What happened
On July 1, 2001, a Pilatus PC-6/B2-H4, registration D-FALL, was performing a skydiving flight at Ravenna Airport. Shortly after takeoff, the aircraft experienced a sudden and violent pitch-up maneuver. The aircraft climbed to an altitude of approximately 20 meters before entering a stall. Despite the pilot's attempts to push the control column forward to level the aircraft, the plane could not be recovered and impacted the ground laterally to the runway on a grassy area.
The aircraft was carrying 11 people, including the pilot and 10 skydivers. All occupants managed to evacuate the aircraft on their own, though 5 persons sustained minor injuries. The aircraft sustained substantial damage, particularly to the nose, the left wing, and the landing gear, while the propeller was torn from the engine upon impact.
The investigation
The ANSV investigation focused on determining whether a mechanical failure, such as a trim runaway, or an operational error caused the sudden pitch-up. Investigators examined the wreckage, the electrical system, and the stabilizer trim mechanism. Technical tests confirmed that the electrical system and the trim system were fully functional at the time of the accident. The trim indicator was synchronized with the actual mechanical position of the stabilizer.
The investigation also considered the possibility of an accidental movement of the trim interrupt switch by a passenger seated near the center console. While not entirely ruled out, simulations suggested that such an accidental movement would have caused a gradual pitch change rather than the sudden movement observed. Investigators also reviewed the pilot's actions, noting that the pilot had performed 12 takeoffs and landings earlier that day, totaling approximately 8 hours of flight time.
Findings
- The primary cause of the accident was the loss of control due to an involuntary pitch-up moment immediately after liftoff, which led to a stall that could not be recovered due to the extremely low altitude.
- The investigation found that the most likely cause of the pitch-up was the improper stabilizer trim setting for the takeoff phase, specifically that the trim may have been left in a nose-up position used for landing.
- The aircraft's center of gravity was shifted rearward due to the weight of the 10 passengers, which increased the pitch-up tendency when the trim was incorrectly set.
- Human factors, including pilot fatigue from repetitive flight operations and the possibility of a missed checklist item due to the routine nature of the tasks, may have contributed to the incorrect trim setting.