It needs a better title
I realize it's the guy's nickname, but the word "sully" brings to mind negative connotations. The dictionary defines "sully" as "damage the purity or integrity of; defile." From a marketing standpoint that title could be a tough sell or at least misrepresent the movie, particularly in other English-speaking nations where the story may not have been as big. Honestly if I did not know the story and saw only the title and the fact that it's about a pilot, it would bring to mind the Denzel Washington movie "Flight" from a few years back. Which was a good movie, but I'm not sure anybody would go see a retread of it this soon (I would if Clint were directing, but still...).
I'm not trying to poke fun at Captain Sullenberger so please don't take my comments as such. All I'm saying is that I'd be a bit concerned about the title if I were producing the movie. Apparently it's based on Sullenberger's book, which is entitled Highest Duty. That still doesn't strike me as a great title for a movie, but it is a good deal better.