Meiklour: I have already gone through QRH before posting my observations. The excerpts of the QRH given under 'GRAVITY FUEL FEEDING'are given below.
If no fuel leak and for aircraft handling:
If no fuel leak, and for flight with only one engine running (this engine being fed by gravity), apply the
following:
FUEL X FEED........................................................ ............................................ON
BANK ANGLE...................................... 1 ° WING DOWN ON LIVE ENGINE SIDE
RUDDER TRIM........................................................ ........................................ USE
As you may know, gravity fuel feeding is required when you experience FUEL 1+2 LO
PR.
Now, literally reading between the lines from the above checklist...'flight with only one engine running (this engine being fed by gravity)'
INFERENCE: LIVE ENGINE -- DEAD FUEL PUMPS(fuel pumps are dead on the same side as the live engine)
My understanding:
CASE1)The above procedure is assuming that the live engine is fed by gravity from the onside wingtank due to fuel 1+2 LO
PR on the onside wingtank and for aircraft handling, the x-feed is opened to use the fuel from the other wing tank whose wing tank pumps are perfectly alright.
Hence, my previous observation about the usable fuel in post #18.
CASE2) This checklist is meant for a highly improbable scenario of having fuel L TNK 1+2 LO
PR combined with fuel R TNK 1+2 LO
PR(CENTER TANK EMPTY) snags and then opening the x-feed for reasons mentioned above. In that case, my post #18 would be in error..