Opportunity to be in the open air is a remote possibility (7,6)
I believe the answer is:
outside chance
'a remote possibility' is the definition.
(thesaurus)
'opportunity to be in the open air' is the wordplay.
'opportunity' becomes 'chance' (synonyms).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'be in the open air' becomes 'outside' (I've seen this in another clue).
'chance' put after 'outside' is 'OUTSIDE CHANCE'.
'is' acts as a link.
(Other definitions for outside chance that I've seen before include "one at long odds" , "It might just happen" , "smallest likelihood" .)