Rusty Cessna, basing comments on the fact that you will always get "prime" candidates apply to OASC as soon as they have the acedemic qualifications. It normally follows that these are also the people who have always been strongly motivated to join the RAF. Consequently, these guys and girls have the highest percentage pass mark going through Cranwell officer training. Conversely, at the "end" of the selection year, the quality/motivation of candidates is lower (OASC Board Grades measurably less), so, not surprisingly, lower first time pass mark at DIOT.