The system has changed somewhat over the years and the
clever lucky ones have managed to stay on top of it all.
Imagine hitting 55yo on the top rate of PA spine salary having flown virtually non-stop for 35 years, getting your pension (which also took account of "flying pay" which was part of your salary now and therefore pensionable) then moving across to FTRS to do exactly the same job, get the same take-home pay (FTRS salary + abated pension) as you had as a Regular then someone gives you flying pay on top of that!
Lucky buggers!