Recently in 1.9 Pre-Release 1, a change was made to Elytra in which entities wearing them while in midair must use the jump input to activate gliding. It works properly for players, but a presumably unintended consequence of the change is that any other entity besides the player cannot use Elytra to glide since the entities don't know how to activate the jump input. This mechanic was greatly appreciated as it allowed for both fun in creative mode (we had real flying pigs!) and amazing mapmaking opportunities like raycasting. I would hate to see this mechanic go, so please revisit this before 1.9's full release! I would assume that the solution is to use the old gliding activation code for every entity but the player and use the new code for no other entity but the player.