Trouble at work with Her Maj in a flap (7)
I believe the answer is:
'a flap' is the definition.
(I've seen this before)
'trouble at work with her maj' is the wordplay.
'trouble' becomes 'ail' (synonyms).
'at work' becomes 'on' (on can mean activated or working).
'with' is a charade indicator (letters next to each other).
'her maj' becomes 'ER' (Elizabeth Regina ie Her Majesty Queen Elizabeth).
'on' after 'er' is 'eron'.
'in' acts as a link.
(Other definitions for aileron that I've seen before include "Plane control surface", "flight control", "Aeroplane's wing flap", "Hinged part of a plane's wing", "Aircraft control surface".)