Значение идиомы on the fly

[on the fly ] {adv. phr.} 1. While in the air; in flight.

Thebird caught a bug on the fly.

Joe was called out because thecatcher caught the ball on the fly.

2. {informal} Between otheractivities; while busy with many things.

The president was so busythat he had to dictate letters on the fly.

John is very busy, andpeople who want to talk to him have to catch him on the fly.

Compare:ON THE GO, ON THE WING.