Careful of the short gap at end of runway (7)
I believe the answer is:
thrifty
'careful' is the definition.
('thrifty' can be a synonym of 'careful')
'the short gap at end of runway' is the wordplay.
'short' means to remove the last letter.
'gap' becomes 'rift' (rift is a kind of gap**).
'at end of' indicates one should take the final letters.
The last letter of 'runway' is 'y'.
'the' with its last letter taken off is 'th'.
'th'+'rift'+'y'='THRIFTY'
'of' acts as a link.
(Other definitions for thrifty that I've seen before include "Conserving" , "Frugal - economical" , "Not extravagant" , "Sparing" , "Careful with money" .)