The number one rule in making a thriller is, if you're ripping off Hitchcock, make sure you do it right! The movie's plot is very simply Hitchcockian -- a woman, Jodie Foster, loses her little girl aboard an international flight several thousands of feet in the air, and nobody on board remembers seeing the little girl at all, much less her disappearance. The movie's full of simple plot elements: a desperate mother, the claustrophobic atmosphere of the plane and the helpless skepticism of the airline personnel. The problem is the plot ultimately makes no internal sense, and the underlying emotional issues, while beautifully played by the talented Ms. Foster, are idiotic as well. All movies like this are manipulative by nature, but the really good ones hide the strings (Hitchcock was a Master of this art) while the bad ones, like Flightplan, display their flaws so obviously you find yourself sitting in the theater snorting at the improbability of what's happening. The big twist that's supposed to shock doesn't make sense, supposedly intelligent characters act extremely stupidly and the emotional manipulation is ham-handed and ineffective.
So -- what did this movie do right? The performances are uniformly decent, though not in themselves interesting enough to save the movie. And the director keeps the movie from utter pointlessness by keeping the movie visually interesting. The movie's color palette is blue and grays, and the airplane is full of sleek curves and surfaces. The camera does all sorts of tricks, like filming a conversation from the outside of the windows, but which ultimately does nothing for the story or the movie overall.
I didn't hate this movie, mostly I was dismissive of it. Nothing engaged me, or interested me, and the ending made me roll my eyes. It's true: a bad script kills a film every time.