Where there are no seats in first class, winter transport cut (5)
I believe the answer is:
aisle
'where there are no seats' is the definition.
(rows of seats might be divided by an aisle)
'first class winter transport cut' is the wordplay.
'first class' becomes 'ai' (A1 - top quality).
'winter transport' becomes 'sled' (I've seen this in another clue).
'cut' means to remove the last letter.
'sled' with its final letter removed is 'sle'.
'ai'+'sle'='AISLE'
'in' acts as a link.
(Other definitions for aisle that I've seen before include "Passage between shelves in supermarket" , "Passageway between pews" , "Passage between pews" , "channel" , "Church walkway" .)