Flying Grading does exactly what it says on the tin i.e. it grades people into those who are likely to pass subsequent flying training and those who are not. Whilst aptitude tests show whether a person has the aptitude to perform aircrew tasks, it cannot test the persons ability to perform in the air. As most of us know once you strap into an aircraft, especially under training, most of your brain power disappears. Logically people should undergo aircrew testing then flying grading before joining the services, but this would be very expensive. Of course FG cannot prove to be perfect as people still get chopped along the way, but it does 'weed out' those likely to fail at an early stage. The very old and sometimes quite bold pilots who did FG at Roborough reckoned they could tell on the first flight whether someone would be able to hack further training. Luckily for me we were allowed a full 13 hours, which included a magical solo in a Chipmunk ah Happy Days!