That might be for weight and balance, but I'm not sure. Our OM shows burning the center tank down to 10K on the 100 and 720, but zero on the 300. Below a certain load in the mains (8k or so) then the 100s burn the center to zero, but no explanation is given

1 hour ago, avallillo said:

That might be for weight and balance, but I'm not sure. Our OM shows burning the center tank down to 10K on the 100 and 720, but zero on the 300. Below a certain load in the mains (8k or so) then the 100s burn the center to zero, but no explanation is given

That is very helpful. Thankyou for explaining :)

Very good!!! as usual with your vids !!!

4 hours ago, jcomm said:

Very good!!! as usual with your vids !!!

Thankyou for your kind words

13 hours ago, avallillo said:

That might be for weight and balance, but I'm not sure. Our OM shows burning the center tank down to 10K on the 100 and 720, but zero on the 300. Below a certain load in the mains (8k or so) then the 100s burn the center to zero, but no explanation is given

So for the -300, fuel management is somewhat similar to the 747? Burn centre to zero, feed from inboards 2&3 until 2=1+res and 3=4+res, then tank to engine? :)

Phase-by-Phase Fuel Burn Sequence

• Takeoff:

  • Each engine runs in a strict "tank-to-engine" configuration from its respective Main Tank (Main 1 to Engine 1, Main 2 to Engine 2, etc.).

  • The Center Wing Tank is isolated during takeoff to guarantee dedicated, uncompromised fuel pressure to each engine during maximum thrust.

• Climb and Early Cruise:

  • Once established in the climb, the Flight Engineer opens the crossfeed manifold.

  • The Center Wing Tank override pumps are turned on.

  • Because Center Tank pressure is higher than the Main Tank pumps, the Center Tank feeds all four engines simultaneously until it is completely empty.

• Mid-Cruise (Tank-to-Engine Transition):

  • When the Center Tank empties, the Flight Engineer closes the Center Tank pumps and returns the aircraft to a tank-to-engine configuration, burning fuel from Main Tanks 1, 2, 3, and 4.

• Late Cruise (Reserve Transfer):

  • Once Main Tanks 1 and 4 burn down to a specific structural threshold, the Flight Engineer manually opens transfer valves.

  • Fuel from the outboard Reserve Tanks gravity-drains into Main Tanks 1 and 4 to maintain wing-bending relief and feed the outboard engines.

• Final Flight Phase:

  • The aircraft finishes the flight feeding directly from the four Main Tanks until landing.

"Gemini dixit"

28 minutes ago, jcomm said:

Phase-by-Phase Fuel Burn Sequence

• Takeoff:

  • Each engine runs in a strict "tank-to-engine" configuration from its respective Main Tank (Main 1 to Engine 1, Main 2 to Engine 2, etc.).

  • The Center Wing Tank is isolated during takeoff to guarantee dedicated, uncompromised fuel pressure to each engine during maximum thrust.

• Climb and Early Cruise:

  • Once established in the climb, the Flight Engineer opens the crossfeed manifold.

  • The Center Wing Tank override pumps are turned on.

  • Because Center Tank pressure is higher than the Main Tank pumps, the Center Tank feeds all four engines simultaneously until it is completely empty.

• Mid-Cruise (Tank-to-Engine Transition):

  • When the Center Tank empties, the Flight Engineer closes the Center Tank pumps and returns the aircraft to a tank-to-engine configuration, burning fuel from Main Tanks 1, 2, 3, and 4.

• Late Cruise (Reserve Transfer):

  • Once Main Tanks 1 and 4 burn down to a specific structural threshold, the Flight Engineer manually opens transfer valves.

  • Fuel from the outboard Reserve Tanks gravity-drains into Main Tanks 1 and 4 to maintain wing-bending relief and feed the outboard engines.

• Final Flight Phase:

  • The aircraft finishes the flight feeding directly from the four Main Tanks until landing.

"Gemini dixit"

Interesting. Gemini seems to have done some homework :) Nice one. I sometimes like to test these AI's to see if they know their stuff 😅

According to the UAL B720 manual, even for tank to tank configuration, any one of the crossfeed valves can be set to open to keep the crossfeed manifold pressurised. Same for the B727 where the No. 2 crossfeed is generally kept open.