Air ships go off-course, finding rocky reef (6)
I believe the answer is:
skerry
'rocky reef' is the definition.
The definition suggests a singular noun which matches the answer.
'air ships go off-course' is the wordplay.
'air' becomes 'sky'.
'ships' means one lot of letters goes inside another (to ship can mean to carry or transport something).
'go off course' becomes 'err' (I've seen this in another clue).
'sky' placed around 'err' is 'SKERRY'.
'finding' is the link.
Can you help me to learn more?
(Other definitions for skerry that I've seen before include "tiny island" , "small island" , "Rocky island or reef" .)