The update manual (which comes with the Beta) clearly explains all of that, even making an example with the PMDG 777.
The PMDG Intro guide for all their airplanes states that fueling needs to be done via the PMDG interface, not external ones.
Which is why, the GSX Refuel system can be configured to NOT touch the airplane fuel system, and can be made to work in "Passive" mode, so it will just be an animation, but driven BY the airplane itself.
The PMDG is still refueling the plane, GSX will just react to this with its own animations, but it won't dare to touch the fuel on board.
The setting that controls this, is the "Show Fuel and Cargo" option in the GSX airplane configuration
- If it's UNCHECKED, the plane will be left in control of the fuel system, with GSX reacting to it
- If it's CHECKED, GSX will take control of the fuel, adding a progressive refueling simulation to any airplane.
