Although I have never seen this movie I can confirm that the flying sequences were shot at Monrovia Airport near Pasadena. This airport closed in 1953, according to the website "Abandonned and little known airports", which details many airports in California and elsewhere which were used as movie locations. Interestingly very close to the airport was the site of the very first Macdonalds restaurant. There is now no sign whatsoever that there ever was an airport there, like many old airports in the LA area the unstoppable tide of housing and commercial development has erased all memory. Laurel and Hardy also filmed at the airport on occasion, and I have seen amateur colour footage of a Boeing 247 being used during the filming of a scene at Monrovia from an unknown "gangster" movie.