Revealing mistake: As the first chopper lands on the pad, you can see that the pilot is Cowboy, a clear reuse of the shot from the episode "Cowboy"
Visible crew/equipment: As The Bus nears Rainbow Bridge, there is a reflection of either the camera vehicle or equipment in the lower right side of the windshield.
Answer: The C-42 was a military variant of the Douglas DC-2. Very few C-42's were built, so it's questionable that Potter would specifically have seen that particular model, but, given his military background, it's not entirely unreasonable that he might use the military designation even when the aircraft in question is actually a civilian DC-2.
Tailkinker ★