I have been having this issue since the beta version but waited for the official version to see whether it would be fixed or not
Then you SHOULD have reported it while we were in Beta! What's the point of having a Public Beta, if not for getting feedback ?
I suspect it has something to do with the APU consuming fuel that resets the procedure, since i tried refueling with APU off and everything went well. Still a bug though
With the Airbus doing the progressive refueling, GSX doesn't touch anything in the fuel. BOTH the refueling progress and the eventual fuel consumption are entirely controlled by the airplane itself.
Now, in order to decide if the refueling should stop, GSX checks if there's a continuos POSITIVE change in the fuel quantity. Now, in order for the APU to have an effect on this, it would be necessary the APU consumption being HIGHER than the refueling speed of the airplane.
And yes, we noticed the Aerosoft Airbus progressive refuel seems to be much slower than the GSX one (when GSX controls a default plane), and since the GSX refueling speed is realistic accordingly to real-world specifications, the first issue might be the refueling speed of the Aerosoft Airbus is too low.
An additional issue, might be the APU consumption being too high so, the combination of the two, result in a negative value if the APU is running.
Just to give you an example, a normal APU consumption is rated in lbs per HOUR, while a realistic fuel truck pump can pump at a rate of hundreds of gallons per MINUTE!
A third possible issue, is that I believe the Aerosoft Airbus DO NOT support the simulator Time Acceleration when doing its own progressive refueling (not 100% sure about this, but I think I have noticed it while testing) simulation. Which means, if the APU supports the sim's Time Acceleration (so, it's burning fuel several times faster than realtime), but the progressive refueling doesn't, and you used the Time Acceleration for a while, this could explain how the APU could be able to burn more fuel than what is being pumped.
So, it's possible the "bug", it's really a combination of all these problems.
The GSX fuel truck, when it's in command of the plane and it's doing the progressive refueling on its own, properly supports BOTH the sim Time Acceleration, and its own Time acceleration (the combine so, if you have 4x on the sim and 5x on GSX, it will refuel 20 times faster), so it cannot be fooled by the APU fuel consumption, assuming the plane is using the default APU sub-system.
