Narrative:

At cruise, FL330, autoplt engaged, aircraft began to buffet. Captain was PF. He immediately put his hands on the controls. Suddenly, without warning, aircraft encountered severe turbulence and began to quickly roll left. Captain disengaged autoplt and began to apply opposite control (to right). Roll left increased, turbulence increased. Captain steadily increased (to right) opposite control to no avail. Aircraft continued to roll left. Captain recognized that he would quickly run out of opposite control and began a rapid descent. I immediately notified ATC of our descent and why (at FL328). After we stabilized, around FL326, we were cleared to FL290 and continued our descent. Conferring with ATC, we found that a heavy A300 was 10 mi ahead of us at FL330. We think we encountered the A300 wake. No other aircraft in the area reported severe turbulence. After several mins, we were cleared back to FL330, on a course diverging the A300's. Flight continued and was completed with no further incident. Callback conversation with reporter revealed the following information: reporter participated in the wake turbulence callback study. Reporter stated the suddenness of the event is what startled them. Aircraft went up 200 ft and rolled 45 degrees left even though full opposite aileron was applied. Aircraft then descended about 800 ft from there. Captain let it descend hoping to get out of whatever wake they were in. After regaining control of the aircraft, the flight crew then requested lower altitude, and a short vector to the side of the airway. They also slowed down. After the separation increased from the A300, the flight crew climbed back to flight plan cruise altitude and the flight was completed with no further turbulent events. Supplemental information from acn 417172: shortly after leveloff at FL330, in long range cruise, autoplt engaged, aircraft began to shudder. I immediately reduced power as it felt like the onset of mach buffet. As the buffeting intensified, the aircraft began to roll left despite the autoplt effort to maintain straight and level flight. As the roll to the left increased, I disconnected the autoplt, lowered the nose and rolled the aircraft back to wings level. We immediately notified ZLA that we were descending, had encountered extreme turbulence, and requested clearance to FL290. After descending 400 ft, the turbulence subsided. We asked ATC if we were following a heavy aircraft. We were informed that we were 10 mi in trail of an airbus 300. An off course vector was assigned and we eventually returned to FL330. Flight continued uneventfully to our destination.

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Original NASA ASRS Text

Title: B737-300 ENCOUNTERED WAKE TURB FROM A PRECEDING A300 IN ZLA AIRSPACE. THE B737-300 EVALUATES IT AS A SEVERE OCCURRENCE. NO INJURIES OR DAMAGE OCCURRED.

Narrative: AT CRUISE, FL330, AUTOPLT ENGAGED, ACFT BEGAN TO BUFFET. CAPT WAS PF. HE IMMEDIATELY PUT HIS HANDS ON THE CTLS. SUDDENLY, WITHOUT WARNING, ACFT ENCOUNTERED SEVERE TURB AND BEGAN TO QUICKLY ROLL L. CAPT DISENGAGED AUTOPLT AND BEGAN TO APPLY OPPOSITE CTL (TO R). ROLL L INCREASED, TURB INCREASED. CAPT STEADILY INCREASED (TO R) OPPOSITE CTL TO NO AVAIL. ACFT CONTINUED TO ROLL L. CAPT RECOGNIZED THAT HE WOULD QUICKLY RUN OUT OF OPPOSITE CTL AND BEGAN A RAPID DSCNT. I IMMEDIATELY NOTIFIED ATC OF OUR DSCNT AND WHY (AT FL328). AFTER WE STABILIZED, AROUND FL326, WE WERE CLRED TO FL290 AND CONTINUED OUR DSCNT. CONFERRING WITH ATC, WE FOUND THAT A HVY A300 WAS 10 MI AHEAD OF US AT FL330. WE THINK WE ENCOUNTERED THE A300 WAKE. NO OTHER ACFT IN THE AREA RPTED SEVERE TURB. AFTER SEVERAL MINS, WE WERE CLRED BACK TO FL330, ON A COURSE DIVERGING THE A300'S. FLT CONTINUED AND WAS COMPLETED WITH NO FURTHER INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN THE WAKE TURB CALLBACK STUDY. RPTR STATED THE SUDDENNESS OF THE EVENT IS WHAT STARTLED THEM. ACFT WENT UP 200 FT AND ROLLED 45 DEGS L EVEN THOUGH FULL OPPOSITE AILERON WAS APPLIED. ACFT THEN DSNDED ABOUT 800 FT FROM THERE. CAPT LET IT DSND HOPING TO GET OUT OF WHATEVER WAKE THEY WERE IN. AFTER REGAINING CTL OF THE ACFT, THE FLC THEN REQUESTED LOWER ALT, AND A SHORT VECTOR TO THE SIDE OF THE AIRWAY. THEY ALSO SLOWED DOWN. AFTER THE SEPARATION INCREASED FROM THE A300, THE FLC CLBED BACK TO FLT PLAN CRUISE ALT AND THE FLT WAS COMPLETED WITH NO FURTHER TURBULENT EVENTS. SUPPLEMENTAL INFO FROM ACN 417172: SHORTLY AFTER LEVELOFF AT FL330, IN LONG RANGE CRUISE, AUTOPLT ENGAGED, ACFT BEGAN TO SHUDDER. I IMMEDIATELY REDUCED PWR AS IT FELT LIKE THE ONSET OF MACH BUFFET. AS THE BUFFETING INTENSIFIED, THE ACFT BEGAN TO ROLL L DESPITE THE AUTOPLT EFFORT TO MAINTAIN STRAIGHT AND LEVEL FLT. AS THE ROLL TO THE L INCREASED, I DISCONNECTED THE AUTOPLT, LOWERED THE NOSE AND ROLLED THE ACFT BACK TO WINGS LEVEL. WE IMMEDIATELY NOTIFIED ZLA THAT WE WERE DSNDING, HAD ENCOUNTERED EXTREME TURB, AND REQUESTED CLRNC TO FL290. AFTER DSNDING 400 FT, THE TURB SUBSIDED. WE ASKED ATC IF WE WERE FOLLOWING A HVY ACFT. WE WERE INFORMED THAT WE WERE 10 MI IN TRAIL OF AN AIRBUS 300. AN OFF COURSE VECTOR WAS ASSIGNED AND WE EVENTUALLY RETURNED TO FL330. FLT CONTINUED UNEVENTFULLY TO OUR DEST.

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.