What happened
On December 25, 1975, a Maule M-4-210, registration HB-ETN, was conducting a private sightseeing flight from Samedan via Davos. While navigating the Val Susauna toward the Scaletta Pass, the pilot encountered Föhn conditions, which made maintaining altitude difficult. As the aircraft approached the pass, the left side of the valley became obscured by clouds.
Due to the lack of visibility on the left, the pilot attempted a right-hand turn. However, during this maneuver, the aircraft encountered significant downward air currents caused by Föhn turbulence. This loss of altitude prevented the aircraft from clearing terrain approximately 2,700 meters high, forcing the pilot to abort the turn at roughly a 90-degree angle toward the Scalettahorn. Shortly after, the aircraft entered clouds near the start of the Scaletta Glacier. In an attempt to regain visibility, the pilot reduced power and speed to approximately 70-80 mph. Without visual reference, the aircraft struck the glacier with its landing gear and left wingtip.
The investigation
The investigation established that the pilot held a valid license, including qualifications for mountain landings, and had no known health issues relevant to the accident. The Maule M-4-210 was airworthy, with its weight and center of gravity within permissible limits. Meteorological data confirmed that the area was experiencing strong NW-N winds with gusts up to 50 knots, driven by a significant pressure difference between the north and south sides of the Alps. This pressure gradient caused severe downdrafts, particularly on the southern slopes of the mountain ranges.
Findings
- The pilot entered an area where a safe turnaround was no longer possible due to the combination of topography and meteorology.
- Severe Föhn-induced turbulence caused a loss of altitude during the turning maneuver.
- Visibility was extremely limited, with visibility within clouds dropping to between 50 and 100 meters.
- The decision to execute the turn was made too late to avoid the hazardous conditions.