Accident
On 17 June 2023 at 16:18 local time, a Cessna C172, registered as HB-CKU, departed from runway 34 of Buttwil airfield (LSZU) for a one-hour sightseeing flight with three passengers. Shortly after becoming airborne, the aircraft entered a steep nose-up attitude, stalled, and dropped to the left, striking the runway approximately 100 meters before the end of the runway. The aircraft sustained serious damage, but all four occupants were uninjured.
Aircraft and Pilot Information
The aircraft was a single-engine Cessna C172, owned and operated by Flugschule Eichenberger AG based in Buttwil. The pilot, a Swiss national born in 1996, held a Private Pilot Licence (PPL(A)) issued by the Federal Office of Civil Aviation under EASA. He had accumulated 70:22 total flight hours, with 3:59 hours in the preceding 90 days and 2:21 hours on the accident type (all within the last 90 days). The flight was conducted under visual flight rules (VFR) in private operation.
Circumstances
Weather conditions were good and summery with suitable VFR. The fuel tanks contained 121 liters, and the aircraft's mass and center of gravity were within limits. The flaps and elevator trim were set for takeoff, and the stall warning system was functional. Video footage confirmed the sequence of events. No technical defects or pilot impairments were identified.
The aircraft was equipped with an iPad mounted centrally on the instrument panel, programmed with navigation software for a route through Zurich's control zone via the mandatory reporting point 'Whiskey' located 5 nautical miles north of Buttwil. The iPad was found with a depleted battery. The pilot also used a headset with active noise cancellation.
Training Background
The pilot began airline transport pilot training in 2021 at Horizon Swiss Flight Academy. Basic PPL training, conducted on Cessna C152s at Flugschule Eichenberger in Buttwil, comprised 60:20 flight hours and 171 landings, ending with a successful flight test in September 2022. Training records showed a smooth progression with mostly positive instructor evaluations.
Familiarisation on the four-seat Cessna C172 occurred on an evening in April 2023, using the same instructor as for basic training. This familiarisation included 2:13 hours and 11 landings, featuring flights at maximum takeoff mass and solo flights. The instructor's checklist recommended regular landing practice without passengers. The pilot did not conduct any further C172 flights until the accident.
Investigation Findings
The investigation determined that the aircraft entered an aerodynamic stall shortly after lift-off. The stall was visually apparent from the aircraft's pitch attitude and audibly indicated by the stall warning. The pilot did not take corrective action by reducing elevator input, leading to the wing drop.
The STSB analysis considered that the pilot's failure to respond may have resulted from reduced perception due to possible distraction from the centrally mounted iPad and the noise-cancelling headset masking the aural stall warning. Additionally, the pilot's limited experience on the C172 type (only 2:21 hours) likely hindered recognition of abnormal flight conditions.
Regarding training, all instructional flights for the PPL and the C172 familiarisation were conducted with the same instructor, who consistently gave very positive evaluations. The pilot was unaware of any negative assessments contained in a final qualification document from Horizon Swiss Flight Academy. This may have affected the pilot's self-assessment of his skills.