Introduction
On Thursday, 2 June 1966, a Pilatus-Porter PC-6 aircraft registered as HB-FAO, owned and operated by the Swiss Federal Air Office, was involved in an accident on the Zanfleuron Glacier near the Sanetsch Pass. The aircraft was configured with skis and was being used for an official inspection flight of mountain and glacier airfields.
Flight Details
The pilot, born in 1918, held commercial pilot licenses with mountain and glacier landing endorsements. He had accumulated 4,313 flight hours on fixed-wing aircraft and 549 high-altitude landings. The aircraft carried two passengers: the pilot's son (born 1944) and an acquaintance (born 1925), who were assisting as support crew. The flight originated from Belpmoos Airport in Bern. Earlier that day, the pilot had performed two successful landings on the same glacier around 0912 hours. After a stop in Sitten and Montreux-Rennaz for administrative checks, the pilot departed Montreux-Rennaz at 1130 hours, heading back to the Zanfleuron Glacier.
Accident Sequence
At 1203 hours, the aircraft arrived over the glacier. The pilot could see the tracks from his earlier landings. After a 180-degree turn, he initiated an approach to the east-west landing direction with flaps set to 30°. Visibility was poor due to light haze despite sunshine. The pilot struggled to maintain visual contact with the landing tracks. During the final phase, just before flare, he lost sight of the tracks entirely. He began to flare and increased engine power, expecting ground contact. Instead, the aircraft dropped several meters, with the left wing dropping more. It struck the glacier with considerable sink rate, causing the left wingtip and landing gear (skis) to deform severely. The propeller struck deep snow and was torn off along with the reduction gear. The aircraft slid about 25–30 meters uphill and came to rest rotated about 90° to the left.
Damage and Injuries
All three occupants evacuated the wreckage uninjured. The aircraft sustained substantial damage, estimated at 30–40% of its value. It was noted that the aircraft was the second prototype of the Pilatus Porter PC-6 and differed from production models, raising questions about the economic feasibility of repair.
Discussion (from Source)
The accident occurred because the pilot lost adequate visual contact with the glacier surface. The approach may have been too low, causing the terrain's changing slope to obscure the earlier tracks. Conditions were extremely unfavorable due to high sun angle, haze, and fresh snow that lacked contrast, leading to a whiteout phenomenon. The pilot flared prematurely from too high an altitude, and the aircraft stalled and dropped. An approach slightly farther south (50–100 m) might have succeeded.
Probable Cause
The accident was attributed to the pilot flaring too high during a glacier landing under unfavorable visibility and lighting conditions, causing the aircraft to drop from several meters.