Aircraft mechanic initially breaks spanner in the works (5)
I believe the answer is:
blimp
'aircraft' is the definition.
(blimp is a kind of aircraft)
'mechanic initially breaks spanner in the works' is the wordplay.
'initially' suggests taking the first letters.
'breaks' is an insertion indicator.
'spanner in the works' becomes 'blip' (I can't explain this - if you can you should give a lot more credence to this answer).
The first letter of 'mechanic' is 'm'.
'm' put within 'blip' is 'BLIMP'.
Can you help me to learn more?
(Other definitions for blimp that I've seen before include "aircraft" , "needs cover when shooting" , "David Low's cartoon colonel - airship used for publicity" , "full of hot air?" , "Pompous type - barrage balloon" .)