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.
Synopsis
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.
NASA callback
The reporter stated that this aircraft has had at least two similar un-commanded rudder events which resulted in significant maintenance effort attempting to fix the problem. Following this event; the yaw dampener wiring was changed. The company Mechanic riding in the aircraft's aft seating during this event reported the loud banging and become very frightened about the aircraft's integrity because of the amount of empennage movement. A Flight Attendant on board stated that on a previous similar event with this aircraft she had to sit down on the aft galley floor to prevent being injured. The reporter stated that other pilots have accepted the aircraft because of Company intimidation and also some events have been less severe.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.