So go to the location ice base assault, if you don't have that yet fly towards the base, then reload and play the location of Ice Base Assault. Attempt to land inside the ice base. If you get shot down, quickly press "restart here" right after you've been hit. Then try again and land. It may take you many attempts but keep trying. Once you land inside, turn around facing towards outside. Then set a spawn location inside the base. Now you restart the game and go to the location inside the base and fly outside. The missiles won't shoot you down! At least they won't shoot me.
Theres actually a unlockable location that spawns you inside the actual base and prevents the sams from shooting you because they see you as an ally
I did it by using my F-16 to shoot the missiles before they hit me. I saved the real location afterward. Took me a few weeks to find the default one.