Abandon plane and sit back working (8)
I believe the answer is:
jettison
'abandon' is the definition.
(thesaurus)
'plane and sit back working' is the wordplay.
'plane' becomes 'jet' (jet plane is a kind of plane).
'and' means one lot of letters go next to another.
'back' says the letters should be written in reverse.
'working' becomes 'on'.
'sit' back-to-front is 'tis'.
'jet'+'tis'+'on'='JETTISON'
(Other definitions for jettison that I've seen before include "Throw away (from ship or aeroplane?)" , "21 [OFFLOAD]" , "Form of motor racing" , "Throw goods overboard, or discard what is unwanted" , "Abandon or throw overboard" .)