Hello, everybody

I have recently watched the Non-Stop movie with Liam Neeson, and found it very unrealistic.

So, I would like to ask a few questions.

What rights and powers do real air marshals have?

Do they have rights to search, detain, or interrogate anybody onboard?

Do they comply completely with captain's orders?

What would they actually do in reality, if some movie-like problem would occur and the suspect on board would require to be identified and found first, before he could just be neutralized and apprehended?

As I know, it never happened in reality, did it?

Would they search passengers on board if landing is impracticable and the threat is believed to be in one's carry-on or under one's clothes?

Thank you!