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keight

Fuel temp pred

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hello

got a caution message "Fuel temp pred". qrh says: fuel temperature is predicted ti be low after reserve transfer occurs.

but the message remains there although transfer has already been occurred and fuel temp (-27) is higher than entered in FMC -37.

is it normal behavior?

if0P5.jpg

thanks

Edited by keight

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It gets a little complex as it depends on the type of jet fuel being used (which I don’t think is selectable in the sim). The freezing point for standard Jet A is -40, and fuel temp must be kept at least 3 degrees higher than freeze point. So unless your fuel temp is approaching -37 you are within limitations. Seems a little odd that the message came up but it could be due to the low TAT. 

Edited by Jetlinker

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The reserves are located outboard in the wing and the fuel there can become much colder than the fuel in the mains, and the logic is just telling you that under these conditions you need to keep an eye on fuel temps.  This is an advisory message. 

Fuel freezing point temperature is entered on the PERF INIT page, and is -37C if none is entered.  FCOM 12.20.1

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thanks gents, but the question was is it normal that the message stays there after the condition has gone (transfer occurred and fuel temp is higher than temp entered in FMC)

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Good question.  I recommend you ask that of PMDG on a trouble ticket.  Did the message persist until the end of the session or did it clear when the TAT increased from -39C?  I suspect the message will remain as long as the TAT is below the freezing point of the fuel for it is a sure thing that the fuel will cool to the TAT given long enough.  As mentioned, it is an advisory and you can cancel it but if or when you get the FUEL TEMP LOW warning you will have to do something.

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46 minutes ago, downscc said:

Good question.  I recommend you ask that of PMDG on a trouble ticket.  Did the message persist until the end of the session or did it clear when the TAT increased from -39C?  I suspect the message will remain as long as the TAT is below the freezing point of the fuel for it is a sure thing that the fuel will cool to the TAT given long enough.  As mentioned, it is an advisory and you can cancel it but if or when you get the FUEL TEMP LOW warning you will have to do something.

You can clear the message from the display, but you cannot cancel it if the predicted conditons still exist, so the message will re-appear whenever you hit the Recall button.  Looking at the screen capture I can see that the SAT is -68C with a Fuel Temp of -27C. so in these conditions what you are seeing is perfectly normal because the sensors are comparing the Fuel temperature with the actual (enroute) outside air temperature; just as the non-normal checklist states.  Unless the OAT warms up significantly or you fly faster and/or descend into warmer air then under these conditions the fuel temperature will get much colder and the fuel will eventually start to wax and then freeze. 

Edited by berts
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