What happened
On September 9, 1964, a professional helicopter pilot was conducting material transport operations for the Mattmark dam construction project in the Almagellertal valley. Operating an Agusta Bell 204 B, registration HB-XBN, the pilot was performing the final flight of the day, moving cargo from the Almagellerbach construction site back to Saas Almandell.
At approximately 15:50, instead of following the established flight path used during previous successful legs of the mission, the pilot descended directly into the axis of the valley. During this descent, the aircraft struck a cable belonging to an auxiliary industrial cableway. The impact caused the helicopter to crash and subsequently catch fire. The pilot sustained fatal injuries, and the aircraft was destroyed.
The investigation
The investigation examined the aircraft's technical condition, the pilot's medical history, and the environmental factors at the time of the accident. Technical inspections of the wreckage found no evidence of mechanical failure; notably, the pilot did not attempt an autorotation, which is the standard procedure for a pilot encountering engine trouble.
Investigators also reviewed the pilot's recent activity and physical state. While the weather was clear with light winds, the investigation focused on the pilot's health. Evidence showed the pilot had been working a heavy schedule and had reported stomach discomfort earlier that day. Medical experts reviewed the pilot's recent medical examinations and the circumstances surrounding his last meal.
Findings
Technical analysis ruled out any mechanical or engine failure as a cause for the collision. The investigation established that the pilot was aware of the presence of the cables in the valley, as they had been identified during a reconnaissance flight earlier that day.
However, the investigation found that the pilot had consumed a heavy, indigestible meal consisting of sauerkraut, dessert, and multiple soft drinks while already suffering from gastric distress. The investigators concluded that a sudden medical malaise likely occurred, which temporarily incapacitated the pilot or severely diminished his ability to maintain situational awareness, leading to the fatal deviation from the safe flight path.