If it's the story I'm thinking of, it's (very loosely) based upon actual wartime events at Colditz castle.
Some other movies and/or made for TV shows:
COLDITZ - starring Jason Priestly (there's a short advert, followed by the trailer) Here's a
YAHOO link. (interestingly, one film is titled 'Colditz' while the other is titled 'Escape from Colditz', but both appear to have the same cover photography)
The Colditz Story - this is a review of an older film
But, after looking, Otto's suggestion of
The Birdmen appears to be on the mark for the film you're looking for.
As I mentioned earlier, all of these films are based upon an actual escape attempt from the very real
Colditz Castle - however, the glider construction effort was underway but never completed at the time of liberation.
If you'd like to tour the castle, and also visit Arnhem ('A Bridge Too Far') as well as visit some 'Dambusters' sites (including the dams and the gravesite of Guy Gibson, V.C.), then check
THIS out!
Welcome to the forums!
-whatever
-Lou