When Axel's biplane crashes into the pond, the stunt pilot's goggles are still correctly in place as the aircraft settles. In the closeup, Axel's goggles are suddenly askew on his face from the "impact".
Throughout the scene where Mary Beth is wing walking, she is standing up while the dummy that was her stand-in was kneeling. So from one scene to the next the figure was standing, kneeling, standing, etc.
After Ezra crashes trying to do the loop Waldo takes off in a plane to chase of the spectators. The pilot is wearing goggles. In the subsequent shots where Waldo buzzes the crowd he is not wearing goggles.
When Ezra and Waldo drive up to the farmhouse in Ezra's pick-up it is very obvious that the truck looks far too old for the 1920's time frame of the movie. In the late 1920's that truck would have been new or nearly new. Instead, it is obviously 40 or 50 years old (which is just about exactly the age it would have been when the movie was released in 1975).