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T777 Low Fuel temperature

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Hi

 

I was enacting QFA7557 from PANC to KORD

 

One hour into the flight at FLT370 "Low fuel temperature" sign popped up.

 

Checklist idicates to increase speed or descend to a lower altitude.

 

Increasng speed did not do it. I descended to FLT330 and that did not do it.

 

The sign stayed on until landing at KORD 6 hours later.

 

Is there another solution to this. and how low temperature may affect the flight/Aircraft? Just curious

 

 

Thanks

 

Bill

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Hi Bill,

 

if you have Foreflight on an Ipad you can tap the airport nearest to you, select winds aloft, then view the temp for the altitude nearest you. Another option is to go to the environment Canada weather site for aviation weather if you were over Canada when the  warning occurred.  I am assuming you were using a weather program that provides real world weather.  There may not have been hardly any temp difference between 370 & 330.

 

Dave

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Is there another solution to this.

 

No other solution afaik.

Bare in mind that the warning comes on before reaching the actual Fuel Freezing temperature, which differs depending on fuel type (nominal -40 for JET A; -47 for JETA1).

In your case departing from PANC you can assume to have carried JET A, therefore if fuel temperature got close to -40, I would have seriously considered descending more and/or divert, if the temperature cannot be controlled.

 

 

 


how low temperature may affect the flight/Aircraft?

Possibly engine/s flameout, serious matter.

 

Very interesting and realistic scenario, usually likely to happen on ultra long haul flights.

 

 

 


What can low fuel temperatures do to a 777?

 

That was more of a low water (in tanks) temperature if anything :-)

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greggerm, on 23 Jan 2017 - 08:44 AM, said:

What can low fuel temperatures do to a 777?
 
That was more of a low water (in tanks) temperature if anything :-)
Correct. The same thing would have happened if the fuel reach -20 or -40 degrees - the water was excessive, froze, then turned to slush as it warmed up and clogged the engine intake. (NB - simplified version)

 

In reality, the fuel will start to gel-ify and small particles of wax will start to form. This is when you have problems..

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Question still remains...Will it affect the flight, as in, is freezing fuel actually modeled in FSX / PMDG T7?

 

I had a similar message pop up while enroute from WSSS to EGLL. SAT, if I remember correctly, was -61C (cannot remember TAT) Tried both the speed increase and a lower FL but neither did any good. Climbed back to FL380 and eventually the warning disappeared. Checking my fp at that particular waypoint the expected SAT had climbed to -54C.

 

I would like to know whether this is modeled with the T7 or if it is a Failures option that when enabled will cause issues for the actual flight.

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Increasng speed did not do it. I descended to FLT330 and that did not do it.

had this the other night had to descend to fl below 300 think it went away around 280

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Will it affect the flight, as in, is freezing fuel actually modeled in FSX / PMDG T7?
I tried when the 77L was released to make it freeze and had it as low as -47ish I believe, and nothing happened. It would be difficult to accurately simulate as I doubt there is much data out there as to what happens. I think as long as it is able to enter the pumps and flow, even if quite viscous,  you would not get a full flameout as the fuel-oil heat exchanger will warm up the fuel heading for the engine itself. Probably more a power roll-back due to the decreased flow rates. I do recall the one wing will usually be slightly warmer than the other as there is another heat exchanged that uses this wing as a heatsink. I can't recall which one. The system typically takes it temp reading from a worst-case location, so, the area most likely to be the coldest. (I believe - may be wrong on that one)

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I did a test - loaded some fuel with the outside temp set to -55degC (lowest P3D will go) and managed to start both the APU and engines, and bring them to full power:

 

2017-1-23_18-14-55-960_zpsgrmvi0mu.png

2017-1-23_18-17-32-107_zpsfxspjglb.png

 

So I think that settles it...

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Is there any possibility to tell the 777 what kind of fuel (Jet A vs Jet A1) is in the tanks, or does the warning come up assuming Jet A (-40°C) regardless of the actual fuel type?

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Thank you all for your amazing input. I love the PMDG 777.

 

Yes I did use ASN with stormy winter theme. What troubled me is when I go to KORD and descended to 12000 the warning did not go off. And no other failures or warnings occurred.

 

 

Bill

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What troubled me is when I go to KORD and descended to 12000 the warning did not go off

 

What was the fuel temperature at that time? Bear in mind it takes time for the cold-soaked fuel to warm up.

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Here's a little bit of insider knowledge for you. Seemingly they won't you dispatch you into areas where there will be a problem. 

 

 

secret.png

  • Upvote 1

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Interesting factoid I read once, the coldest air is generally found over the equator, because the atmosphere bulges out at the equator and the thermocline (point where temperature stops decreasing, transition to stratosphere) is higher allowing a greater temperature decrease.  Since most flights only transit the equator and not fly parallel to it this is seldom a problem.

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Since most flights only transit the equator and not fly parallel to it this is seldom a problem.

Dan

I flew the equator from Singapore eastbound to Singapore. Took 48 hours. I wanted to see if the T7 and FSX would last that long without puking. The flight was between FL330 and FL370. I had no problem with Low Fuel Temperature. But that was in the simulator not the real world. I believe the weather engine was ASN. Obviously I had to keep adding fuel through the FS Actions Menu.

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