Transport company describes very thin crack making left wing detach (7)
I believe the answer is:
airline
'transport' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for airline that I've seen before include "Virgin, possibly" , "Business taking off" , "Transport organisation" , "EasyJet, for example" , "Company operating flying machines" .)