For airmen, hopping on this is a low practice (5)
I believe the answer is:
hedge
This clue might be a double definition.
'for airmen hopping on this' is the first definition.
The definition suggests a singular noun which matches the answer.
'low practice' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'is a' acts as a link.
Can you help me to learn more?
(Other definitions for hedge that I've seen before include "Growing division" , "Financial contract" , "Fence of bushes or shrubs" , "take evasive action" , "Beg the question" .)