Approach little troublemaker, getting wind up (6)
I believe the answer is:
'approach' is the definition.
(I've seen this before)
'little troublemaker getting wind up' is the wordplay.
'little troublemaker' becomes 'imp' (I've seen this in another clue).
'getting' is a charade indicator (letters next to each other).
'wind up' becomes 'end' (I've seen this in another clue).
(Other definitions for impend that I've seen before include "Become imminent" , "Threaten; approach" , "Be about to take place" , "Threaten - be about to happen" , "appearing to be imminent" .)