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The control difficulties experienced by the crew shortly after departure could be attributed directly to the horizontal trim system operating in the reverse travel sense to that commanded by the pilot in command’s (PIC) inputs to the horizontal stabilizer trim switches.

The investigation determined that systemic failures present during maintenance allowed the aircraft to be returned to service with a horizontal stabiliser trim system that operated in the reverse sense. Further, this incorrect flight control function was not detected during the pre-flight inspection by the flight crew.

A task that was maintenance intensive and/or extended over several shift periods involving numerous personnel required careful management in the co-ordination of effort to ensure every requirement was addressed to safely return the aircraft to an airworthy condition. In this incident there was a breakdown in this defence through absent or poorly defined handover procedures, documentation and co-ordination of the maintenance.

Disturbance of a flight control system during maintenance triggers the requirement for an additional layer of defence in the duplicate inspection procedure. In this incident the engineers were unsure of when the procedure was to be employed and this lead to a breakdown of the defence. A clearly defined procedure in the company maintenance control manual for invoking the duplicate inspection would have ensured a duplicate inspection was prescribed, which in turn should have identified the trim reversal prior to the aircraft’s release to service.

The aircraft provided the crew with an aural alert system with a known difference from its fleet siblings. The perception by the pilot in command (PIC) of the aircraft being inherently different, combined with a loading distraction at the critical trim function check time in the pre-flight sequence, probably led to a misinterpretation by the PIC of his response to the anomaly.

Once airborne and with the emergency in progress, the PIC established that he had control, but neglected to consider selection of the trim system control to the copilot’s control wheel as an option. This may have been as a result of his decision not to manipulate the trim system any further due to possible mechanical failure.

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