CAAS requires min 5 "O" levels at one attempt. Even if u get a strings of A's in "A" levels, CAAS still requires the above.
If u think of getting a degree and over ride the "O"levels results, it doesn't work! A degree in aeronautical study even from prestigious Embryl Rydell (correct spelling?) might open doors to interview only....
May be more info in SIA cadets thread.... good luck!