Adjustable seats are an advantage (5)
I believe the answer is:
asset
'an advantage' is the definition.
(I've seen this before)
'adjustable seats' is the wordplay.
'adjustable' is an anagram indicator.
'seats' is an anagram of 'ASSET'.
'are' is the link.
(Other definitions for asset that I've seen before include "Useful or valuable quality or possession" , "Something well worth having" , "Someone or something of value" , "Valued item" , "A possession of some value" .)