Tat

[jtr]

I think I get the point you are making John, however the joys of long haul are such that in my last trip, I did not see the sun for the entirety of two sectors (about 24 hours airborne, give or take).

So if this is the radiant energy you are speaking of, then I see little of it.

CJ, many thanks for your detailed explanation, however, my question (yes it is a broad one) still goes unanswered.

Is there any likelihood of the fuel temp getting significantly lower than the TAT.

By way of example, I have seen temperatures in the order of
-70 SAT,
fuel temp -41.
-40 TAT

Now my concern is that with an engine shut down (744), and the flight continuing to dest, the only heat source for 50 odd tonnes of fuel is the fuel/oil heat exchanger for the operating engine. So with all that heat sink, and cold temps, surely the fuel temp could become an issue.
To give some parameters to the query, I am refering to long haul scenarios, e.g. 10+ hours in the cruise. Getting airborne with 160t or so of FOB, you can find yourself 5 or 6 hours later, with 100t of the stuff, now 60deg colder than when you left! (these are extreme, but real numbers)
Interestingly, and this may be merely a reflection of the FCOM's we are given, the A340/330 had an IDG/fuel heat exchanger that had a return to the tank (well I think it did) however the -400 has no tank heating methods that I am aware of. There is a fuel/oil heat exchanger, but it seems to be an intergral part of the engine fuel pumping system. I have a sneaking suspicion that the HYD demand pumps have a fuel cooler of some form, but cannot recollect anything about the eng HYD pumps. QAVION, you awake?