Endless complaint — one couldn’t get off the ground (3)
I believe the answer is:
moa
'one couldn't get off the ground' is the definition.
(extinct flightless bird)
'endless complaint' is the wordplay.
'endless' means to remove the last letter.
'complaint' becomes 'moan' (a moan is a complaint or objection).
'moan' with its last letter taken away is 'MOA'.
(Other definitions for moa that I've seen before include "Bird no longer" , "Bird's gone for ever" , "was hunted by Maori" , "Bird lost" , "Extinct flightless NZ_bird" .)