A Totem Warrior Barbarian can gain this at level 14:
While raging, you have a flying speed equal to your current walking speed. This benefit works only in short bursts; you fall if you end your turn in the air and nothing else is holding you aloft. (PHB p.50)
Does this imply that you can start flying as you are on air? As I understand it, since it works in short bursts, the RAI is that you can leap off the ground, fly around, and then land back. In other words, you don't grow wings, you just manage to magically fly fueled by your eagle spirits.
My barbarian player, however, argues that he doesn't need an initial foothold. If he throws himself or falls off a cliff, he can just fly right before landing and avoid taking damage. This sounds terribly wrong, it allows you to fall down from 20 miles high and just magically land.
Is there any written rule for flying whilst falling? If so, does the Barbarian flight apply to it, meaning there is no need for an initial foothold?
Our homebrew rule was to decrease the speed at which he is falling (e.g., if he fell 50ft and has 30 fly movement, he slows down and takes damage as if he fell only 20ft).