Fliers flapping arms (6)
I believe the answer is:
rifles
'arms' is the definition.
(rifle is a kind of arm)
'fliers flapping' is the wordplay.
'flapping' indicates an anagram (flap can mean to move or fly around).
'fliers' anagrammed gives 'RIFLES'.
(Other definitions for rifles that I've seen before include "Searches and robs, using longbarreled gun?" , "Shoulder firearms" , "Weapons; searches through" .)