Narrative:

On bonvl 4 arrival, while following descent profile, a B757 intercepted profile about 8 NM ahead. Continuing down the profile, our aircraft experienced 3 cases of wake turbulence at least moderate in nature, and with momentary losses of control on 2 occasions. We were flying 250 KTS, on the profile, speed break extended on first occasion, none after. We experienced the turbulence 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 coordination with ATC. The landing was uneventful. In 2 of 3 occasions, roll was momentarily uncontrollable, and the aircraft went to around 30 until control was restored, winds were 280 degrees at 15-20 KTS, a direct headwind, clear skies. The other aircraft was air carrier Y. I discussed this with crew members aboard air carrier Y. They were on profile, 250 KTS, full speed brakes extended at 180000 pound weight. They maintained speed to a 6 mi final and had brakes extended to 4 mi. They also noted it unusual that a wake turbulence encounter would occur at 8 NM separation at that severity. Crew coordination throughout was excellent, as was the cooperation of other crew. The necessity of this report was dictated by the severity of the encounter and the large separation of aircraft, which made it an unusual occurrence.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.