Hi,
My old copy of FCOM mentions problems with JP 4 or JET B with various FLs and Fuel temperatures.
"Fuel in the center tank is to be regarded as unusable if the wing fuel temperature exceeds the following values before engine start and if the given FL is exceeded before the center tank fuel has been used :
+30 degs C not above FL 350
+40 degs C not above FL 300
+49 degs C not above FL 250
Reason : At high altitude with high fuel temperature, the pressure delivered by the center tank pumps becomes lower that the pressure delivered by the wing tank pumps."
So I think the blanket 49 degs C limit is much simpler.
Edit: Is it because the vapour pressure at high temperature and low atmospheric pressure can lead to cavitation on the suck side of the fuel pump with a low fuel head height? Not a problem on the wing tank pumps - because we don't plan to run those tanks dry.
Last edited by rudderrudderrat; 8th May 2010 at 09:25.