You can check VAS (space left). Only with registered FSUIPC.
1-Open the FSUIPC setup screen. Go to the “logging” tab, and in one of the “specific value checks” enter the value 024C (first character is zero,
not the letter”O”.
2-Change the “type” for that value from S8 to S32.
3-Click on the checkboxes to display the value either at the upper window bar, or within the main FSX screen.
Now save and exit. Going forward, you will have a continuously-updated readout in-game of free VAS remaining.