43 minutes into the film, Bonnie is eating breakfast. Her knife and fork change positions several times while talking with Geoff. Sometimes they are on the table, sometimes she's holding both and sometimes just the fork.
In the immediate aftermath of Joe's crash, distant shots show Bonnie with her left arm cocked at a right angle, but close shots show it limp at her side.
Before Kid's injury, the blood and wounds to his face keep changing.
When Joe's plane clips the tree and loses the right wing, the plane rolls to the left. In fact, asymmetric lift would roll the aircraft to the right due to greater remaining airfoil surface on the left side.
When the trimotor has two engines on fire, the radio at the station says, "Number four, left outboard, is on fire." The bird is a Ford Trimotor, only three engines.
When the TriMotor is returning, the lookout says that number 4 is on fire, and one might think that he is referring to engine number 4 (on a plane with only three engines). He is in fact talking about Plane Number 4.
When Carter is shot by Jean Arthur's character, the hammer on the the revolver had not been drawn back. It is thought that a revolver will not discharge from just being dropped on table unless it had been cocked; and even then it's not a certainty. However, an impact to the hammer commonly will discharge a round unless the cylinder behind the hammer is empty; that is how it is safely carried. (In modern revolvers, the transfer bar safety mechanism prevents this.)
Toward the beginning of the movie, when Tex the lookout radio man says, "OK, it's open," you can see the whole mountain range in the background slightly shift to the right. (Apparently, somebody was moving the set backdrop or bumped into it while the scene was being filmed.)
When McPherson takes off with the patient, the chimney smoke shows he's taking off with the wind instead of against the wind. Taking off against the wind would increase his relative speed and help him take off.
When Cary Grant enters his room and unknown to him, Jean Arthur is taking a bath, there is a coffee pot brewing on the hot wood-burning stove. Arthur places the pot on the table. The steam coming from the hot pot is not real Steam rises. To simulate hot steam, it appears to be dry ice in the pot as the vapor falls to the table and an over-abundance of it.
A 10,000 ton freighter pulls up to a rowboat dock to take on and discharge passengers.
After Geoff Carter is shot, Kid Dabb says he's better than anyone else around here while looking at Bat McPherson. However, Gent Shelton, although fired earlier, is shown several times in the bar, and therefore could be available to make the ill-fated flight.
When Geoff is accidentally shot, in the excitement of the moment, various characters refer to "Papa" and "Kid" interchangeably.