I see page 31:
Air units that are overrun lose 50% of their strength and go on the deployment queue of the enemy.
But I see page 67:
Enemy air units overrun by land units lose strength according to their current effectiveness and go to the deployment queue to be redeployed next turn.
And page 68:
Overrun — Land units may overrun enemy fleets and air units. Fleets retreat to sea and air forces are placed on the deployment queue taking damage according to their effectiveness.
Obviously, this is the next turn but when do they come back? [:D]