A320 CREW ENCOUNTERED MODERATE TO SEVERE WAKE TURB FROM A B757 8 MI AHEAD IN PDX CLASS E AIRSPACE.

Narrative

ON BONVL 4 ARR; WHILE FOLLOWING DSCNT PROFILE; A B757 INTERCEPTED PROFILE ABOUT 8 NM AHEAD. CONTINUING DOWN THE PROFILE; OUR ACFT EXPERIENCED 3 CASES OF WAKE TURB AT LEAST MODERATE IN NATURE; AND WITH MOMENTARY LOSSES OF CTL ON 2 OCCASIONS. WE WERE FLYING 250 KTS; ON THE PROFILE; SPD BREAK EXTENDED ON FIRST OCCASION; NONE AFTER. WE EXPERIENCED THE TURB AT ABOUT 13000 FT THE FIRST TIME; AND AROUND 8000 FT. THE FINAL INCIDENT. WE CONTINUED WELL ABOVE THE PROFILE AND VECTORED LATERALLY AWAY FROM THE B757. THIS WAS COORD WITH ATC. THE LNDG WAS UNEVENTFUL. IN 2 OF 3 OCCASIONS; ROLL WAS MOMENTARILY UNCTLABLE; AND THE ACFT WENT TO AROUND 30 UNTIL CTL WAS RESTORED; WINDS WERE 280 DEGS AT 15-20 KTS; A DIRECT HEADWIND; CLR SKIES. THE OTHER ACFT WAS ACR Y. I DISCUSSED THIS WITH CREW MEMBERS ABOARD ACR Y. THEY WERE ON PROFILE; 250 KTS; FULL SPD BRAKES EXTENDED AT 180000 LB WT. THEY MAINTAINED SPD TO A 6 MI FINAL AND HAD BRAKES EXTENDED TO 4 MI. THEY ALSO NOTED IT UNUSUAL THAT A WAKE TURB ENCOUNTER WOULD OCCUR AT 8 NM SEPARATION AT THAT SEVERITY. CREW COORD THROUGHOUT WAS EXCELLENT; AS WAS THE COOPERATION OF OTHER CREW. THE NECESSITY OF THIS RPT WAS DICTATED BY THE SEVERITY OF THE ENCOUNTER AND THE LARGE SEPARATION OF ACFT; WHICH MADE IT AN UNUSUAL OCCURRENCE.