Fans of the film often speculate why the characters didn't just fly on the giant eagles into Mordor and drop the ring into Mount Doom. This is not, in fact, a plot hole. This was explained in the book but the film makers didn't think there would have been a need to because they felt it was obvious why they didn't do this. The eye of Sauron would have been a major obstacle. Even professor Tolkien vetoed the abuse of eagles' intervention when presented an early project of a movie from his book.