What happened
On August 4, 2018, a Socata TB10, registration HB-EZW, departed from Kägiswil airport for a private flight toward Basel. The aircraft was carrying a pilot and three passengers. After taking off, the aircraft entered a continuous climb, initially following a route toward the Alpnachersee before turning north toward the Rengg Pass ridge.
As the aircraft approached the ridge, it maintained a low ground speed of approximately 70 knots. At 09:50, the aircraft struck treetops at the northern end of the Schoffeldes ridge at an altitude of roughly 900 meters. The impact severed parts of the right wing's trailing edge, sending the aircraft into a steep, uncontrolled spiral dive. The aircraft subsequently struck the forest floor on the north slope of Schattenberg, where it caught fire. All four occupants were killed in the crash.
The investigation
SUST investigators examined the flight path, aircraft technical condition, and pilot experience. The investigation utilized 3D modeling and laser scanning of the crash site to reconstruct the aircraft's flight attitude. Technical analysis confirmed that the aircraft was within weight and balance limits and showed no signs of mechanical or structural failure prior to the collision. The pilot, who held a Commercial Pilot License, had extensive experience in high-performance turbine aircraft but had not flown this specific model type in the 90 days preceding the accident.
Findings
- The pilot utilized a risky flight tactic by approaching the ridge at a low speed and a blunt angle during a climb.
- The low airspeed required a high pitch attitude, which significantly restricted the pilot's forward visibility; modeling showed the ridge was barely visible in the final 30 seconds before impact.
- A lack of recent training on this specific aircraft type contributed to the accident, as the pilot struggled to anticipate the rapid changes in flight vector characteristic of this light aircraft.
- The aircraft was operating at a reduced power setting, which limited the climb performance compared to maximum available power.