NMAC BTWN AN SMT TRAINING FLT ON FINAL AND ANOTHER ACFT TURNED BASE TO FINAL BY TWR CTLR TOO EARLY FOR SEPARATION WITH RPTR ACFT X.

Narrative

I ESTABLISHED ACFT X ON THE ILS LOC/GS TO RWY 28L AND WAS CLRED FOR THE STRAIGHT-IN TO RWY 28L BY PDX ATC (126.9 MHZ). SHORTLY THEREAFTER; I WAS HANDED OFF TO PDX TWR ON 123.77 MHZ WHO CLRED ME TO LAND BEHIND ACFT Z ON SHORT FINAL. (I RPTED THAT ACFT IN SIGHT AS REQUESTED.) ACFT Y WAS S OF THE ARPT COMPLEX ENTERING ON THE L DOWNWIND FOR RWY 28L. THE PDX TWR CTLR FIRST INSTRUCTED ACFT Y TO TURN BASE (I THINK THEY WERE ATTEMPTING TO PUT HIM BTWN MYSELF AND THE BE99 OVER THE NUMBERS). AS ACFT Y STARTED THE TURN; THE PDX TWR CTLR INSTRUCTED ACFT Y TO DISREGARD THE PREVIOUS INSTRUCTION; TURN BACK TO THE DOWNWIND; AND PLAN TO TURN BASE JUST E OF ROCKY BUTTE (WOULD RESULT IN AN APPROX 2 MI BASE TURN). AS I DSNDED THROUGH 1000 FT AND ABOUT 3 MI FINAL; THE PDX TWR CTLR AGAIN INSTRUCTED ACFT Y TO TURN BASE. ACFT Y WAS ALREADY CLOSER IN THAN USUAL DUE TO THE PREVIOUS MANEUVERS AND ABOVE ME WHEN HE STARTED THE TURN. 2 THINGS BECAME APPARENT: 1) THE PDX TWR CTLR MADE AN ERROR IN ISSUING A BASE TURN INSTRUCTION TO ACFT Y AT THAT TIME. 2) THE PLT OF ACFT Y HAD LOST SIGHT OF MY ACFT ON FINAL (PROBABLY UNDER HIS NOSE STRUCTURE); AND/OR ASSUMED THAT I WAS FURTHER DOWN THE FINAL APCH THAN I ACTUALLY WAS. MY REACTION WAS TO CALL THIS TO THE ATTN OF THE PDX TWR CTLR AS SOON AS THE RADIO WAS CLR BY SAYING 'PORTLAND TWR; THIS ISN'T GOING TO WORK; ACFT X.' MOMENTS LATER (AS ACFT X WAS TURNING FINAL AND PARALLELING MY ACFT A FEW HUNDRED FT ABOVE AND TO THE S); THE PDX TWR CTLR ISSUED INSTRUCTIONS TO ACFT Y TO MAINTAIN ALT AND TURN L TO RE-ENTER THE DOWNWIND FOR RWY 28L; WHICH HE PROMPTLY DID. THE CLOSEST PROX BTWN THE 2 ACFT WAS APPROX 300 FT VERTLY AND 500 FT HORIZLY. THE RELATIVE MOTION OF THE 2 ACFT DID NOT INDICATE AN IMPENDING COLLISION.