Pilot going astray in marina (6)
I believe the answer is:
airman
'pilot' is the definition.
(someone who flies aircraft)
'going astray in marina' is the wordplay.
'going astray in' is an anagram indicator.
'marina' with letters rearranged gives 'AIRMAN'.
(Other definitions for airman that I've seen before include "He flies" , "Pilot" , "crew member" , "Flier" , "Male flyer" .)