Introduction
On 23 July 2013 at approximately 17:25 local time, a Piper PA-28-161, registered HB-PNR, crashed at Feldwiden, near Kägiswil Airfield (LSPG), in the municipality of Sarnen, Obwalden, Switzerland. The aircraft was operated by Flugbetriebs AG Sarnen-Kägiswil and was on a VFR training flight serving as an introductory flight.
Flight History
The flight was crewed by a flight instructor (Swiss citizen, born 1946, holding a CPL(A) with SEP and FI ratings, approximately 4245 total flight hours, of which about 1000 on type) and a student pilot (Swiss citizen, born 1992, with 9 hours and 47 minutes total flight time, all on type). A passenger, the student's godfather, was also on board. The aircraft had been refueled earlier that day and carried 24 US gallons of fuel at departure.
Pre-flight discussions included the presence of thunderstorms over the Entlebuch region. The instructor stated he would monitor the weather and was inclined to return early if necessary. The student's father noted the availability of alternate airfields. The instructor remarked that on previous days, similar thunderstorms had dissipated prematurely.
The flight departed Kägiswil runway 03 at 16:58 local time. After departure, the aircraft proceeded toward Luzern, climbing to 4500 ft QNH, performed several turns, and then turned back toward Kägiswil. Radar data showed the aircraft descending east of Alpnach at 17:16:24.
Meanwhile, another instructor flying a similar aircraft, HB-PNG, experienced a severe gust at 17:05 while turning base for runway 03. He took control and landed with a strong tailwind. After landing, he observed HB-PNR approaching from the Lopper area and at approximately 17:20 radioed his colleague that landing on runway 03 was not possible due to the wind situation.
Accident Sequence
HB-PNR conducted a go-around at low altitude. During the go-around, the aircraft lost control in the presence of strong turbulence and collided with terrain at an elevation of 469 meters above mean sea level.
Injuries and Damage
All three occupants—the flight instructor, student, and passenger—sustained fatal injuries. The aircraft was destroyed. Minor field damage occurred.
Cause
The accident was caused by collision with terrain following loss of control at low height after a go-around in the presence of strong turbulence. The underestimation of the development of thunderstorm activity and its intensity played a role in the accident.