Taking flight running fast (6)
I believe the answer is:
flying
This clue is a double definition.
'taking flight' is the first definition.
('fly' can be a synonym of 'take flight')
'running fast' is the second definition.
(I've seen this before)
(Other definitions for flying that I've seen before include "(Of time) passing swiftly" , "shooting" , "(Of flag) displayed on a flagpole" , "Getting high" , "In the air; very brief (visit)" .)