Long-distance traveller turns to AA, breaking down (9)
I believe the answer is:
astronaut
'long-distance traveller' is the definition.
'astronaut' can be an answer for 'traveller' (astronaut is a kind of traveller). I'm not sure about the 'long-distance' bit.
'turns to aa breaking down' is the wordplay.
'breaking down' is an anagram indicator.
'turns'+'to'+'aa'='turnstoaa'
'turnstoaa' is an anagram of 'ASTRONAUT'.
Can you help me to learn more?
(Other definitions for astronaut that I've seen before include "Santa tour for space traveller" , "Space explorer" , "For member of high-flying mission" , "heavenly voyager" , "Person trained to travel in a spacecraft" .)