Took off in feat crossing channel (8)
I believe the answer is:
deducted
'took off' is the definition.
('deduct' can be a synonym of 'take off')
'feat crossing channel' is the wordplay.
'feat' becomes 'deed' ('deed' can be a synonym of 'feat'**).
'crossing' is an insertion indicator.
'channel' becomes 'duct' ('duct' can be a synonym of 'channel').
'deed' placed around 'duct' is 'DEDUCTED'.
'in' is the link.
(Other definitions for deducted that I've seen before include "Taken away (from)" , "Taken off (from sum)" , "Subtracted" .)