Aircraft and Operator
- Type: SA 315B Lama
- Registration: HB-XEV
- Operator: Air Zermatt AG, Zermatt
- Total Time: 2381 hours
- Last periodic check: 17 November 1977 (1740 hours)
- Last 100-hour check: 25 October 1978 (2305 hours)
- Valid certificates of airworthiness and circulation.
Pilot Information
- Born: 1938
- License: Professional pilot (helicopters)
- Total flight hours: 4015
- Hours on type: approximately 800
- Hours in last 90 days: 125
Flight Details
- Date and Time: 16 November 1978, 1626 hours local time (GMT+1)
- Location: Zermatt, Valais, Switzerland (coordinates 622.700 / 093.350)
- Altitude: 2000 m
- Phase: Cruise
- Operation: Commercial
Narrative
Earlier that day, the pilot had conducted multiple transport flights in the Zermatt area between Trockener Steg (2940 m) and Petit Cervin (3800 m). In the late afternoon, after landing at Trockener Steg with an empty drum suspended on a sling, the pilot held a hover to facilitate hooking a transport net containing ropes and nets, then landed to allow his mechanic and two restaurant employees to board. After takeoff, the pilot descended toward the valley following the slope. While passing the ridge above the lower part of the Gorner glacier, at a place called "Gerwetsch", he realized he had too much speed and pulled back on the cyclic to slow down. As he returned the cyclic forward to resume a normal attitude, accompanied by a sudden increase in descent rate, he heard two cracking sounds from the rear. He lost pedal control, initially suspecting a tail rotor drive failure. He considered a forced landing south of Zermatt but was reminded of cable car cables. He then thought of heading to the Gorner glacier but deemed it too hazardous due to numerous seracs. Suddenly, the helicopter began to spin, slowly at first then faster. Disoriented and instinctively avoiding the ground, the pilot pulled up on the collective. The helicopter impacted an uneven rocky slope, overturned, and came to rest on its left side about 40 meters below. All four occupants were injured and were quickly rescued and taken to the hospital in Viège by the operator, who had been informed by radio.
Established Facts
- The loss of yaw control was caused by the rupture of the tail rotor blades after the external load, suspended on a 6-meter sling, penetrated the tail rotor disc. The blades were torn off at the root and not found; they tore the net and ingested part of its contents, found wrapped around the hub.
- The turbine operated until impact; no fire occurred; the fuel tank (containing about 110 liters of kerosene) remained intact; the fuel shutoff valve was not activated.
- Weight and center of gravity were within limits.
- The load (ropes and nets) weighed 68 kg.
- A mirror outside the cabin allowed the pilot to monitor the load.
- The pilot held valid licenses and qualifications. On the accident day, he had flown 51 rotations (49 between Trockener Steg and Petit Cervin) totaling 5:22 hours. He had flown 6:03 hours the day before and 13 minutes two days before. Over the last half-month, he flew 28:13 hours; over the last two half-months, 42:22 hours; over the last year, 470 hours.
- The pilot stated he had a moment of inattention and forgot about the load on the sling.
- Weather played no role: mostly clear, good visibility, light and variable wind; freezing level at 1400 m.
Cause
- The accident is due to the pilot performing a maneuver incompatible with the nature of the load he was carrying.