Melchett,
Under FAFPS, your pension will be based on your career average from the date the scheme is introduced (from Apr 15). As you say, past service is covered by your accrued rights. It will only be those who join the Services from Apr 15 and build up only a FAFPS pension who will really be on a 'Career Average'. As for PAS, it is not SP therefore PAS pensions under FAFPS will be based on pensionable pay.
Rev