Adjustment for Heathrow's terminal during take-off (5)
I believe the answer is:
tweak
'adjustment' is the definition.
(I have seen 'Fine adjustment ' mean 'tweak' so perhaps 'adjustment' could also mean 'tweak')
'heathrow's terminal during take-off' is the wordplay.
'terminal' indicates one should take the final letters (terminal refers to the end).
'during' indicates putting letters inside.
'off' is an anagram indicator.
The final letter of 'heathrow' is 'w'.
'take' with letters rearranged gives 'teak'.
'w' inserted inside 'teak' is 'TWEAK'.
'for' is the link.
(Other definitions for tweak that I've seen before include "Nip" , "Fine-tune, twist" , "Minor change" , "Change slightly" , "spin, thus?" .)