investigating Inflight Fuel Management

[MD82]

Hello ini,

as I progress through my long-range flights, I'm having fuel balancing problems between tanks. The rule is that as the fuel quantities between Tank 1, Tank 3 and the SUM of Tanks 2L and 2R become equal, fuel configuration changes to the "tank-to-engine" config. In this configuration, Tank 1 feeds ENG 1, Tank 3 feeds ENG 3 and Tanks 2L+2R feed ENG 2 (Hence the need for the sum of the 2 tanks). With all cross-feeds now closed and all engines consuming fuel at the same rate, the ratio of equal amounts between tanks 1, 2L+2R and 3 should persist. 

Here is what I am observing:

As I manage to re-match the fuel quantities exactly, you can see I am about to return to the tank-to-engine configuration.

Re-configuring is now complete, with all pumps ON and all cross-feed valves closed. Fuel quantity of 30.3k Lbs equal in tanks 1, 2L+2R and 3.

To make sure, all three engines are consuming fuel at the same rate.

After 20 minutes in the tank-to-engine configuration tanks 1 and 3 are at 28.7 while tanks 2L+2R are at 31.5. A difference of 2800 pounds of fuel. How can that be, if all cross-feed valves are closed and all three engines are consuming the same amount of fuel?

Cheers,

777Drvr

[richboy2307]

Thank you for your detailed report. That imbalance does seem odd, the team will investigate further and we'll reach out here in case any additional information is required.

[fishermanivan]

5 hours ago, richboy2307 said:

Thank you for your detailed report. That imbalance does seem odd, the team will investigate further and we'll reach out here in case any additional information is required.

 I get the same thing, just FYI

[richboy2307]

Hi,

Thanks for your patience. Please see response from our dev team:

Quote

The correct procedure is to have the crossfeeds open for fuel quantities above 58k lbs on the -500 as the gravity is greater between center and outer wing tanks. The tank-to-eng config should only be used for quantities less than 63k lbs. 

We may not have this -500 specific difference captured in our manual, but should be simulated in the current fuel system implementation code-side.

We will update the manual accordingly, but if you notice any discrepancies even after following the above, please let us know.

Thanks!

[fishermanivan]

On 4/27/2026 at 5:18 AM, richboy2307 said:

Hi,

Thanks for your patience. Please see response from our dev team:

We will update the manual accordingly, but if you notice any discrepancies even after following the above, please let us know.

Thanks!

Not sure that helps my brain haha..  I'm still confused about when to go Tank to Engine.

[richboy2307]

Try this recommended procedure

If starting fuel quantity is less than 63,000 lbs:

• Feed tank-to-engine throughout flight.

If starting fuel quantity is between 63,000 lbs and 116,000 lbs:

• Crossfeed all engines from tank 2 until fuel levels in all tanks are equal. Leave one tank pump operating in tank 1 and tank 3 while crossfeeding from tank 2. Monitor tank quantities to ensure that lateral balance remains within limits.

•  Feed tank-to-engine for remainder of flight, especially when fuel remaining fuel quantity is less than 63,000 lbs.

If starting fuel quantity is 116,000 lbs or greater:

• Crossfeed all engines from tanks 1 and 3 until total fuel remaining is 116,000 lbs.

• Crossfeed from tank 2 until tanks 1, 2, and 3 are equal. Leave one tank pump operating in tank 1 and tank 3 while crossfeeding from tank 2. Monitor tank quantities to ensure that lateral balance remains within limits.

•  Feed tank-to-engine for remainder of flight, especially when fuel remaining fuel quantity is less than 63,000 lbs.