need to declare an emergency to do an overweight landing.

In either case, it's no big deal. A simple visual inspection is conducted by MX looking for signs of a hard landing. Theoretically, the aircraft is capable of landing at it's MTOW 870,000, so a landing in the vicinity of, in this case 670,000lbs would be no big deal.

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cloudy
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RE: 747 Fuel Dumping Question

Fri Dec 03, 2004 3:25 pm

My guess is the maximum landing weight is not only based on the effects of one landing - but of the effects of thousands of landings. Landing over the maximum landing weight once would usually not be a big deal, but if it were done for every landing it would put an unnacceptible stress on the airframe.

So the main reason airlines(and regulatory agencies) don't exceed maximum landing weight routinely is to avoid putting excessive stress on an airframe. Such stress could cause the airframe fail unnexpectedly at a later point, or require expensive repairs. Usually, the safety of the overweight landing itself is not in question.
 
widebodyphotog
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RE: 747 Fuel Dumping Question

Sat Dec 04, 2004 9:25 am

Depending on the speed and altitude during the fuel dump, the fuel would evaporate before it ever reached the surface of the ocean. The environmental impact would be negligible unless the aircraft was flying below about 2500', and 175kts.

-widebodyphotog
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A350
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RE: 747 Fuel Dumping Question

Sat Dec 04, 2004 10:49 am

Depending on the speed and altitude during the fuel dump, the fuel would evaporate before it ever reached the surface of the ocean. The environmental impact would be negligible unless the aircraft was flying below about 2500', and 175kts.


I doubt this, because Kerosene is a heavy oil and does not evaporate in total. Maybe you produce an aerosol, but not vapour. That means the Kerose gets in the biosphere, diluted, but not evaporated.

A350
 
QantasA332
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RE: 747 Fuel Dumping Question

Sat Dec 04, 2004 11:08 am

Believe it or not, A350, jet fuel does indeed evaporate. Before the 'raw' fuel is dumped, pumps basically turn it into very fine fuel droplets which, when in the atmosphere, evaporate relatively quickly.

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widebodyphotog
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RE: 747 Fuel Dumping Question

Sat Dec 04, 2004 11:51 am

Thanks QuantasA332

Exactly right. Releasing fuel into the high speed airstream atomizes fuel into vapor and it dissipates suprisingly rapidly. Kerosene is relatively heavy but still has only 81% of the density of pure water.

widebodyphotog
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PhilSquares
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RE: 747 Fuel Dumping Question

Sat Dec 04, 2004 12:06 pm

On the 744, Boeing recommends a minimum altitude of 6000' with flaps up. At that altitude and airspeed, the fuel will vaporize long before it could hit the ground.
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rendezvous
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RE: 747 Fuel Dumping Question

Sun Dec 05, 2004 6:51 pm

In a situation where a landing is to be made, say, with a main gear failure, would it not make more sense to dump as much fuel as possible to reduce any fire that subsequently ignites on landing?
 
PhilSquares
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RE: 747 Fuel Dumping Question

Sun Dec 05, 2004 8:09 pm

In that situation, it makes more sense to dump fuel to reduce weight. With a substantial weight reduction, you won't have any worries at all.
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LHSebi
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RE: 747 Fuel Dumping Question

Sun Dec 05, 2004 11:07 pm

Philsquares,
Do you mean that with a weight as close to the empty (fuel) weight as possible, the Fuselage could support the weight if it would have to do a belly landing for instance?

Sebastian
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PhilSquares
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RE: 747 Fuel Dumping Question

Mon Dec 06, 2004 12:35 am

No. With a wing or body gear retracted you have reduced braking. Therefore, you'd want to reduce your gross weight. Landing with all wing or body gear retracted is no real big deal in the 747.

My response was directed at reply 12. There has never been a case of a 747 that has had body and wing gear failure. In addition, at typical landing weights, all the fuel is contained in the wing tanks.
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wingnutmn
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RE: 747 Fuel Dumping Question

Fri Dec 10, 2004 2:41 pm

Another question about 747's and dumping fuel....How long would it take to dump 6600 gallons of fuel first, and then how long would it take to dump enough fuel if you lose an engine on takeoff at MTOW to get you below MGLW? (this would be about 200,000 pounts)

WingnutMN
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HAWK21M
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RE: 747 Fuel Dumping Question

Fri Dec 10, 2004 3:24 pm

What is the rate of Fuel dump,can it be controlled or is it Fixed open/close valve.
Has there been any occasion when the min 6000ft altitude had been crossed during dumping.
regds
MEL
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PhilSquares
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RE: 747 Fuel Dumping Question

Fri Dec 10, 2004 6:40 pm

The dump rate with 6 pumps going is 6000lbs/min. And the 6000' is just a recommendation for a non-emergency dump. In an emergency, you can dump at any altitude, but if it's really low, the fuel might not vaporize.
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