Audio problem: At the end when Borelli is getting ready to take off, in the close ups you can see the main rotor blades starting to turn, getting ready to fly. But the sound suggests that the rotors and engine are already at full power.
Audio problem: As Hawkeye and Trapper get into the chopper, you hear the engine powering up, and the blades slicing the air, but the blades aren't moving at all.
Answer: Even an Army field hospital would have SOME weapons for self-defense if the enemy attacked. What's meant is that it's not a combat outfit, and therefore wouldn't have enough weapons to actually attack anyone. (It's also mentioned a few times that the Officer of the Watch is supposed to carry a pistol at all times, but Hawkeye refuses to do it when he's in charge and Colonels Blake and Potter don't enforce the rule).
Captain Defenestrator