UAL395 and LH404 fuel dumps and diversions

Trailblazer

Moderator
Staff member
United Airlines flight 935, a 777 dumped fuel over the UK today before returning to Heathrow.






 
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Pete Tar

Senior Member
And the length. Is there any fuel dump picture that doesn't crop the end of the fuel trail?
Is the fuel crystallising momentarily?
 

skephu

Senior Member
And the length. Is there any fuel dump picture that doesn't crop the end of the fuel trail?
Is the fuel crystallising momentarily?
In this video you can see two planes dumping fuel. At 0:16 the camera zooms out, and it appears the trails are rather long.

JP-8 fuel can crystallize below -47 °C.
 

deirdre

Senior Member
but fuel dumps dont happen at normal plane cruise altitudes right? so they are alot easier to see longer.
 

Leifer

Senior Member
http://c141heaven.info/dotcom/tall_tales/aviation_fuels.pdf
Exonn/Mobil avgas 100 says the freezing point is -58* C
http://www.exxonmobil.com/China-English/GFM/PDS/GLXXENCMFEMAvgas.aspx

As far as I know, the higher the flash-point, the more a solvent "attracts" water.
This is just a guess, based on my use of acetone and ISP (isopropyl alcohol)...there may be a name for the effect....I'll look.
EDIT: ....HYGROSCOPIC

Although, I'm not certain avgas (kerosene) is "miscibilic"...meaning it will not readily mix with water in it's room temp state. Alcohol (methanol) will though.
....and is why engines struggle or fail when water is in the fuel.

...and is why firefighters don't use water on a "non-miscible" solvent fire. But they may use water simply to cool the fire's heat,....and then use special "foams" to kill those solvent fires.
 
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Trailspotter

Senior Member
Two photos taken at the moment when the plane turned back. Perhaps it was before the fuel dump began, as it looks like an ordinary short contrail.


Source

A photo from the plane:

Source
 
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Ross Marsden

Senior Member
especially on polar routes during the winter.
(I realise this is a quote from an external source.)

I don't think the temperature at cruise altitude in polar regions is all that cold, given the relatively low height of the tropopause (above which the temperature ceases decreasing with height, or even increases).
 

TWCobra

Senior Member
(I realise this is a quote from an external source.)

I don't think the temperature at cruise altitude in polar regions is all that cold, given the relatively low height of the tropopause (above which the temperature ceases decreasing with height, or even increases).
The only time fuel temperature got close to -47C for me was over Russia in winter. Outside Air Temp was about -70C.

Just moving through the air at the speeds we do increases the airframe temperature by 20-25 degrees.
 

Trailspotter

Senior Member
Coincidently, there was another fuel dump over the UK with Lufthansa LH404 B747 to JFK having been diverted to Manchester:

Source

Source
 
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deirdre

Senior Member
Just moving through the air at the speeds we do increases the airframe temperature by 20-25 degrees
so the plane warms the contrail area up 25 degrees? maybe a better question is... whats an "airframe temperature"?
 

TWCobra

Senior Member
TAT or total airframe temperature is the actual temperature of the the aircraft skin as measured by various sensors. We use it mainly to determine when to switch the anti-icing devices in the engines and on the wings.

SAT is static air temperature. On the ground the two are the same. Once we start moving at higher speeds there is a gap in them caused by air friction. Eventually at high Mach Numbers TAT gets to be around 25C warmer than SAT. This keeps the fuel warmer.

The indications are bottom left on The lower screen in this picture. ISA shows the deviation from the Standard Atmosphere temperature.

image.jpg
 

TWCobra

Senior Member
That bottom display also shows the fuel system. If you look closely you can see fuel temperature indications along the bottom of the tank indications. The coldest fuel is always in the outer tanks during flight. Something to do with airflow and the tanks are thinner at the wingtip.
 
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