Attempt to join RAF on way up? Succeed (2,3)
I believe the answer is:
go far
'succeed' is the definition.
(going far is a kind of succeeding)
'attempt to join raf on way up?' is the wordplay.
'attempt' becomes 'go' (go is a kind of attempt).
'to join' is a charade indicator (letters next to each other).
'on way up?' says the letters should be written backwards (I've seen 'on way up' mean this).
'raf' reversed gives 'far'.
'go'+'far'='GO FAR'
(Other definitions for go far that I've seen before include "flourish?" , "Last" , "Achieve considerable success" , "Achieve great things" , "Make real progress, achieve much" .)