How Does It Feel to Fly? (1988)

Figment needs Beth and Danny's help right away: King Dreary has banished him and all his friends from the kingdom, for being make-believe fliers. Beth and Danny hit upon the idea of identifying and making lists of real fliers and man-made fliers, and then persuading them to leave the kingdom also unless the King lets the imaginary fliers back in. In the process they learn that every flight, just like a story, has a beginning, middle, and end.