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More than usual forward trim was required during and after takeoff. The auto pilot trim actuator ran out of forward trim and then ran continuously to full aft. The crew were unable to adequately manually trim forward. The aircraft returned for a normal descent and landing. The auto pilot mach trim actuator was found to be inoperative. The actuator had been fitted during overnight maintenance and the observed problem occurred on the first flight after installation. Ground test procedures after installation had not shown up any problems. Workshop rectification found anomalies with the backlash on the jackscrew and with the actuator length. The manufacturer advised that these anomalies would not have caused the problem that was experienced. The actuator was refitted four days after the workshop check and has since operated satisfactorily. The cause of the inflight problem was not discovered.
Download Final Report
[ Download PDF: 11KB]
General details
Date: 29 May 1994 Investigation status: Completed 
Time: 10:15 EST  
 Investigation type: Occurrence Investigation 
 Occurrence type: Flight control systems 
Release date: 29 August 1994 Occurrence class: Technical 
Report status: Final Occurrence category: Incident 
Aircraft details
Aircraft manufacturer: The Boeing Company 
Aircraft model: 737-377 
Aircraft registration: VH-CZP 
Sector: Jet 
Damage to aircraft: Nil 
Departure point:Melbourne Vic
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Last update 21 October 2014