It's essential to a helicopter going up or down (5)
I believe the answer is:
rotor
'up or down' is the definition.
'it's essential to a helicopter going' is the wordplay.
I cannot really see how this works, but
'to' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for rotor that I've seen before include "Dynamo part" , "Arm moving" , "Revolving arm in machine" , "It goes around" , "Turning part of machine - a palindrome" .)