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Sesquashtoo

With this spate of very cold weather ...I have always wondered about Aviation Fuel...

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Hey everybody,

 

With the spate of very cold, Arctic air that has gripped most of North  America the past 6 weeks, and when going to work, and seeing many transport trucks on the side of the highway(s), and knowing some of them must have gelled fuel (diesel will turn to something like Vaseline in very, very cold weather, and even with fuel conditioners at times)....how is it, that a wing, full of aviation-grade jet fuel,can stay fluid enough to pass through the lines and on to the turbines, at what must be incredibly low temperatures that those fuel tanks will endure, at the high FL's, due to ambient, as well as wind-chill elements in play?!?!?!?!?

 

So, my question is, to anybody that has professional experience regarding this question....what do they do to treat Jet fuel, (that is similar to diesel fuel) to actually be able to flow from the wing tanks, to the turbines?  I never really thought about this, even as a flight passenger, before seeing all these trucks to the side of the highways this last many weeks!

 

We all worry about the commercial pilot's fatique, skill sets, or aviation electronics failures within the cockpit environment...but had many of us, have ever wondered about fuel starvation, as we gaze out over that wing at FL350?!?!?!?!??

 

I'd love to know...how does the Jet fuel...stay transient at such extreme cold environments of Winter flight ops.....for commercial traffic....

 

Jeez....

 

Ses

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They mix icing inhibitors into the fuel. Minimum fuel temperature limitations are around -54c. Although this hasn't kept the underground fuel lines at some airports from freezing this season.

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I remember my father telling that one time on a flight from EHAM to PANC with a KLM DC10, temperature dropped below -55C and so they had to pump fuel from one tank to the other and back to prevent it from freezing.

Maybe mixes have changed nowadays but it is still something pilots keep an eye on.

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so they had to pump fuel from one tank to the other and back to prevent it from freezing.

 

-------------------------------

 

"Oh LORD!"  :unsure:

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Friction caused by the air flowing over the wings creates some heat, so temps in the wing tanks will stay a bit higher than the outside air temp.

 

But if fuel temps drop too much, and pilots can't compensate by circulating fuel, they have to look for higher OAT (that is, go to lower flight levels).

 

http://aviation.stackexchange.com/questions/2185/how-do-aircraft-keep-the-temperature-of-the-fuel-tanks-above-freezing-point

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Friction caused by the air flowing over the wings creates some heat, so temps in the wing tanks will stay a bit higher than the outside air temp.

 

But if fuel temps drop too much, and pilots can't compensate by circulating fuel, they have to look for higher OAT (that is, go to lower flight levels).

 

http://aviation.stackexchange.com/questions/2185/how-do-aircraft-keep-the-temperature-of-the-fuel-tanks-above-freezing-point

Olli, thanks for that link, just came from it...and man, does it explain in detail!   Feel better, already.....

 

Mitch

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Read the report on the BA38 crash.  You will learn more about cold fuel then you ever wanted to know (at least, on the 777).

 

scott s.

.

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The designers thought about this problem.  Some planes have a heat exchanger for the hydraulic system in the fuel tank.  Most planes use the fuel to cool the engine oil. 

 

There are also limitations on how cold TAT/RAT can get. Usually if its too cold, you can speed up or descend.  You only tend to run in to the limit if your plane is artificially slowed due to some mechanical issue during the winter.

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here are also limitations on how cold TAT/RAT can get.

----------------------------------

 

I wonder, is there an alarm that the flight crew can set for the limit that must not be reached, that goes audible in the cockpit?

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environments of Winter flight ops.....for commercial traffic...

Mostly it is only polar (or flights that operate in proximity of polar regions) routes that are affected. 

 

Not sure about audio alarm but crew gets all kind of warning messages on their EICAS/EFIS screen.

 

If fuel temperature drops below -35 C it automatically triggers ACARS messaging, this way airlines can actually

monitor low fuel temperatures in real time for their flights. Collecting such data helps dispatchers to plan

for such low fuel temp routes.

 

This is a fairly detailed article on the subject.

