To release a bird, kite, or balloon into the air to let it fly.
to permit takeoff
To permit an airplane or aircraft to take off, typically by a control tower.
to let go
To unleash or give free rein to (one's dreams, personality, etc.), often used in the phrase 放飞自我fàngfēizìwǒ (to let oneself go or be oneself without inhibition)