Flight sergeant taking aircraft in — regularly — heads there (5)
I believe the answer is:
stair
'flight' is the definition.
(I've seen this before)
'sergeant taking aircraft in regularly heads there' is the wordplay.
'heads there' indicates taking the first letters (only the heads of the letters).
The initial letters of 'sergeant taking aircraft in regularly' is 'STAIR'.
(Other definitions for stair that I've seen before include "One of a flight of steps" , "this could get one down" , "Word linking way and well" , "Tread and riser" , "Set of steps" .)