Fuel Freezing Temperature Question
 

Hello....

as you may know...the Jet A-1 freezing temperature is -47C.

is this temperature is SAT or TAT ?

and i remember one pilot told me if i approach this temp...i must either descent to a lower level or increase the speed.

any suggestion ?

thanks

Neither. It's the fuel tank temperature.

TAT is often less than fuel freezing point in the cruise. The TAT effects the rate at which the fuel cools down but other factors Fuel/oil heat exchangers hydraulic pump cooling etc also influence the cooling rate.

However if the fuel temp approaches freezing point the only thing you can do is increase TAT ie fly faster or lower.

thanks for your reply...

the aircraft i fly has in tanks fuel temp indication...

but what if i don't have ...what will be the case.. ?

thanks

hiya,
a bulletin by boeing suggests that in case of indication failure maintain the TAT at least 3 degrees above the fuel freezing point as a conservative measure.

It will still be the Fuel Temp. How cold it get depends on the TAT, the temp it started at, how thick the wing is, where the fuel tank is, what it is made of, how long you have been flying etc etc but..it will still be not the TAT or SAT but the 'FaT'!

it is very clear now :ok:

thanks every one .

Having flown regularly 18 hour nonstop flights vie the North Pole and North Pacific, I've never been even close to fuel freezing temperature. Sleep well my friend. :)

Fuel freezing is more prone to near the tropics as the troposphere is higher there and thus much more cold. Had very low fuel temp on a Barbados - london aroung April this year at FL400. Had to speed up, hey ho, got home quicker!!!

There was a writeup awhile back on an MD11"i believe" over Russia that had fuel tank temps too low. Due to the language barrier they were unable to descend, the F/O showed good systems knowledge and activated the wing anti ice, dumping hot bleed air to the LE, the temps slowly rose.

Fuel temperature.
 

Capt. Bee,

You have been fortunate. It is not a frequent occurence, but I left Calgary for London with an L1011, and had to go down over Greenland as it got too cold in the tanks.

It was minus a lot at departure, and the fuel was also very cold when loaded so it all added up. When all the holes line up you are in trouble!!

Speedbird48.

Speedbird48,

I have to agree with you, I've seen the fuel temp get low enough to need to speed up a couple of times over the years. It happened on the LAX direct SYD flight in a B747SP. We were able to accelerate and keep things warm enough to continue at our present level.

Regards,
BH.

Thanks a lot guys. Point taken.

Please correct me if I'm wrong

I don't BELIEVE there has ever been an aviation accident attributed to freezing fuel in flight!!! (Someone may be able to shed more light....)

The freezing temperature is a guide line and may vary depending on where the fuel is "picked up". Some operators use guidleines such as using the most conservative figure for at least 3 "fills" if you know the actaul freezing temp...

I don't believe too much stress needs to be placed on approaching your 3 degree buffer. The freezing temperature refers to waxing in the fuel which still allows normal operation and no immediate cause for alarm

Increasing speed needs anticipation as it has a slow effect on increasing temperature. You may need to descend, in some cases by several levels to stab the fuel.

Some info that might be of help in link below.

http://www.airbus.com/store/mm_repos...6_low_fuel.pdf

Folks,
The best (worst) temp. I have come across was over Russia in winter, we were outside the certified operating envelope for the aircraft, and apparently quite close to the lowest temperatures ever recorded at these altitudes ( around FL350). Memory ain't what it used to be, but whatever ISA - limit is in the B747-400 Limitations, it was about 16 degrees colder.
Average temperature profiles below 60S and over the Antarctic also seem to come in somewhat colder than the Standard Atmosphere.
Tootle pip!!

I remember the issue for our fleet used to be leaving the US as they only had Jet A fuel with freezing point -40 degrees. I remember seeing a writeup about assumed freezing point with mixed fuels. Safest assumption was to use the worst case fuel freezing point.

The generic fuel freeze temperature for JetA is published as -40C compared with -47 for JetA1. Any time I have to fly the polar routes from the USA my company pays for the ACTUAL fuel freeze temperature analysis for the fuel uplifted because it is JetA. They take three samples, one at the beginning of refuelling, one in the middle and one at the end. The worst case is then used as the ACTUAL fuel freeze Temp for that flight. The worst case I have seen is a freeze temperature of -45C and I have never come close to this yet.

Actually it is not a fuel freez temperature, it is the temperature where certain additives form clots or flakes and may clog the nozzles, just like Diesel ina car.

Nic

I encountered the same as LeadSled, over Russia in the wintertime, from MUC to NRT, flying in the dark over northern Russia. We went outside the environmental envelope (below -74°C), and had to descend. until then I never knew, that there was a temperature too low for the aircraft itself...

edit:
Actually this thread is about fuel...

I don't think the fuel freezes, it just clots and clogs your nozzle, like a Diesel engine in a car.

Why? Please elaourate or do you often fly outside of the aircraft's certified limits?