Narrative:

On jet route from sav approaching the bitho 6 arrival into mco on a 1000 FPM descent through FL280 on LNAV and vertical speed engaged with autoplt on, aircraft made a hard roll to left. Overrode autoplt at approximately 30 degrees left bank and aircraft began to roll back right towards level flight. Apparently pressure I applied began to relax somewhat and began another hard roll to the left. At this point I disconnected the autoplt and the first officer disconnected the yaw damper. The aircraft was rolled back wings level and control was restored. Several moments later I reconnected the yaw damper as there were no yaw tendencies whatsoever. The autoplt remained off and I landed the aircraft without further incident at mco. Although some passenger were startled momentarily, the incident passed very quickly per the flight attendants observations and there were no injuries. All proper auths were notified and appropriate reports have been written and submitted. An extensive conference call was made immediately after the incident and there was a conference held after my return to pit the next day. Myself and the first officer were attentive to our duties during the flight and recovery was made rapidly. The entire incident lasted, in my opinion at the time, less then 5 seconds. Callback conversation with reporter revealed the following: the reporter said he thought the cause of the problem was an unexplained uncommanded autoplt abruptly rapid left roll input. As per procedure the yaw damper was immediately and reflexively turned off by the first officer at the onset of the roll. This did not correct the problem. The captain flying at the same time grabbed the wheel and over rode the autoplt to bring the wings level from a 20 to 30 degree left bank. The autoplt thereby defaulted to control wheel steering. When the wings were level the captain relaxed his pressure on the control wheel whereupon the airplane again commenced its abruptly rapid left roll. The captain disconnected the autoplt completely and hand flew the airplane. The remainder of the flight was normal with the yaw damper turned back on and the autoplt left off. There were no injuries, but, the flight attendants and passenger were startled. If the reporter had the event to happen again he would be quicker about disconnecting the autoplt and more attentive to consoling the passenger and flight attendants. He suggested pilots be encouraged to personally evaluate their own hand flying currency to assure their hand flying proficiency continually exists. The flight data recorder tape was read and the airplane rolled to a bank angle of 22 degrees. The PF response to the onset of the roll was virtually instantaneous as he was 'tweaking' (making small adjustments to) the throttles at the moment of onset of the roll and immediately grabbed the wheel. There was no wake turbulence encounter.

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Original NASA ASRS Text

Title: A BOEING 737-300 ROLLS RAPIDLY TO THE L DURING NORMAL DSCNT.

Narrative: ON JET RTE FROM SAV APCHING THE BITHO 6 ARR INTO MCO ON A 1000 FPM DSCNT THROUGH FL280 ON LNAV AND VERT SPD ENGAGED WITH AUTOPLT ON, ACFT MADE A HARD ROLL TO L. OVERRODE AUTOPLT AT APPROX 30 DEGS L BANK AND ACFT BEGAN TO ROLL BACK R TOWARDS LEVEL FLT. APPARENTLY PRESSURE I APPLIED BEGAN TO RELAX SOMEWHAT AND BEGAN ANOTHER HARD ROLL TO THE L. AT THIS POINT I DISCONNECTED THE AUTOPLT AND THE FO DISCONNECTED THE YAW DAMPER. THE ACFT WAS ROLLED BACK WINGS LEVEL AND CTL WAS RESTORED. SEVERAL MOMENTS LATER I RECONNECTED THE YAW DAMPER AS THERE WERE NO YAW TENDENCIES WHATSOEVER. THE AUTOPLT REMAINED OFF AND I LANDED THE ACFT WITHOUT FURTHER INCIDENT AT MCO. ALTHOUGH SOME PAX WERE STARTLED MOMENTARILY, THE INCIDENT PASSED VERY QUICKLY PER THE FLT ATTENDANTS OBSERVATIONS AND THERE WERE NO INJURIES. ALL PROPER AUTHS WERE NOTIFIED AND APPROPRIATE RPTS HAVE BEEN WRITTEN AND SUBMITTED. AN EXTENSIVE CONFERENCE CALL WAS MADE IMMEDIATELY AFTER THE INCIDENT AND THERE WAS A CONFERENCE HELD AFTER MY RETURN TO PIT THE NEXT DAY. MYSELF AND THE FO WERE ATTENTIVE TO OUR DUTIES DURING THE FLT AND RECOVERY WAS MADE RAPIDLY. THE ENTIRE INCIDENT LASTED, IN MY OPINION AT THE TIME, LESS THEN 5 SECONDS. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: THE RPTR SAID HE THOUGHT THE CAUSE OF THE PROB WAS AN UNEXPLAINED UNCOMMANDED AUTOPLT ABRUPTLY RAPID L ROLL INPUT. AS PER PROC THE YAW DAMPER WAS IMMEDIATELY AND REFLEXIVELY TURNED OFF BY THE FO AT THE ONSET OF THE ROLL. THIS DID NOT CORRECT THE PROB. THE CAPT FLYING AT THE SAME TIME GRABBED THE WHEEL AND OVER RODE THE AUTOPLT TO BRING THE WINGS LEVEL FROM A 20 TO 30 DEG L BANK. THE AUTOPLT THEREBY DEFAULTED TO CTL WHEEL STEERING. WHEN THE WINGS WERE LEVEL THE CAPT RELAXED HIS PRESSURE ON THE CTL WHEEL WHEREUPON THE AIRPLANE AGAIN COMMENCED ITS ABRUPTLY RAPID L ROLL. THE CAPT DISCONNECTED THE AUTOPLT COMPLETELY AND HAND FLEW THE AIRPLANE. THE REMAINDER OF THE FLT WAS NORMAL WITH THE YAW DAMPER TURNED BACK ON AND THE AUTOPLT LEFT OFF. THERE WERE NO INJURIES, BUT, THE FLT ATTENDANTS AND PAX WERE STARTLED. IF THE RPTR HAD THE EVENT TO HAPPEN AGAIN HE WOULD BE QUICKER ABOUT DISCONNECTING THE AUTOPLT AND MORE ATTENTIVE TO CONSOLING THE PAX AND FLT ATTENDANTS. HE SUGGESTED PLTS BE ENCOURAGED TO PERSONALLY EVALUATE THEIR OWN HAND FLYING CURRENCY TO ASSURE THEIR HAND FLYING PROFICIENCY CONTINUALLY EXISTS. THE FLT DATA RECORDER TAPE WAS READ AND THE AIRPLANE ROLLED TO A BANK ANGLE OF 22 DEGS. THE PF RESPONSE TO THE ONSET OF THE ROLL WAS VIRTUALLY INSTANTANEOUS AS HE WAS 'TWEAKING' (MAKING SMALL ADJUSTMENTS TO) THE THROTTLES AT THE MOMENT OF ONSET OF THE ROLL AND IMMEDIATELY GRABBED THE WHEEL. THERE WAS NO WAKE TURB ENCOUNTER.

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.