Takes plane (American), which lands in the sea (6)
I believe the answer is:
jetsam
'which lands in the sea' is the definition.
'takes plane american' is the wordplay.
'takes plane' becomes 'jets'.
'american' becomes 'am' (abbreviation in some contexts).
'jets'+'am'='JETSAM'
(Other definitions for jetsam that I've seen before include "Floating rubbish" , "Flotsam and --" , "Rubbish on shore thrown from ships" , "Goods thrown into the sea" , "Discarded objects washed ashore" .)