 

https://airlinesafety.wordpress.com/2014/04/03/cold-fuel/

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The fuel temp in tank inflight will decrease toward the TAT (total air temperature) which is quite a bit higher than SAT (static air temperature) due to compression effect at high speed. The TAT inflight at cruising level on the 777 is typically around 20c higher than SAT. So typical with fuel freezing point at a default setting of -37c we may get an EICAS caution msg at ~ -60c or more directly when the TAT indication on the upper EICAS shows -37c after a few hours into the flight then sooner or later we will expect to see the fuel temp low msg. On the a330/340 the fuel low temp ecam msg comes out at fixed temp value of -37c to -40c depends on fuel tanks, and unlike the 777, the limit can not be modified on the airbus.

 

For a normal Jet-A1 fuel the freezing point is -47c and JetA is -40c. The best fuel for cold weather is the Russian TS-1 which theoretically has a freezing point of -60c (while the limit of -50c is often used). For 777 we are allowed to modified the fuel temp from default -37c to either "the actual fuel freezing point + 3c" or if other fuel is used i.e Jet A1 -47+3=-44c so as to delay the trigger of the fuel temp low msg to a lower temp which sort of more accurately reflects the actual condition of the fuel.

 

Having to go over the pole at least once a month, it is so far not too much of the problem. Because the actual freezing point for JetA provided by the fuel supplier at let say JFK or ORD is usually around -43-45c. And the lowest fuel temp I have seen so far is -40c over northern Siberia, touchwood. Flights from Europe. Asia and Russia will always have jetA1 or TS1 uplifted so it's practically never an issue.

 

Like someone had already mentioned above if in case it happens either speed up or descent. I prefer speed up for a bit so that I will be able go home a bit sooner at the expense of may be 200kg-500kg extra fuel depends on how long I need to keep the speed up. On the 777, every 0.01 Mach will increase the TAT to approximately 0.5-0.7deg.

 

Hope it helps.

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The fuel temp in tank inflight will decrease toward the TAT (total air temperature) which is quite a bit higher than SAT (static air temperature) due to compression effect at high speed. The TAT inflight at cruising level on the 777 is typically around 20c higher than SAT. So typical with fuel freezing point at a default setting of -37c we may get an EICAS caution msg at ~ -60c or more directly when the TAT indication on the upper EICAS shows -37c after a few hours into the flight then sooner or later we will expect to see the fuel temp low msg. On the a330/340 the fuel low temp ecam msg comes out at fixed temp value of -37c to -40c depends on fuel tanks, and unlike the 777, the limit can not be modified on the airbus.

 

 

This adds to the interesting discussion, and thank you for your contribution.   I take it you 'drive' for a living...so I ask you...what then, is your take on B.A. flight 38, from Beijing  to Heathrow....and the formation of ice crystals at 700 ft almost above the threshold to the runway? How then, could this have been even possible?!?!??  That was their finding to bring down the 777...ice crystals blocking the flow to the engines....as to their route to Heathrow, over-flying parts of Siberia.

 

 

This is a fairly detailed article on the subject.

-------------------------

 

A great link for reading...and thank you for posting!

 

Mitch

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How then, could this have been even possible?!?!??  

I suggest you read the final report, it is explained 'how' in fair detail with a caveat that this is a very difficult topic and not all fuel icing events are well understood even today. The report mentioned that basic fuel icing research was done over 50 years ago and no one has returned to the subject ever since but as this accident showed there is need to do more.

 

Complex physics was at play (and things like vibrations and/or rate of fuel flow as well as the shape of fuel feed lines all were factors) and in fact this 'ice formation' blocking entrance of fuel to FOHE (fuel-oil heat exchanger) had nothing to do with its flight over Siberia - this aircraft was not exposed to some abnormal low temperatures. The report makes clear that cold soaking during flight over Siberia was not a factor in this accident. Rolls Royce was asked to redesign the inlet area to FOHE.

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To put the BA accident in simple term, it wasn't the fuel which turns into ice and blocked the FOHE inlet, it was the water content which was suspended in the jet fuel that turned into ice.

 

Although the refueler always do a water check at during refueling stage, it's inevitable that some water content is suspended in the fuel. Imagine 0.1% water content of 100Tons of fuel is still a substantial volume of water (~125L of water).

 

When pure 100% jet fuel temperature approaches the fuel freezing point, it turns into a gel type of "liquid" which makes it harder for the fuel pump to pump it towards the engine, until a point where it turns into a gel completely and exceeds the fuel pump capability.

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