Under what conditions is internet required to watch a rented/downloaded movie on iPhone/iPad? I've had some issues before when trying to watch a rented/downloaded movie on a plane when I have no internet connection. Get the message that internet is required to authorize.

Under what conditions is internet required to play a rented movie (already downloded)?

Note: I typically download to my mac then transfer the movie to the iPhone/iPad using iTunes then night before. Not sure if that makes a difference.

I've successfully watched some movies but have had issues with others. Seemed like if I followed Airline instructions to completely power down my device, then it will give me an error if I try to playback later.

I often start the movie just before the flight when I do have internet and then pause it. Not sure if that is helping or hurting. No, not past the 24 hr mark at any time. I use this technique with the thought that if I authorize it once, then it won't try to authorize later. Maybe the powering down forces a re-authorization?

Note: I absolutely can't believe that I have to ask this question.
You always need an internet connection to start the rental period in my experience. Only a few packets need to transfer from the device to the server - so you are not streaming the movie.

Think of it like a credit card authorization - without the central server "charging" the rental, the 24 hour playback window can't start properly.

Your experiment that some rentals play is interesting and hopefully someone has a deeper packet analysis to present, but the safe bet is to not rely on a rental if you don't have in-flight WiFi to start the rental period and authorize the movies you intend to have "activated for watching" during the flight.