What happened
On July 23, 2013, a Piper PA-28-161, registration HB-PNR, was conducting a VFR instructional flight at Kägiswil airfield. The flight, which included a flight instructor, a student pilot, and a passenger, was intended to be a short 45-minute session. Despite the presence of nearby thunderstorm activity, the flight proceeded, with the instructor intending to monitor the weather and return early if necessary.
During the approach to runway 21, the aircraft encountered intense turbulence and heavy rain. The aircraft drifted off the runway centerline due to strong winds, prompting the crew to initiate a go-around. While attempting to execute a left turn to reposition for another approach, the aircraft was caught in severe atmospheric instability. At an altitude of approximately 50 meters, the aircraft lost control, developed a steep bank angle, struck a tree, and impacted the ground near Feldwiden. The accident resulted in two fatalities among the crew and one fatality among the passenger.
The investigation
SUST examined radar data, radio communications, and meteorological records from the region. The investigation focused on the wind conditions at the time of the accident, noting that significant wind gusts of up/to 32 knots had been recorded in the area shortly before the impact. Investigators also reviewed the flight history and the decision-making process regarding the approaching storm cells. Technical inspections of the Piper PA-28-161 revealed no pre-existing mechanical failures that contributed to the crash.
Findings
- The primary cause of the accident was the loss of control at low altitude during a go-around following encounter with severe turbulence.
- The crew underestimated the rapid development and increasing intensity of the thunderstorm activity.
- Severe wind shear and gusty conditions, likely associated with a microburst or outflow from the storm, made a stabilized approach impossible.
- The aircraft was subjected to extreme environmental forces, including heavy precipitation and rapidly changing wind directions, which left the crew with almost no operational options during the maneuver.