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Fuel Off Of Wingtips?

Thu Jun 17, 2004 6:07 am


On another forum I participate in, a shot was posted showing what was believed to be fuel coming off of the wingtips.

This is qouted from the post:

"the Captain reported fuel ventilating out of both wings just before pushback. This resulted with fuel all over the apron but the Captain refused to wait any longer and by the sounds of things, just wanted to depart. A touch blurry due to the jet wash, but you can clearly see fuel gushing out of the wings on rotation!"

To me, something did not seem right. Now I ask, what is coming off the wings, why it would happen, and why the pilot was permitted to fly. link

Your thoughts?

Christopher Ryan

[Edited 2004-06-16 23:12:00]
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RE: Fuel Off Of Wingtips?

Thu Jun 17, 2004 6:54 am

Fuel will expand as it warms up, so if the aircraft was filled up and topped off ...Say before the sun came up, then departed under a warm sunny sky this is what will happen. I can think of a few personal cases when I was jumpseating during a cross country ferry flight and as the air warmed up, the aircraft began venting fuel. This is the reason jet fuel is messured in Lbs/Kg, and not Gals/Ltrs. The weight will not change, but the volume will.

[Edited 2004-06-16 23:57:49]
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RE: Fuel Off Of Wingtips?

Thu Jun 17, 2004 7:01 am

The situation although common is not normal.

The pressure fueling system on an large jet AC incorporates an auto shutoff feature that closes the fueling valves when the tanks are full. This can be overridden to accommodate a bad sensor(falsely seeing fuel therefore closing the fueling valve when the tanks aren't full) but then the fueler must be careful to not overfill. You can also override the auto shutoff to pack a few more gallons in the tank. This is not legal but does happen.

If the pilot knew he had fuel leaking he should have written it up in the log book and let MX check it out, unless he knew they had packed the tanks and then there would be no point in contacting MX as there is nothing wrong with the plane.
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RE: Fuel Off Of Wingtips?

Thu Jun 17, 2004 10:14 am

On the 747 there is a "surge" tank located at the tip of each wing. This tank is used to hold any fuel that comes from the tanks as the fuel expands. If the aircraft was fueled when the temperature was cool and then sat there for several hours in the sun, the fuel would expand. The tanks are vented to allow for expansion and the excess fuel then drains into the surge tank.

If the surge tank is full then as the aircraft rotates fuel will vaporize and exit the surge tank through the vent box located at the wing tip.

There is nothing really wrong with this and the system is operating as it was designed.
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RE: Fuel Off Of Wingtips?

Thu Jun 17, 2004 11:53 am

Philsquares: Sounds about right, but that results in a loss of fuel. Seems to be an indirect form of fuel-jettison. Do they compensate for this when fueling up, and put a little extra in there when they know that there's time for the juice to expand and be released?
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RE: Fuel Off Of Wingtips?

Thu Jun 17, 2004 12:19 pm

The fuel is calculated by weight, not by volume. Therefore, the total weight in the tanks really doesn't change by any measureable degree. The total quantity in the ventbox/surge tanks is really quite small and in the bigger picture really doesn't amount to much.

Hope this helps
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RE: Fuel Off Of Wingtips?

Thu Jun 17, 2004 1:59 pm

We had some problems with the overfill protection system in older jumbos. It operates through float switches in the surge tanks (were the fuel tank vent lines lead to) and either the system didn´t shut the fueling valves when a tank was full or it shut too early, so that we had to override the system to get the correct fuel quantity on board. In the end (after a few fuel spills on the ramp) we had orders to have a mechanic to manualy fuel the planes, with the automatic switched off.

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RE: Fuel Off Of Wingtips?

Thu Jun 17, 2004 8:30 pm

I personally find it hard to believe that the captain would TO with fuel coming out of the wing vents. I know when the VTO were mis calibrated and we dumped fuel on the ramp it was a HUGE deal and the airport authority even had the fire trucks standing by. Something seems fishy to the whole story.

but hey I do not know everything I just like to believe I do.  Smile/happy/getting dizzy
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