Take back what you said the undercarriage would do (7)
I believe the answer is:
retract
'take back' is the definition.
(I've seen this before)
'what you said the undercarriage would do' is the wordplay.
I cannot really see how this works, but
'said' could be 't' (I've seen this in other clues) and 't' is found within the answer.
'do' could be 'act' (I've seen this before) and 'act' is found within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for retract that I've seen before include "Abjure" , "Reverse" , "Withdraw as unjustified" , "Sheathe" , "Pull back (statements or claws, perhaps)" .)