I believe the movie you refer to is "Captains of the Clouds". Coincidently I had a good friend of mine who was a former RCAF WWII pilot and instructor. His name was Don Vickers and sadly Don passed away a year ago this month. One time after viewing the movie I e-mailed Don to ask if he had ever seen the flick. He replied "seen it, I'm in it!". Don was an extra in the Wings Parade scene with Billy Bishop and also one of the actual Hudson Bomber pilots as seen in the last scenes of the movie. Don told me that the "pea soup" fog you see while the aircraft were taxing around was real and not studio produced. In fact the fog was so thick one of the pilots crashed into one of the hangers. Don collected a couple of souvenirs and he gave me a piece of the bombsight from the smashed Hudson. He and several others were given leave to appear in the movie.