Pilot-X (1936) [colourised]

Aviation whodunnit.
Passenger flights are being shot down by a mysterious bi-plane with an 'X' on the wing. The chief suspects are gathered together in an old mansion to try to find out who is responsible.

This movie is known by a few names, one of which was 'Death in the Air' in the USA and 'The Mysterious Bombardier' in the UK - and relies heavily on stock footage from air shows for the action sequences.

Starring: (source: Wikipedia)
Lona Andre as Helen Gage
John Carroll as Jerry Blackwood
Leon Ames as Carl Goering
Henry Hall as Henry Goering
Hans Joby as Lt. Baron von Guttard (Credited as John S. Peters)
Gaston Glass as Lt. Rene La Rue
Pat Somerset as Capt. Roland Saunders
Wheeler Oakman as Lt. Douglas Thompson
Reed Howes as Lt. John Ives
Willard Kent as Inspector Gallagher
John Elliott as Dr. Norris

Directed by Elmer Clifton