Narrative:

At 35;000 ft; approximate speed mach .78; with center autopilot; LNAV; and VNAV selected a rapid and un-commanded left/right yaw movement occurred for approximately 3 seconds. No EICAS messages or warning lights or indications on status page; or rudder pedal movement indicated shortly before; during; or several minutes after the event. No turbulence of any type was indicated before; during; or several minutes after the event. The only turbulence encountered during the flight was when the aircraft was in range of returning to its departure airport. Company maintenance control was contacted shortly after the event via phone patch. A description of the event was communicated to them. Company maintenance requested and deemed the aircraft safe to return to the departure airport. The crew onboard the aircraft agreed to comply with company's request since the aircraft was flying normal after the event. The aircraft returned to the departure airport in a normal and safe manner. After the flight was completed; after the aircraft un-commanded yaw logbook entry was made in the aircraft logbook and the logbook was no longer in the possession of the pilots; a company mechanic sitting in the back of the aircraft during the flight stated that when the event happened he also heard several loud banging noises coming from the ceiling in the rudder area of the aircraft. The loud banging noises happened during the un-commanded yaw motion and sounded like the rudder hitting its stops. To my knowledge it cannot be verified if this additional information was relayed to the mechanics working on the un-commanded yaw aircraft.

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Original NASA ASRS Text

Title: A B767-300 experienced a rapid; uncommanded three second left to right rudder deflection which was heard and felt by a Mechanic in the cabin. The aircraft was returned to the departure airport.

Narrative: At 35;000 FT; approximate speed mach .78; with center autopilot; LNAV; and VNAV selected a rapid and un-commanded left/right yaw movement occurred for approximately 3 seconds. No EICAS messages or warning lights or indications on status page; or rudder pedal movement indicated shortly before; during; or several minutes after the event. No turbulence of any type was indicated before; during; or several minutes after the event. The only turbulence encountered during the flight was when the aircraft was in range of returning to its departure airport. Company Maintenance Control was contacted shortly after the event via phone patch. A description of the event was communicated to them. Company Maintenance requested and deemed the aircraft safe to return to the departure airport. The crew onboard the aircraft agreed to comply with Company's request since the aircraft was flying normal after the event. The aircraft returned to the departure airport in a normal and safe manner. After the flight was completed; after the aircraft un-commanded yaw logbook entry was made in the aircraft logbook and the logbook was no longer in the possession of the pilots; a company Mechanic sitting in the back of the aircraft during the flight stated that when the event happened he also heard several loud banging noises coming from the ceiling in the rudder area of the aircraft. The loud banging noises happened during the un-commanded yaw motion and sounded like the rudder hitting its stops. To my knowledge it cannot be verified if this additional information was relayed to the mechanics working on the un-commanded yaw aircraft.

Data retrieved from NASA's ASRS site as of April 2012 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.