The system does not always work as it should, MPN 11. When I was at nav school a student was chopped from his course after it was discovered he had been fiddling his astro (basically getting a simple Gee fix and then back calculating figures as though he had obtained the fix by astro). This was rightly deemed to be a matter of integrity, not competence. However rather than being chucked out on his ear the chap was offered a transfer to the RAF Regiment, which he took.
I was still wearing RAF Regiment flashes at the time, and when I put forward my opinion that if someone lacked the integrity to be a navigator, why would he be deemed to be ok to be a Regiment officer, where he may be responsible for men's lives. The staff member I put this to basically told me to wind my neck in and mind my own business. I have no idea how said astro fiddler made out as a Regiment officer, but it rankled at the time.