be on the wing
if a bird is on the wing, it is flying

[TahlilGaran] Dictionary of Contemporary English ▲

on the wing
in motion.
He started to run, but a rifle shot caught him on the wing.

Usage notes: based on the literal meaning of on the wing - flying:
The sight of so many enormous birds on the wing filled me with awe.

[TahlilGaran] English Idioms Dictionary ▲

on the wing
adv. or adj. phr.
1. In the air; while flying.
The duck flew away, but John shot it on the wing.
2. informal In constant motion; always very busy.
Susan was on the wing doing things to get ready for her trip.
Mr. Jones had a busy schedule and his secretary had to catch him on the wing to sign the letters.
Synonym: ON THE FLY.
3. informal Moving from one place to another; traveling; going somewhere.
Mary's husband is a traveling salesman and he's always on the wing.
They stayed in France for a week and then they were on the wing again.
Synonym: ON THE GO, ON THE MOVE.

[TahlilGaran] English Idioms Dictionary ▲