What happened
On March 23, 1997, at approximately 11:30 local time, a Jodel D 140R aircraft with registration HB-SFG was involved in an accident during a mountain landing examination flight. The flight originated from Ecuvillens aerodrome, carrying an expert pilot and a candidate pilot. After successfully conducting reconnaissance and four precise landings on the Tsanfleuron glacier under acceptable visibility conditions, the crew proceeded to evaluate other sites.
The decision was made to skip the Wildhorn site due to downdrafts and poor ground visibility. Following a successful reconnaissance of the Petersgrat south area, the pilot attempted landings at Kanderfirn/Mutthorn, where another training aircraft was also present. To complete the examination, the expert directed the candidate to approach the newly vacated Petersgrat north site.
During the final approach to Petersgrat north, the left ski struck the glacier surface hard. The crew immediately applied full power, allowing the aircraft to land briefly higher up the slope before turning left and taking off again. Upon becoming airborne, the pilot reported that the left ski was in a vertical position. The expert took control and noticed a negative variometer indication. Initially intending to follow the glacier slope toward Kandersteg, the expert changed course due to diffuse lighting conditions and lack of visual references in the basin. During a left turn to face the slope, the wingtip struck the snow, causing the aircraft to crash.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the technical condition of the aircraft and the operational circumstances. The aircraft was airworthy for VFR day operations, having passed its 50-hour inspection on March 20, 1997. Post-accident inspection revealed two major cracks on the upper part of the left ski and a broken rear return cable, which had been new only two months prior. The ELT did not activate, but the seatbelts held.
Weather data from Zurich indicated dry conditions with overcast skies (6-8/8 Cs/As at 7000ft), visibility over 40 km, and weak winds. However, on the glacier itself, the sky was covered, creating diffuse light without clear shadows or ground traces. The pilot had 11,973 total flight hours, while the candidate had 1,203 hours.
Findings
The accident was caused by repeated misjudgment of the terrain in diffuse lighting conditions. The initial hard contact with the left ski likely broke the rear cable due to excessive force from the glacier's slope. While the crew recovered control after this first impact, the expert pilot made critical errors during the subsequent maneuver. He relied on a variometer that had a delayed response time, interpreting it as a descent when the aircraft was actually climbing or level. Combined with the lack of visual references in the basin, he attempted a left turn to return to his track, which led to the wingtip striking the snow.
Safety action
The investigation highlighted the risks of relying on instrument indications with known delays during critical low-altitude maneuvers in featureless terrain. It also underscored the importance of recognizing when visual conditions are insufficient for safe mountain flying, regardless of overall visibility ranges.