Crossword Genius

The old aircraft turning to land - or take off (8)

Ross

I believe the answer is:

subtract

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'take off' is the definition.
(I know that take off can be written as subtract)

'the old aircraft turning to land' is the wordplay.
'the old aircraft turning' becomes 'sub' (I can't explain this - if you can you should give a lot more credence to this answer).
'to land' becomes 'tract' (tract can mean an area of land).
'sub'+'tract'='SUBTRACT'

'or' is the link.

Can you help me to learn more?

(Other definitions for subtract that I've seen before include "Withdraw" , "Knock off" , "dock" , "Take away (a number)" , "Remove" .)

I've seen this clue in the Evening Standard.
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