Serious incident to the Pilatus PC6 registered F-GEBS on 23/03/2025 at Saint-Etienne Loire

During the annual or 100-hour inspection, in order to inspect a structural frame, the elevator trim actuator and the associated lower connecting piece were removed by the maintenance workshop mechanic according to the AMM job card.

At the end of this inspection during which no anomaly was identified, the mechanic attached the connecting piece to the frame without realising that he had positioned it in the wrong direction. The elevator trim actuator was then attached to the connecting piece. As it is a hinged connection and the actuator is movable, it was possible to position the actuator on the connecting piece.

This task was not considered a critical task and did not give rise to a specific check and the operation was validated as it was. On completion of all the maintenance operations, the aeroplane resumed flights.

In the following seven flight hours, the aerodynamic loads applied to the tail plane were transmitted to frame FR12A in an adverse stress mode linked to the non-compliant installation of the connecting piece of the trim actuator and made it possible for the frame to collapse.

During the incident flight, while descending with the elevator trim set to "full nose down”, the frame tore in several places, causing the elevator trim actuator to collapse. This collapse modified the setting of the variable incidence horizontal stabilizer and jammed the elevator trim control, which was felt by the pilot.

The pilot's actions (increasing power and extending the flaps) allowed him to regain limited but sufficient control of the aeroplane to make a precautionary landing at a nearby aerodrome.