Continuity mistake: When Bosley is in the dungeon towards the end of the movie he is seen ripping his sheet to shreds trying to make a rope. If you look in the window where he throws his rope there is light coming in from outside - not necessarily daylight, but a floodlight or similar. From outside though, the wall is pitch black, with no light coming from the room either. (01:01:10)
Continuity mistake: In the last scene with the tugboat you can see the wake starting a few hundred meters behind the boat, even though it is supposed to have been sailing for a while.
Continuity mistake: In the car chase scene, when the red Ford Taurus flies into the air and flips, in one shot its a 96-97 model, in another shot it becomes a 98-99 model (grille is different).
Continuity mistake: In the fight with the thin man, after Natalie hits him Dylan already has her leg lifted to hit him but Alex doesn't. In the next shot they lift and hit at the same time. (00:25:20)
Suggested correction: Knox wasn't a trained pilot. Either he had no clue to what was going on, or he thought something may have been wrong, but didn't know what to do about it.
Taking off and landing a helicopter are by far the most intense and difficult part of a pilot's training. Seriously, 99% of learning to fly is learning how to land and take off. If the pilot is skilled enough to take off in a Huey he is easily skilled enough to notice a massive additional drag on his helicopter due to the additional weight of the angels and the air resistance put up by such a bulky protrusion on his aircraft. If he isn't skilled enough to notice that, he isn't skilled enough to take off in the first place.