View Full Version : Fuel Freezing Temperature Question

11th Sep 2007, 15:46

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 ?


11th Sep 2007, 16:04
is this temperature is SAT or TAT ?

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.

11th Sep 2007, 16:25
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.. ?


11th Sep 2007, 16:54
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.

11th Sep 2007, 17:03
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'!

11th Sep 2007, 20:47
it is very clear now :ok:

thanks every one .

11th Sep 2007, 23:06
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. :)

Tight Slot
11th Sep 2007, 23:32
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!!!

12th Sep 2007, 00:49
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.

12th Sep 2007, 00:50
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!!


12th Sep 2007, 02:19

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.


12th Sep 2007, 08:21
Thanks a lot guys. Point taken.

12th Sep 2007, 11:31
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.

12th Sep 2007, 12:43
Some info that might be of help in link below.


12th Sep 2007, 13:27
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!!

Right Way Up
12th Sep 2007, 14:48
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.

12th Sep 2007, 16:02
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.

12th Sep 2007, 17:39
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.


12th Sep 2007, 22:49
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 -74C), and had to descend. until then I never knew, that there was a temperature too low for the aircraft itself...

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.

13th Sep 2007, 12:32
we were outside the certified operating envelope for the aircraft

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

13th Sep 2007, 13:28
Interesting reading, coldest ground temp, i've ever flown in was -48c. was colder at altitude w/ a density altitude at t/o of -7000' had the heater go u/s with an hour to go, had to be lifted out of the cockpit! http://www.boeing.com/commercial/aeromagazine/aero_16/polar_story.html

13th Sep 2007, 14:51
another question : does the fuel tanks have heater in them ( i fly A320 ) ?

13th Sep 2007, 15:39
Read your FOM

13th Sep 2007, 21:44
It is not mentioned in the FCOM

14th Sep 2007, 00:26
In the Fcom you'll only find thatSome of the fuel supplied to each engine goes from the high-pressure fuel line in that engine, through the integrated drive generator (IDG) heat exchanger (where it absorbs heat), to the fuel return valve, and back to the wing tank.This is to serve cooling the IDG.
Recirculation of fuel to the fuel tanks according to the engine oil temperature, the fuel system configuration and the flight phase
In the old generation Aircraft like the B727 For example you had fuel heater switches.

14th Sep 2007, 00:47
So there is no fuel heater in the tanks...the fuel get warmer by the IDG absorbed heat.

thanks for shedding the light on this issue.

Mx Reverse
16th Sep 2007, 20:50
We operated a nightly round trip from central Europe to Yerevan, Armenia (EVN/UDYZ) in fall 2005. SATs were around -70C to -71C (at FL350 if memory serves me right).

Due to fuel shortage we departed home base with a full load of fuel (19,3 to) on a lightly loaded A319. Shortly prior to TOD we got the Advisory Condition that the left outer tank was at -41C. So we descended just a couple of minutes earlier.

During tournaround we uplifted only about 3,500 kgs so trouble came back about an hour after reaching cruising altitude. Lower levels were all blocked an Rostov ATC was not really cooperative (probably not understandig WHY we wanted to descend).

So we contacted our trouble-shooters (engineering dept) via acars and asked if there were any objections against opening the fuel x-fer valves to mix the 2x 700 kgs outer tank fuel with the significantly warmer inner tank fuel. They gave us the go-ahead which saved the poor controller a mayday-call and an unapproved descend, which we would have done at -44C in any tank, as our book gives a Limitation to keep fuel temp 3 degs above freezing point.

Good Thing about the Wing A/I, never thougt about it. Maybe switching on some ovens in the galleys might work as well.

Regards, MAX

16th Sep 2007, 21:07
You said It is not mentioned in the FCOM

The information you need is CLEARLY available in FCOM's. Start at 1.28.10 page 6 and keep reading !

I also mentioned that this is very basic stuff covered in the groundschool. If kuwait340 does have an A320 rating he really should know the basics, and at least where to find it in the fcoms.

17th Sep 2007, 16:18
Thanks Every One For Your Kind Reply's.

18th Sep 2007, 02:47
(a) we have two useable choices with inappropriate post content -

(i) ban the user .. usually overkill
(ii) edit the material .. which fixes itinerant problems

(b) time and workload doesn't permit too much in the way of admin niceties like exchanges with individual posters on such matters

(c) the mods determine whether content is OK or not

.. that's the way life is, I'm afraid ....