They both mean the same thing :) With larger vehicles that are used for public transportation such as planes or trains, you can use "on" instead of "in". It gives the sense that you are using that vehicle to reach a destination. Some examples are I am on a plane (to Brazil). I am on a bus (to New Jersey). I am on a train (to Hong Kong). I am on a boat (to England). You cannot use this construction for smaller vehicles like taxis. You cannot say "I am on a taxi". I hope this helped :)

Both are correct. Few examples to help you understand better - 1) There were a hundred people stuck in the plane for 2 hours at JFK. 2) I saw my friend on TV. She was in a plane. 3) I'm on a plane. I'll call you as soon as I land.