How to repair Microsoft Flight Simulator on Steam

VERIFY INTEGRITY OF GAME FILES 

1. Launch Steam
2. From the Library section, right-click on Microsoft Flight Simulator and select Properties
3. Select the Local files tab then click the Verify integrity of game files... button.

4. Steam will scan the installation folder (C:\Program Files (x86)\Steam\steamapps\common\MicrosoftFlightSimulator) and download missing files or remove outdated or corrupted files - this process may take several minutes. 

WARNING:

By default, the launcher and the Core Content Packages (1.2 Gib) are installed at the following location:

C:\Program Files (x86)\Steam\steamapps\common\MicrosoftFlightSimulator

The Official and Community packages (i.e . non-mandatory packages) are later installed by default at this location:

C:\Users\Username\AppData\Roaming\Microsoft Flight Simulator\Packages\Official\Steam

If you have installed the non-mandatory packages with the Core Content Packages, the Official and Community Packages will be wiped out and you will need to re-download the Packages the next time you launch Microsoft Flight Simulator.