In aviation, it indicates a point along the route (3)
I believe the answer is:
via
'a point along the route' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'in aviation it' is the wordplay.
'in' indicates a hidden word.
'VIA' is hidden within 'aviation it'.
'indicates' is the link.
Can you help me to learn more?
(Other definitions for via that I've seen before include "By way of - in Latin" , "Roman road" , "By means of" , "Passing through" , "Going through" .)