Fliers (6)
'fliers' is the definition.
(I know this)
This is all the clue.
(Other definitions for pilots that I've seen before include "They fly aircraft and guide ships into harbour" , "Flies" , "Shepherds" , "Airmen" , "They are licensed to fly aircraft" .)
(Other definitions for birds that I've seen before include "Gulls" , "Egg-laying vertebrates" , "Terns and tits, say" , "Feathered fliers" , "4th" .)