on the wing

prepositional phrase4

1. •
   While flying.

   • Next comes a supposition, that the bird sleeps on the wing, and that the great distance from land at which it is seen at close of day is thought to favour the supposition[…]. — 1835
2. •
   (figurative) In motion.
3. •
   (figurative) Departing.
4. •
   (figurative) During operation.