History of the Flight
On Sunday 23 March 2025, a Pilatus PC6 B2H2, registered F-GEBS, was conducting a skydiving flight. The pilot took off from Saint-Galmier aerodrome at around 09:20 local time. After the skydivers had jumped, the pilot initiated a descent to join the base leg for runway 16. While descending through 4,000 ft, he felt a point of friction on the control column and observed that the elevator trim was jammed in the full nose-down position. By applying substantial force and increasing turbine power, he stopped the descent and held level flight. He then explored configurations of speed, power, and flap deflection to manage vertical profile. He informed the Clermont-Ferrand controller of the control problem and stated his intention to divert to Saint-Etienne Loire aerodrome, which had a longer paved runway. He landed on runway 17 without further issues and taxied to parking.
Aircraft and Pilot Information
The aircraft was a Pilatus PC6 B2H2 with a Pratt & Whitney PT6A-34 engine, configured for skydiving and equipped with a manual elevator trim control. It had logged approximately 25,530 flight hours. The pilot held an ATPL(A) and a PC6 type rating, with 8,800 total flight hours, including 4,720 on the PC6. The aeroplane sustained slight damage.
Examination and Findings
Post-incident examination focused on the tail section, specifically the elevator trim actuator and frame FR12A. Tests on the ground showed that the trim control handle moved freely, but the actuator rod movement caused deformation of the frame wall. The actuator was found incorrectly fastened, having moved forward and downward due to torn frame attachments. The lower connecting piece of the trim actuator had been installed in the wrong direction, leading to out-of-plane loads that exceeded the frame's mechanical strength, causing deformation and tearing.
Maintenance History
The aircraft had undergone a 100-hour/ annual inspection between 9 December 2024 and 4 February 2025 at a Part-145 workshop, after which it had flown seven hours. The maintenance included inspection of frame FR12A, requiring disassembly and reassembly of the connecting piece. This task was not classified as critical and was not subject to a specific check. The applicable maintenance manual (AMM 53-30-00) did not specify the installation direction or warn of potential inversion.
Conclusions
The investigation concluded that during the inspection, the mechanic reinstalled the connecting piece in the wrong orientation. The incorrect assembly introduced unintended stress, causing the frame to collapse under aerodynamic loads during the incident flight. The pilot's actions, including increasing power and extending flaps, allowed him to regain sufficient control for a precautionary landing.
Contributing factors included maintenance documentation lacking a warning about possible incorrect positioning, and the task not being identified as critical, thus not requiring a specific check. Following the incident, the maintenance workshop amended the job card to illustrate correct installation and added the task to the critical list.