Question

how do numetic bones help in flight in birds

Answer 1

Birds don't just have pneumatic bones in the skull ,they have them throughout the skeleton
It is this fact makes the bird's skeleton light weight and delicate and helps in flight of birds

Answer 2

Birds have pneumatic bones which are hollow and have internal spaces filled with air and are connected to respiratory system and allow more oxygen to be absorbed from air into the blood and they are present throughout the skeleton so they make the skeleton light in weight and provide strength and thus help in flight.