On the PA Spine, your flying pay is added to your basic pay and is paid as one amount as opposed to getting basic pay plus flying pay (two separate amounts).
Your flying pay is not added to your basic pay on the PAS. It is a totally separate pay scale that somebody on it can earn in excess of what they would have received if they were on the normal pay scales. There 35 levels that go all the way up to to £75000. Not bad if you can reach this level as a Flt Lt. Even NCA Masters can earn £58000. As a Master Aircrew on 44500 + the top rate flying pay this only equates to £51500 and a Flight Sergeant on the PAS can earn £54000 which equates to level 9 Sqn Ldr. So all those Ground branch Sqn Ldr's who have worked hard to get where they are are probably earning less than a FS/Macr PAS NCA.