fix(a380x/fuel system): A380X Fuel System Improvements

[donstim]

Fixes #[issue_no]

Summary of Changes

Fixes fuel transfer rates, which were much too high.

This change will probably also fix the issues reported by a few users, which were cause by unbalanced transfer rates into the different feed tanks. This was probably due to the large disparity between fuel flow per 1 psi parameters to get the fuel system junctions to work properly initially. Asobo improved the junctions, but these values still seemed to work fine and were carried over. However, some users are having issues, probably caused by a combination of the excessive flow rates and the large disparity between the fuel flow per 1 psi parameters in some of the fuel lines.

The fuel flow per 1 psi parameters have been refined to continue to provide the intended match of flow rates to each feed tank when different numbers of junctions exist in the lines between feed tanks (there is one more junction in the lines to feed tanks 2 and 3 compared to 1 and 4). The pump pressures were adjusted to provide the fuel transfer rates noted in the References section below.

Screenshots (if necessary)

References

From the A380 FCOM, fuel transfer rates are as follows:

• From the inner or mid tanks to the feed tanks: 10 T per hour per feed tank
• From the trim tank to the feed tanks: 5 T per hour per feed tank
• From the outer tanks to the feed tanks: 8 T per hour per outer tank

Due to limitations with the MSFS fuel system, the transfer rate in the A380X assumes all feed tanks are being filled simultaneously. This means that the transfer rate for the inner or mid tanks to the feed tanks is set to 40 T per hour (10 T per hour times 4 feed tanks), or 20 T per hour per inner or mid tank. The transfer rate for the trim tank is also set to 20 T per hour (5 T times 4 feed tanks).

Additional context

Known issue: Sometimes the indications shown on the lower ECAM page for fuel transfers can be incorrect. For example, when the sum of the mid tanks is less than 8 T, the begin transfer trigger shifts to a lower level for feed tanks 2 and 3. This is done correctly by the fuel system, but the ECAM FUEL page indication appears to show that fuel should be transferring beginning at the higher trigger point. It will look like fuel should be transferring into feed tanks 2 and 3 when it is not.

Discord username (if different from GitHub): donbikes

Testing instructions

1. Confirm (using the FUEL page on the lower ECAM) that all transfers still take place (no regressions). The transfer order is inner tanks, mid tanks, trim tanks, outer tanks, although a CG transfer can take place at anytime if the CG moves far enough aft. CG transfers will go from the trim tank to the inner tanks, or the mid tanks if the inners are empty, or the feed tanks if both the inners and mids are empty. The CG transfer will end after the CG is moved 1% further forward. All the other transfers are to the feed tanks. Would be good to have different loading states (all done through the EFB such that fuel loads with fuel in all tanks, no fuel in mid tanks, no fuel in inner tanks, no fuel in trim tanks, and no fuel in either inner or mid tanks are tested.
2. Verify that the transfer rates are as specified in the References section.
3. Verify that transfers do not cause significant imbalances between feed tanks (that is, the transfer rates to each tank are about the same).
4. Be aware that there are specific feed tank fuel levels at which the different transfers start and stop. I can provide further information on this if needed, or check the FCOM.
   NOTE: It is acceptable to just provide a link to the FDR file from your flight here, rather than monitor the FUEL ECAM page throughout the flight. I can get everything I need from the FDR file. I just need various flights at different fuel loadings, at least one of which needs to be a very long haul flight with a fuel load of at least 160 T.

How to download the PR for QA

Every new commit to this PR will cause new A32NX and A380X artifacts to be created, built, and uploaded.

1. Make sure you are signed in to GitHub
2. Click on the Checks tab on the PR
3. On the left side, find and click on the PR Build tab
4. Click on either flybywire-aircraft-a320-neo, flybywire-aircraft-a380-842 (4K) or flybywire-aircraft-a380-842 (8K) download link at the bottom of the page

[heclak]

Quality Assurance Developer Report

Discord Username : Heclak
Object of testing : #10407
Aircraft : A380X
Simulator : 2020
Tier of Testing : 2
Date : 30/11/2025

Testing Process:

Completed a full flight and monitored ECAM Fuel page for transfers. Performed a hold at cruise until outer fuel tanks are depleted. Initial fuel load was 77 tons. All fuel tanks with the exception of the mid tanks had fuel loaded.

Testing Results:
Passed

Transfers appear to performed as described. No fuel asymmetry observed. Unable to confirm fuel transfer rates but have attached FDR file for confirmation.

Negatives:

Conclusions:

Media:

FDR File: https://www.swisstransfer.com/d/5e748e16-ba8e-4768-945c-5bb4ea1b7c34