Funniest one I remember was an unknown WW2 hero film, supposedly deadly serious, where the two pilots (one of whom was possibly John Wayne) were flying a tandem Navy dive bomber. They were on a mission "flying in cloud somewhere over the Pacific Ocean", when the outline / shadow of a man suddenly appeared and slowly went past the cockpit.
Also the film "Airport" when ATC were talking down a 707 in a thick snowstorm to the dramatic sounds of an orchestra. The pilot was struggling to keep the aircraft upright, but the controller was so very helpful, saying useful things like "A little more left rudder, Jim".
Perhaps we should have another thread on the best "aviation film howlers".