Visible crew/equipment: When Klinger's in Colonel Potter's office wearing the fur coat and rubber reducing suit, just as Potter says, "This one is definitely in the running," we can see the shadow of the boom mic shaking up and down on the wall, at the left side of the screen.
Visible crew/equipment: As Klinger sits in the chair dressed in a winter coat, you can see the boom mic and light panel reflected in his shades.






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 ★