Originally Posted by Tex37
Probably been covered before, but so far as I am aware, the fuel pumps on commercial aircraft (not x feed) are gravity-fed pumps as the aircraft is not expected to fly inverted or in any aerobatic attitude, also as a result, the outflow from the wing tanks is at the lower point.
Yes, it has indeed been covered on this thread. And in quite some detail, complete with drawings. And yes, fuel is drawn from the tank low point (duh!), but no, gravity-feed or suction-feed is not the normal mode of operation, but an emergency.
Please see posts
#284,
#461,
#467 and
#478 for details.
Not knowing the full specs of the pumps on the 777 would they be able to draw such a vacuum as to result in physical distortion to the wing tanks, given the stresses they are designed to cope with in normal flight?
To the tanks, which really
are the wings, perhaps. Tank buckling would also have been noticed by the investigators. Also see below.
Give the fact that thrust was commanded on both engines at the same time with a slight imbalance of fuel in each wing tank, if vents were iced then the problem would replicate in each engine at more or less the same time.
Icing is a known problem, expected and well-understood by the designers of the venting system, and will have been taken into account. But even in the very unlikely event of complete blockage of the venting system, the boost pumps would still be capable of supplying enough fuel for quite some time. Given the large empty volume in the tanks, the under-pressure would only build very slowly.
Bernd