Old plane nearly late — the cause of serious bird strike? (7)
I believe the answer is:
bustard
'cause of serious bird strike?' is the definition.
(large bird which might strike a plane)
'old plane nearly late' is the wordplay.
'old plane' becomes 'bus' (bus could once mean a passenger plane).
'nearly' means to remove the last letter.
'late' becomes 'tardy' (synonyms).
'tardy' with its final letter taken away is 'tard'.
'bus'+'tard'='BUSTARD'
'the' acts as a link.
(Other definitions for bustard that I've seen before include "Bad rust (anag.)" , "Long-legged, heavy-bodied bird" , "Large heavy bird" , "See large bird" , "flyer" .)