I recall in the mid 80s a Re-role Nav Student who was chopped on his final trip on the OCU for "Safety. He had been on review and given extra hours on every phase of the course. Each time Group over-rode the OCU Staff decision and approved the extra Sims and Flying.
On the final trip the poor chap (8000+ hours and 36 years old) was told that he had failed the course. On the final trip he would have allowed his pilot to fly them both into the sea in blissful ignorance. Afterwards he has relieved that it was all over. 16 years of AEW is not a great lead-in to becoming a Fast Jet Nav.
Sometimes very difficult decisions have to be made. That is how we earned the extra "Instructional Pay"!