Sub rising to ventilate sees plane (6)
I believe the answer is:
airbus
'plane' is the definition.
'sub rising to ventilate' is the wordplay.
'rising' says the letters should be written in reverse (going up in a down clue).
'to' means one lot of letters go next to another (I've seen this in other clues).
'ventilate' becomes 'air' (synonyms).
'sub' written backwards gives 'bus'.
'bus' put after 'air' is 'AIRBUS'.
'sees' acts as a link.
(Other definitions for airbus that I've seen before include "Commercial passenger plane" , "European manufacturer of the A380, the world's largest passenger jet" , "plane - with 27d" .)