Most air services provide these flights (6)
I believe the answer is:
stairs
'these flights' is the definition.
(I've seen this in another clue)
'most air services provide' is the wordplay.
'provide' indicates a hidden word.
'STAIRS' can be found hidden inside 'most air services'.
(Other definitions for stairs that I've seen before include "A set of rising steps" , "Interior means of ascent" , "4 and 8 (to the cockney)" , "Ascending flight of steps" , "Way between floors" .)