Breakdown finally in short journey: getting AA (5)
I believe the answer is:
milne
'aa' is the definition.
(AA Milne)
'breakdown finally in short journey' is the wordplay.
'finally' suggests the final letters.
'in' is an insertion indicator.
'short journey' becomes 'mile'.
The final letter of 'breakdown' is 'n'.
'n' inserted into 'mile' is 'MILNE'.
'getting' acts as a link.
(Other definitions for milne that I've seen before include "He wrote stories for his son, Christopher Robin" , "Winnie-the-Pooh author" , "A.A. --, Pooh creator" , "A.A. -, Pooh author" , "Children's author" .)