Background
On the morning of 7 August 1973, a SA 315 B Lama helicopter, registration HB-XDX, operated by Air Zermatt AG, was tasked with transporting stacked cast iron pipes from Rittine to a ridge above "Hellene" near St. Niklaus, Switzerland. The pipes were 6 m long, 10 cm in diameter, and coated with tar. Load bundles of 680 kg each were prepared.
Accident Sequence
For the first three flights, the load was secured using two 8 m endless nylon slings attached to the cargo hook, causing the load to hang horizontally. For subsequent loads, only 6 m slings were available. A mechanic improvised by threading a third 6 m sling through the free ends of two others. During the first attempt to lift a bundle secured this way, one sling slid toward the center of the pipes. The pilot observed this in the mirror, set the load down, and released it. No further action was taken.
Shortly after 0845 hours, the pilot lifted another bundle with the same improvised rigging. The load tilted approximately 10–20° from horizontal. After flying about 1 km, the load suddenly slipped from the slings and fell. Simultaneously, the helicopter began to rotate rapidly, and witnesses saw it enter a wooded slope. The accident occurred at 0846 hours at coordinates 629 340/114 800, elevation 1315 m.
Wreckage and Injuries
The helicopter was destroyed. The pilot sustained fatal injuries. No other individuals were involved. The debris field measured approximately 300 m by 150 m. The main wreckage lay inverted at the lower end. A 6 m nylon sling was found wrapped around the tail rotor gearbox, which had separated in flight. The tail rotor shaft was broken about 10 cm from the coupling. Personal effects and a fire extinguisher were found 300 m from the wreck, likely ejected due to rotation of the cabin.
Investigation Findings
The investigation reconstructed the two sling configurations. The improvised method using three 6 m slings produced nearly double the horizontal tension compared to the method with two longer slings, increasing the risk of slippage. The first warning sign—the sling sliding during the initial lift—was not resolved. There was no functional radio between pilot and ground crew; it had been removed two days prior due to a technical issue. The pilot likely did not have time to jettison the load via the electric or mechanical release due to the rapid onset of rotation at low altitude (approx. 130 m above ground).
Probable Cause
Loss of controllability due to severe damage to the helicopter caused by improperly secured load.