Looking for a fantasy anime movie
You're most likely thinking of the Windaria movie, based on a novel of the same name, by Keisuke Fujikawa. 

In the movie, when people die they turn into red light shaped like birds and fly to an airship in the sky over the ocean. 

It might also go by the name Legend of Fabulous Battle Windaria and Once Upon a Time, Windaria. The English version by Harmony Gold was rescripted and altered to include renamed characters, revised plot, and a happier ending among other things.