outer tank low temp. warning

[dosdogru 3]

i got this warning on my last 2 flights.anything i can do against it?

[Paul_Smith 8]

Fly at a lower altitude where the air is warmer.

[dosdogru 3]

Fly at a lower altitude where the air is warmer.

hm it was at Fl360 which i thought is common for that aircraft...+ the warning keeps on even at approach.

[HenryD 39]

Had this issue yesterday too, at FL350 after maybe 2 1/2 hours in cruise, outside air temperature about -53° C, TAT about -23° C, and fuel was at -47°C. Could it be that the fuel temperature is calculated wrong from the SAT?

During this message flight performance was not affected, but it does not look well if you make pictures or videos with these messages.

Regards

Henry

[Paul_Smith 8]

Are you sure you understand SAT and TAT correctly, and their effects on stuff like fuel? Spend 2 1/2 hours at -53C and you should expect your fuel to freeze. Try it in the PMDG MD-11 (where this is modeled) and your engines will stop.

[HenryD 39]

Are you sure you understand SAT and TAT correctly, and their effects on stuff like fuel? Spend 2 1/2 hours at -53C and you should expect your fuel to freeze. Try it in the PMDG MD-11 (where this is modeled) and your engines will stop.

Never experienced in the PMDG, -53°C in FL 350-FL370 is normal SAT I think (don't beat me if I am wrong regarding the nominations, maybe it is TAT, what I mean is the temperature at a certain place in FL350-FL370 not regarding wind and velocity), the TAT is quite higher cause the aircraft is moving with wind, weight and velocity effect, therefore it is warmer than the SAT. So if fuel freezes at -53° C which is more or less the normal temperature at FL 350-370 than this should be the case in most aircraft which I doubt. I had one time fuel freeze in the PMDG at FL 410 not having loaded the right fuel sort before takeoff.

Regards

Henry

[Catchman86 3]

I have noticed that if I have the wing and engine anti-ice on while flying in air that cold (-50+), I can usually keep the fuel temp in the closer to -20 or -10. I very much doubt any real world applicability here, but I can understand the logic, somewhat. As the leading edge of the wing and fuel/oil interchange in the engine is warmed, some of the heat starts to transfer.

[dosdogru 3]

I have noticed that if I have the wing and engine anti-ice on while flying in air that cold (-50+), I can usually keep the fuel temp in the closer to -20 or -10. I very much doubt any real world applicability here, but I can understand the logic, somewhat. As the leading edge of the wing and fuel/oil interchange in the engine is warmed, some of the heat starts to transfer.

some support would be nice...

[Paul_Smith 8]

some support would be nice...

You are really a lovely person and all those people who say otherwise are mistaken.

Is that the sort of thing you are looking for?

[maddz 737 55]

[dosdogru 3]

You are really a lovely person and all those people who say otherwise are mistaken.

Is that the sort of thing you are looking for?

i know and you are right but the warning still remains and the no support too.

[Paul_Smith 8]

I just had a look at page 50 in the Fuel Systems section of the A320 series on SmartCockpit.com ( - lots of really cool stuff over there - ) and I found this:

It basically says to expect a warning if your fuel is below -40C. Are you saying that your fuel was warmer then -40C and so you should not have got the message? Or are you saying you don't think your fuel should be that cold?

Henry spent two and a half hours at -53 so it is no surprise his fuel cooled to -47, but you never did say what you were doing and telepathy is not my strong suit

[Paul Golding 159]

but you never did say what you were doing and telepathy is not my strong suit

It is mine...............and I can tell what you're thinking when you read through the above.

[HenryD 39]

I just had a look at page 50 in the Fuel Systems section of the A320 series on SmartCockpit.com ( - lots of really cool stuff over there - ) and I found this:

It basically says to expect a warning if your fuel is below -40C. Are you saying that your fuel was warmer then -40C and so you should not have got the message? Or are you saying you don't think your fuel should be that cold?

Henry spent two and a half hours at -53 so it is no surprise his fuel cooled to -47, but you never did say what you were doing and telepathy is not my strong suit

Please read my post above again, I said I was flying in FL 350 at SAT of -53°C, which is absolutely normal temperature at that altitiude, although you accused me later on not knowing about temperatures. But SAT is not relevant in this case, TAT (True outside air temperature) is relevant regarding temperature in the surrounding of the aircraft. And TAT is always warmer (as we are in negative scale in these heights, it is higher) than SAT. The TAT at FL 350 is about -22°C to maybe sometimes up tp -30°C and so fuel inside the aircraft never should get colder than -40°C. This is the normal behaviour of all other aircraft I fly virtually (PMDG 747, MD11 and CS757) and if fuel would freeze when SAT is less -40°C, then no real world airplane could fly at FL350-FL370 because SAT is about -48°C to -54°C at FL350. I further wrote that I once experienced fuel freeze in FL 410, where SAT is about -60°C and TAT can go down to -40°C and more, and that was with the PMDG MD11, here you have the possibility to load two different sort of fuel, one freezes at a lower temperature than the other.

