What happened
On May 1, 1997, a private helicopter flight involving five passengers departed Zurich for a scenic tour with a landing at the Jungfraujot mountain landing site. The pilot had performed weight and balance calculations prior to departure, intending to land on a fresh snow track left by a snow groomer.
During the final approach, the pilot maintained a slow forward speed. As the aircraft approached the landing zone, the rotor wash disturbed the deep, fresh snow, creating a cloud of powder that enveloped the rear of the aircraft. This triggered a whiteout effect, causing the pilot to lose all ground visual references. In an attempt to recover, the pilot initiated a go-around with a right-hand turn. However, approximately 100 meters from the point of the aborted landing, the aircraft struck rising terrain amidst the snow cloud. The main rotor blades struck the fresh snow, causing the helicopter to flip onto its roof.
The investigation
Investigators examined the aircraft's performance data and the pilot's preparations. While the pilot had conducted thorough pre-flight planning, the investigation found that the actual weight of the aircraft exceeded the planned weight. The pilot had used optimistic estimates for passenger and baggage weights, and the aircraft was heavier by approximately 75 kg due to additional fuel.
Furthermore, the investigation noted that while the pilot had checked weather conditions via telephone, the specific depth of the recent snowfall (80 to 100 cm) was not discussed. The investigation also reviewed the aircraft's technical state, finding it well-maintained, and examined the pilot's experience, noting he held a valid mountain landing rating but had limited experience landing in such significant fresh snow depths.
Findings
- The pilot underestimated the danger of swirling snow during a slow approach, which led to the loss of visual ground references.
- The decision to initiate a go-around was made too late to avoid the terrain.
- The aircraft lacked the necessary power reserve (HOGE performance) required to safely execute an aborted landing.
- There was a significant discrepancy between the pre-flight performance planning and the actual weight of the aircraft during the flight.
Safety action
- The Federal Office of Civil Aviation (FOCA) was advised to produce instructional video material demonstrating the whiteout effect.
- The investigation recommended that FOCA review the required power reserves for mountain landings for both private and professional pilots.
- It was suggested that safety directives regarding mountain landing performance should be communicated to all pilots holding mountain landing ratings, rather than being limited to flight schools and instructors.