In one of the final "after capture" scenes, as the plane bringing him home in handcuffs from France approaches New York, Frank remarks to his captor that he remembers "runway 44 at La Guardia". No runway at any airport in the world has the number 44; runway numbers are the compass heading in ten-degree increments, with 01 being 10 degrees east of due north, 09 due east, through 36 for due north. And all runways have dual designations differing by 18 for the two possible takeoff/landing directions.

If Frank had faked being a pilot for a couple of years, EVEN if he only rode jump seat and never actually tried to fly the plane, he would have noticed how runways are designated.