Besides I never experienced this warning again, although I did another longer flight at same altitude and same temperature, my suspicion for now is that it maybe is releated to 3rd party weather programme, in my case ASE. I will report back if this warning comes up again.

Regards

Henry

[Paul_Smith 8]

Sorry Henry, but I didn't accuse you of anything. I asked if you understood the difference and you have just demonstrated again that you don't. TAT is a indication of the effective temperature of your leading edges (useful for judgeing iceing conditions etc.) while SAT is the temp the rest of the surface area is exposed to (useful for fuel freezing etc.).

[HenryD 39]

Sorry Henry, but I didn't accuse you of anything. I asked if you understood the difference and you have just demonstrated again that you don't. TAT is a indication of the effective temperature of your leading edges (useful for judgeing iceing conditions etc.) while SAT is the temp the rest of the surface area is exposed to (useful for fuel freezing etc.).

Then you may have an answer to my question:

This is the normal behaviour of all other aircraft I fly virtually (PMDG 747, MD11 and CS757) and if fuel would freeze when SAT is less -40°C, then no real world airplane could fly at FL350-FL370 because SAT is about -48°C to -54°C at FL350

Regards

Henry

[HenryD 39]

Found the answer myself here:

http://www.flightlevel350.com/forum/lofiversion/index.php/t8799.html

27driver's point about the freezing temperature of fuel. If jet fuel freezes at -40C (actually it will gel) how can you fly in temperatures of -54C in the stratosphere? The answer is that the friction of the air over the plane at speed heats up the airframe. At mach .80 at and above FL360, for example, the friction of the air heats the skin of the plane by about 30C, keeping the fuel in the wings at a safe temperature.

So flying the Airbus at FL350 with mach .78 under normal weather conditions above Europe (SAT between -47°C to -54°C) should never get such a warning unless maybe there is a fault in the warning system.

[Paul Golding 159]

I've never seen this warning and I don't have any weather add-on's installed. Has anyone using the default weather seen this?

[dosdogru 3]

I've never seen this warning and I don't have any weather add-on's installed. Has anyone using the default weather seen this?

i have this warnings on longer flights most of the time, but as henry i also use ASE so maybe this is the problem.

[HenryD 39]

Just to clarify:

First of all English is not my mother language, so getting to explain physical issues is far off my "normal" English level. And so I think reading my first and especially my second post I understood the difference between these two temperatures very well. TAT may be exactly measured by a probe at the leading edges, but I tried to explain the physical effect that, because of the friction of the air surrounding the airframe, the temperature exactly near the airframe is in every case warmer than the SAT, how much degrees warmer is determined among other things by the velocity of the aircraft. So saying: "if I fly xxx hours at -53 it is no surprise that my fuel freezes to -47" is completely nonsense until you don't refer to which temperature. I know this is off-topic here now, but I don't like to get named as someone who does not know what he is writing.

Here you may read a short description of what I wanted to say :

Greetings

Consider TAT as aircraft Skin temperature, and if it is 0 then any water drop could/will freeze when in contact with the aircraft skin and ice will build up on the airframe

http://www.pprune.org/tech-log/413847-tat-vs-sat.html

Thus, an aircraft never flies in SAT, because his whole airframe is exposed to the friction of the air flowing around it while flying, "heating up" the airframe.

Back to topic, if no other will report this issue having no 3rd party weather installed, than it maybe related to a weather addon (like e.g. the S-turns flying PMDG aircraft with ActiveSky) and we will have to deal with it, unless Aerosoft and/or HifiSimulation will find a possible solution. At least PMDG and HifiSimulation (after some hesitation of both parts) get into contact and found a solution, that does not completely eliminate the problem but got it managed. I would like to see Aerosoft get in contact with HifiSimulation, because only the developers know how weather settings influence e.g. the fuel temperature (ok hopefully they should know). Therefore I understood dosdogru calling someone from Aerosoft for help.

Regards

Henry

[Paul_Smith 8]

That quote about TAT as skin temperature is only partially correct, and is only applicable to icing. The leading edges strike the air at the relative velocity of the aircraft causing the air to compress. This compression increases the effective temperature of the air and this is measured as TAT. This is very important for a number of reasons not least judging the risk of ice accretion.

However, and this seems to be what is causing confusion, the air passing over the rest of the skin is not compressed, so there is no heating effect. (There is a small friction effect but it is countered by thermal conductivity). This air will attempt to draw heat from the skin in exactly the same way that staic air of the same temperature would, which helps explain why it is called SAT. In turn, the skin will draw heat from its surroundings, including the leading edges and the fuel.

To sum up, consider TAT for icing every minute or so until you are a well outside icing risk, and consider SAT when doing fuel checks.

[Off-topic - Your english is excellent, I was not aware that it was not your first language. That said, I would rather be called some one who did not know then someone who did not learn].