(A minor suggestion, but one that may help the effect your are wanting)
Rather than introducing a 'mysterious' fog, you can just use a normal one, or have the plane lose its way in cloud as it's flying through the mountains. You'll get all the 'lost after a plane crash' effects - but the players will still think they are in a "normal" game. This should help increase the impact of any 'weird' things that start happening.
(This is a trick from story and movie writing - take some time to make sure the characters are well established in their 'normal' world before throwing them into the 'special' world of the adventure - it makes the transition, and subsequent time in the 'special' world much more dramatic.)
EDIT: Thinking about this a little more, you could give them a normal (WW2) fire-fight or two after the crash before you start hitting them with the 'weird' stuff - they'll know somethings gone wrong (they're a bit beat-up, in the wrong place, with no maps, and no way to call for help) but won't know how badly wrong for a while.
Lots of potential for suspense, shock and awe there.
