Is a "Sully"-style water landing possible over the Atlantic or Pacific?

Last night on “Lost,” Locke asserted “in calm seas, with a good pilot, the fuel tanks are buoyant enough to keep us afloat until we can get in the life rafts” with regard to the chances of a successful water landing. Is this accurate information?

It would seem that the ability to “glide” a plane down from 30,000 feet would be physically impossible.