OK so I enter the fuel quantity on the FMC and load the fuel. There is now 10,000lbs of fuel in the plane. However GSX continues to ask me to set the fuel in the plane.
Most likely, you missed this in the GSX Manual, Page 20, the paragraph named "Refueling the PMDG 737" in the Refueling chapter:
How to refuel the PMDG 737
• Start by selecting an initial Fuel Quantity, using the “FUEL” option in the “FS ACTIONS” menu on the FMC. This will set an initial Fuel Quantity to start with.
• Call the GSX Fuel Truck.
• Do not change the Fuel quantity until the GSX Truck will be in position
• After the GSX Truck it’s in position, go back to the FMC, and click the desired Fuel quantity
• If the new quantity you selected it’s greater than the quantity you had when you called the Truck, the airplane will refuel itself instantly.
GSX doesn't support Defueling, and will only detect an fuel Increase, also because, if you were running on APU, it would consume fuel as well, that's why it GSX only checks for Increases, not just variations, otherwise the APU consumption could be confused by your own variation.
