Just a head's up/FYI--not a complaint. This may or may not be related to the trainer. I was using infinite ammo/health options when this occurred. Started mission 13 which forces you to use a beacon instead of your normal special weapon. After the briefing and plane selection, when the game starts to load the mission, it crashes and displays a "fatal error" message. Attempted to restart the game without the trainer but still get the crash, so my save appears to be broken. Just sharing this in case it is related to using the trainer. You may want to exit the trainer prior to mission 13.
Have you already verified the game files in Steam?