Turbulence event, Adelaide Airport, South Australia, on 15 December 2006, Boeing 737-476, VH-TJH

At approximately 1416 Central Daylight-saving Time on 15 Dec 2006, the flight crew commenced a take-off roll in a Boeing Company 737-400 aircraft, registered VH-TJH, on a scheduled passenger service from Adelaide, SA to Melbourne, Vic.

At a speed of approximately 50 kts, the crew reported an abrupt, uncommanded left yaw. Corrective action was applied, and the take-off was continued without further incident. The remaining flight was uneventful.

The flight crew subsequently reported that they did not notice any rudder pedal movement coincident with the uncommanded yaw and recalled that there was a gusting crosswind from the left during the take-off.

Data from the aircraft's Flight Data Recorder was recovered and downloaded by the Australian Transport Safety Bureau (ATSB) for review. That review indicated that the input to the aircraft rudder was not uncommanded and that the rudder pedals moved proportionally to the rudder surface deflection at all times. An examination of the aircraft by the aircraft operators' maintenance engineers did not identify any reason for the uncommanded yaw and the aircraft was released back to service. Additionally, there was no other aircraft traffic in the vicinity that may have generated wake turbulence in the immediate timeframe prior to the take-off.

While the nature of the uncommanded yaw could not be positively identified, it is likely that the event was related to an atmospheric disturbance or turbulence during the take-off.

The ATSB continues to monitor such reported uncommanded yaw events and has reported similar events in the past (see occurrence reports 200700035, 200500994 and 199703237 available on the ATSB website).