Passable as its new assembly line (12)
I believe the answer is:
satisfactory
'passable' is the definition.
(similar in meaning)
'as its new assembly line' is the wordplay.
'new' is an anagram indicator.
'assembly line' becomes 'factory' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'as'+'its'='asits'
'asits' with letters rearranged gives 'satis'.
'satis'+'factory'='SATISFACTORY'
Can you help me to learn more?
(Other definitions for satisfactory that I've seen before include "Good enough" , "Fully acceptable" , "fine" , "OK" , "unexceptional" .)