This quote from Flown-It at post 5871 five pages back, at 18th Mar 2014, 21:50
Lots been said about total electrical failure.
The Rollers on my plane are certified to my 51,000 ceiling BUT RR only guarantees them to suction feed to 20,000.
So what ceiling will the Rollers suction to on the T7? If closer to my 20K then MH370 could never have flown for the 7 plus hours. Thus total electrical failure seems unlikely.
Answers from T7 drivers please.
My buddy flies the 2ER and emailed me the fuel management system manual; I'll try to wade through it and figure it out for you. Just in general: the system is set up with (roughly) 26,000 gal in the center tank and 9,300 gal in each wing tank. Center has two fuel pumps, one for each engine, and each feed line tees into the line from the wing tank on that side. The center pumps are at a higher output pressure than the wing pumps, so with both center and wing pumps working all feed is from the center tank. If center pump is shut off and wing either fails or is shut off, then suction, but only from the wing tank apparently (at least, as far as I have deciphered). The entrained air in the fuel has been known to restrict power output and cause reverse flows through the compressor when the pump(s) are off, until all the air in the fuel is gone, so the drill is to run with all the pumps churning away, at least until center is reduced or empty.
From that I draw that after the fuel gets cold and the entrained air is finally gone, it should siphon just fine. At that point, likely not altitude dependent (although that is my surmise, and not from the manual).