Narrative:

Our B737-300 was in cruise at FL280. We had visual contact and TCASII on another aircraft at FL290 approximately 8 mi ahead and slightly right (about 1 O'clock). The other aircraft was slowly crossing in front of our path remaining 1000 ft above. As we got to about where his path would have been over ours, we experienced a periodic buffet on our right wing for about 4 seconds followed by a loss of lift on the right wing with the aircraft rolling about 35 degrees right wing down. The autoplt was on and held the roll to 35 degrees for a second or 2, then seemed as if it might not be able to maintain, so I kicked off the autoplt and was able to roll wings level after another second or two. I needed about 3/4 aileron input to recover. I asked ZLA what type aircraft that was ahead at FL290 and they replied B757. Callback conversation with reporter revealed the following information: reporter participated in the wake turbulence structured callback program. There was always a 1000 ft vertical separation throughout this incident. The B737 was rolled into a 30 degree right bank, but had enough aileron control to keep the aircraft from rolling further into a steep bank. The flight crew recognized the buffeting on the right wing as a preliminary warning of wake. The captain disconnected the autoplt and applied controls as needed to get wings back to level. When flight crew mentioned to ARTCC they had encountered wake from a B757 several mi ahead, the controller was very surprised, as if wake could not be experienced from a B757 at flight altitudes. This was an event of short duration (5-6 seconds) and of lesser magnitude (2 on a scale of 5).

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Original NASA ASRS Text

Title: A B737-300 FLYING IN ZLA AIRSPACE ENCOUNTERS WAKE TURB WHEN FLYING BEHIND A B757.

Narrative: OUR B737-300 WAS IN CRUISE AT FL280. WE HAD VISUAL CONTACT AND TCASII ON ANOTHER ACFT AT FL290 APPROX 8 MI AHEAD AND SLIGHTLY R (ABOUT 1 O'CLOCK). THE OTHER ACFT WAS SLOWLY XING IN FRONT OF OUR PATH REMAINING 1000 FT ABOVE. AS WE GOT TO ABOUT WHERE HIS PATH WOULD HAVE BEEN OVER OURS, WE EXPERIENCED A PERIODIC BUFFET ON OUR R WING FOR ABOUT 4 SECONDS FOLLOWED BY A LOSS OF LIFT ON THE R WING WITH THE ACFT ROLLING ABOUT 35 DEGS R WING DOWN. THE AUTOPLT WAS ON AND HELD THE ROLL TO 35 DEGS FOR A SECOND OR 2, THEN SEEMED AS IF IT MIGHT NOT BE ABLE TO MAINTAIN, SO I KICKED OFF THE AUTOPLT AND WAS ABLE TO ROLL WINGS LEVEL AFTER ANOTHER SECOND OR TWO. I NEEDED ABOUT 3/4 AILERON INPUT TO RECOVER. I ASKED ZLA WHAT TYPE ACFT THAT WAS AHEAD AT FL290 AND THEY REPLIED B757. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN THE WAKE TURB STRUCTURED CALLBACK PROGRAM. THERE WAS ALWAYS A 1000 FT VERT SEPARATION THROUGHOUT THIS INCIDENT. THE B737 WAS ROLLED INTO A 30 DEG R BANK, BUT HAD ENOUGH AILERON CTL TO KEEP THE ACFT FROM ROLLING FURTHER INTO A STEEP BANK. THE FLC RECOGNIZED THE BUFFETING ON THE R WING AS A PRELIMINARY WARNING OF WAKE. THE CAPT DISCONNECTED THE AUTOPLT AND APPLIED CTLS AS NEEDED TO GET WINGS BACK TO LEVEL. WHEN FLC MENTIONED TO ARTCC THEY HAD ENCOUNTERED WAKE FROM A B757 SEVERAL MI AHEAD, THE CTLR WAS VERY SURPRISED, AS IF WAKE COULD NOT BE EXPERIENCED FROM A B757 AT FLT ALTS. THIS WAS AN EVENT OF SHORT DURATION (5-6 SECONDS) AND OF LESSER MAGNITUDE (2 ON A SCALE OF 5).

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.