Do you think that flight is the air bending sub element? I mean think about the other subelements...Water has bloodbending and healing (both are bending water in a different form than water bending normally is used) . Earth has metal and lava bending (both are forms of the earth but not just pure earth) . And fire has lightning (both are bending forms of energy). So I think that flight should be airbending's subelement because. Airbending is a spiritual bending style and was even restored during harmonic convergence because of its spiritual connection. And to be able to fly you need to be spiritually enlightened sort to speak so both air bending and flight are forms of spiritual bending, sort of.
Yes I'm pretty sure flight is the official air bending sub skill also combustion is a sub skill of fire along with spirit reading but air has flight spirit projection and anaphylactic shock as possible sub elements
Sorry but the above post in incorrect. Astral Projection is the sub skill for airbending. It was confirmed by the writers. As for Flight, is a an extremely rare speciality for air-benders (only 1 other air-bender has ever done it). It's most likely like combustion for fire-benders, Lava-bending for earth-benders, and psychic water bending for water-benders.
To scoutpower1: In my studies of martial arts chi has come into conversation many times and from ancient teaching bending was one a real art. Thought there is nothing to prove that it was. But in my learnings there is no such thing as soundbending. As of sound its self is not an element such as EARTH AIR WATER and FIRE