Narrative:

Aircraft made violent yaw to the right, simultaneous muffled boom, and instant roll to the right. Autoplt/autothrottles manually disengaged immediately. Control column forces and displacement to regain control of the aircraft indicated a very serious problem with ctlability. To maintain wings level took 40 degrees left aileron (marked by the index on the wall) rudder forces normal. Aileron forces to the left very heavy. Forces to the right extremely light (or more like normal) as slow as I could fly and maintain control about 160 KTS. Emergency landing made about 18 mins after onset at san pedro sula, honduras. I had quite a lot of difficulty with roll control in that for corrections to the left would take a lot of pressure (for illustration say 20 pounds) for corrections to the right all I had to do was ease off (for illustration say 2 ounces). Fortunately, it was a very clear day and smooth. I feel if I had the normal low level bumpy air I would have possibly gotten behind the control response and lost control of the aircraft. The company, boeing, etc are still in san pedro sula (now 3 days after the incident) inspecting the aircraft. It has been relayed to me that they have been able to duplicate the problem on the ground, but do not know why. The 'a' autoplt paddles disengage but the autoplt itself will not disengage until all power is removed from the aircraft. The yaw damper is exceeding its design limits on its own initiative and putting inputs into the system. After the fact, it appears I was fighting with the autoplt for control of the aircraft. This was a boeing 737-300.

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Original NASA ASRS Text

Title: FLC OF AN ACR B737-300 DECLARED AN EMER AND DIVERTED TO LAND AFTER EXPERIENCING A VIOLENT YAW AND ROLL, TOGETHER WITH HEARING A 'BOOM!' THE ACFT ROLL WAS VERY DIFFICULT TO CTL THROUGHOUT DSCNT TO LAND.

Narrative: ACFT MADE VIOLENT YAW TO THE R, SIMULTANEOUS MUFFLED BOOM, AND INSTANT ROLL TO THE R. AUTOPLT/AUTOTHROTTLES MANUALLY DISENGAGED IMMEDIATELY. CTL COLUMN FORCES AND DISPLACEMENT TO REGAIN CTL OF THE ACFT INDICATED A VERY SERIOUS PROB WITH CTLABILITY. TO MAINTAIN WINGS LEVEL TOOK 40 DEGS L AILERON (MARKED BY THE INDEX ON THE WALL) RUDDER FORCES NORMAL. AILERON FORCES TO THE L VERY HVY. FORCES TO THE R EXTREMELY LIGHT (OR MORE LIKE NORMAL) AS SLOW AS I COULD FLY AND MAINTAIN CTL ABOUT 160 KTS. EMER LNDG MADE ABOUT 18 MINS AFTER ONSET AT SAN PEDRO SULA, HONDURAS. I HAD QUITE A LOT OF DIFFICULTY WITH ROLL CTL IN THAT FOR CORRECTIONS TO THE L WOULD TAKE A LOT OF PRESSURE (FOR ILLUSTRATION SAY 20 LBS) FOR CORRECTIONS TO THE R ALL I HAD TO DO WAS EASE OFF (FOR ILLUSTRATION SAY 2 OUNCES). FORTUNATELY, IT WAS A VERY CLR DAY AND SMOOTH. I FEEL IF I HAD THE NORMAL LOW LEVEL BUMPY AIR I WOULD HAVE POSSIBLY GOTTEN BEHIND THE CTL RESPONSE AND LOST CTL OF THE ACFT. THE COMPANY, BOEING, ETC ARE STILL IN SAN PEDRO SULA (NOW 3 DAYS AFTER THE INCIDENT) INSPECTING THE ACFT. IT HAS BEEN RELAYED TO ME THAT THEY HAVE BEEN ABLE TO DUPLICATE THE PROB ON THE GND, BUT DO NOT KNOW WHY. THE 'A' AUTOPLT PADDLES DISENGAGE BUT THE AUTOPLT ITSELF WILL NOT DISENGAGE UNTIL ALL PWR IS REMOVED FROM THE ACFT. THE YAW DAMPER IS EXCEEDING ITS DESIGN LIMITS ON ITS OWN INITIATIVE AND PUTTING INPUTS INTO THE SYS. AFTER THE FACT, IT APPEARS I WAS FIGHTING WITH THE AUTOPLT FOR CTL OF THE ACFT. THIS WAS A BOEING 737-300.

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.