While on final approach to Brisbane at about 1,000 ft, the crew
of the Boeing 737 reported feeling a 'kick' in the rudder pedals
accompanied by a minor aircraft yaw oscillation. It was reported
that there was no aircraft ahead to cause wake turbulence.
Investigation by the aircraft operator suggested a problem with
the rudder power control unit. The aircraft manufacturer
recommended that the standby rudder actuator and the standby input
rod bearings should also be examined for wear; no wear was
evident.
The rudder power control unit had accumulated 3,064 hours since
its overhaul by the manufacturer in May 1999. It was removed from
the aircraft and forwarded to the USA for examination.
The examination was conducted by the component manufacturer and
supervised by the National Transportation Safety Board of the USA
on behalf of the Australian Transport Safety Bureau. No
discrepancies that may have led to the anomaly in the operation of
the rudder power control unit were found. The internal and external
components contained no evidence of excessive wear, damage or
overtravel and met the manufacturer's standards for in-service
units.
In support of the investigation, the National Transportation
Safety Board also conducted a performance simulation study based on
the actual aircraft configuration data at the time of the incident.
The study concluded that the rudder had oscillated.
The investigation was unable to determine why the rudder
reportedly oscillated.