They fly around stormy Polar Sea, bearing north-east (10)
I believe the answer is:
aeroplanes
'they fly around' is the definition.
'stormy polar sea bearing north-east' is the wordplay.
'stormy' indicates an anagram.
'bearing' means one lot of letters goes inside another.
'north east' becomes 'ne'.
'polar'+'sea'='polarsea'
'polarsea' with letters rearranged gives 'aeroplas'.
'aeroplas' placed around 'ne' is 'AEROPLANES'.
(Other definitions for aeroplanes that I've seen before include "Fliers" , "Aircraft" .)