Narrative:

Aircraft encountered moderate turbulence south of orf VOR and was slowed to mach .70 with permission of ATC. The aircraft then began dutch rolling back and forth about 5-10 degree bank either side of level. After several mins the aircraft rolled hard right in a 30 degree bank and immediately rolled back to the left in a 30 degree bank. In the process of the first hard right bank the autoplt tripped off. While I struggled to keep level, the aircraft descended about 300-400 ft even though we were pitched nose up with additional power. I regained control with priority to attaining level flight and I then encountered less turbulence. A climb back to FL330 was initiated and ATC was advised as to our situation. The strange part is that at no time was the turbulence more then moderate, but the rocking force was extremely strong and could not be overcome. I don't know if it could be categorized as clear air turbulence, I don't think so, but it was a strange encounter. Several other aircraft experienced the same rolling turbulence, but not as severe as we did. Supplemental information from acn 391524: reported unable to hold to altitude to ATC. ATC gave us a turn off course and descent to lower altitude.

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Original NASA ASRS Text

Title: CAPT OF A B737-200 MOMENTARILY LOST CTL OF THE ACFT IN MODERATE TURB DURING HIGH ALT CRUISE DUE TO UNCONTROLLABLE LATERAL ROLLING AND LOSS OF ALT EVEN IN A NOSE UP ATTITUDE. ATC RESPONDED TO THEIR SIT BY TURNING THEM OFF THE AIRWAY UNTIL CTL COULD BE REGAINED, UPON WHICH THEY RETURNED TO ASSIGNED ALT.

Narrative: ACFT ENCOUNTERED MODERATE TURB S OF ORF VOR AND WAS SLOWED TO MACH .70 WITH PERMISSION OF ATC. THE ACFT THEN BEGAN DUTCH ROLLING BACK AND FORTH ABOUT 5-10 DEG BANK EITHER SIDE OF LEVEL. AFTER SEVERAL MINS THE ACFT ROLLED HARD R IN A 30 DEG BANK AND IMMEDIATELY ROLLED BACK TO THE L IN A 30 DEG BANK. IN THE PROCESS OF THE FIRST HARD R BANK THE AUTOPLT TRIPPED OFF. WHILE I STRUGGLED TO KEEP LEVEL, THE ACFT DSNDED ABOUT 300-400 FT EVEN THOUGH WE WERE PITCHED NOSE UP WITH ADDITIONAL PWR. I REGAINED CTL WITH PRIORITY TO ATTAINING LEVEL FLT AND I THEN ENCOUNTERED LESS TURB. A CLB BACK TO FL330 WAS INITIATED AND ATC WAS ADVISED AS TO OUR SIT. THE STRANGE PART IS THAT AT NO TIME WAS THE TURB MORE THEN MODERATE, BUT THE ROCKING FORCE WAS EXTREMELY STRONG AND COULD NOT BE OVERCOME. I DON'T KNOW IF IT COULD BE CATEGORIZED AS CLR AIR TURB, I DON'T THINK SO, BUT IT WAS A STRANGE ENCOUNTER. SEVERAL OTHER ACFT EXPERIENCED THE SAME ROLLING TURB, BUT NOT AS SEVERE AS WE DID. SUPPLEMENTAL INFO FROM ACN 391524: RPTED UNABLE TO HOLD TO ALT TO ATC. ATC GAVE US A TURN OFF COURSE AND DSCNT TO LOWER ALT.

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.