Banking controller one suffering at work? (7)
I believe the answer is:
aileron
'banking controller' is the definition.
(part of a plane controlling its tilting or banking)
'one suffering at work?' is the wordplay.
'one suffering' becomes 'ailer' (an ill or ailing person).
'at work?' becomes 'on' (on can mean activated or working).
'ailer'+'on'='AILERON'
(Other definitions for aileron that I've seen before include "Movable wing surface" , "Movable part of an aircraft's wing" , "Aircraft's wing foil that controls lateral motion" , "Movable part of an aircraft wing" , "Aeroplane's wing flap" .)