Hi NC,
You're just about there. Quite simply, all you need to do is animate the part as you're doing, frame 0 have it buried hidden in the wing. Then on frame 99 still have it hidden in the same position as frame 0, then frame 100 place it in it's exposed location required. It will not animate until frame 99 and must be fully finished animating by frame 100, so as it has only 1 frame in which to position itself, it seems like it instantly appears. If you're using Gmax there may be a way to instantly appear an object?
You can still use the wing fold ani, just animate as above. You can do this at any frame number just hide until the previous frame to the fully deployed frame number, so for example frames 0 and 66 hidden then exposed on 67 and 100. You must animate frame 0 and 100 (as in FSDS, but I suspect the same applies to Gmax).
Cheers
Shessi