When John Sr. flies and lands at the airfield, he has four engines, two on each wing. When he hangs up his cockpit dome and props inside the hangar, he has only two engines. Also, when he goes to re-enlist, he has four engines, but when he goes to the race, he has only two.
When Johnny takes off after John uncovers him, John and Mary go to the door. John's tails colors mysteriously switch.