What happened
On February 18, 2021, a Piper PA3-200T «Seneca II», registration T7-RAR, was conducting a private instrument flight from Locarno to St. Gallen-Altenrhein. The pilot intended to perform a Required Navigation Performance (RNP) approach for training purposes, despite knowing that dense fog was covering the area with visibility significantly below landing minimums.
During the approach, the pilot was cleared to descend and intercept the final approach course. While the aircraft was descending, the pilot focused on the glidepath indicator on the electronic flight instrument system. As the aircraft descended through the fog layer, the pilot unexpectedly encountered the water surface. The pilot attempted to pull up, but the aircraft struck the surface of Lake Constance, causing the right main landing gear to break away. The aircraft subsequently sank to a depth of approximately 90 meters.
The pilot managed to exit the aircraft and clung to the detached landing gear leg, which remained floating on the surface. Despite the freezing 5°C water temperature, the pilot was discovered by a fisherman approximately one hour later and rescued from a state of severe hypothermia.
The investigation
An investigation by the Swiss Transportation Safety Investigation Board (SUST) examined the flight profiles, meteorological conditions, and the aircraft's avionics. Radar data showed the aircraft was descending at a rate of approximately 1,250 feet per minute. The investigation also utilized a flight simulator to attempt to replicate the pilot's claim that the glidepath indicator showed the aircraft was well above the path throughout the descent. However, investigators were unable to reproduce this specific instrument error.
Findings
- The pilot experienced target fascination, becoming so fixated on the glidepath indicator that situational awareness regarding the actual progress of the approach was lost.
- The pilot failed to observe the Decision Altitude (DA), which requires an immediate missed approach if visual references are not met.
- The pilot performed the descent manually and did not cross-check other flight instruments.
- The transition into the fog layer likely caused the pilot to lose track of the glidepath indicator's movement from bottom to top, leading to a misinterpretation of the aircraft's vertical position.