What happened
On August 7, 1973, an SA 315 B Lama, registration HB-XDX, was performing a commercial transport mission near St. Niklaus, Switzerland. The mission involved transporting heavy bundles of tarred cast-iron pipes from a loading site at 1,465 meters to a drop site at 1,600 meters altitude.
During the second transport flight of the morning, the cargo—consisting of 6-meter-long pipes weighing approximately 680 kg—began to tilt at an angle of 10 to 20 degrees. Shortly after takeoff, the load slipped from its slings. A loose nylon sling became entangled in the tail rotor, causing the aircraft to lose control and enter a rapid rotation. The helicopter subsequently struck a wooded slope at an altitude of approximately 130 meters. The pilot was killed in the crash, and the aircraft was destroyed.
The investigation
Investigators examined the wreckage and reconstructed the sling configuration used for the load. They found that because the necessary 8-meter slings were unavailable, the ground crew had improvised by using three 6-meter slings, threading one through the ends of the others.
Technical analysis revealed that this specific arrangement created significantly higher horizontal tension compared to the standard method. The investigation also noted that the pilot had previously aborted a lift using this same improvised method because a sling had slipped toward the center of the pipes, yet the pilot proceeded with the second flight without addressing the underlying issue with the ground crew. Furthermore, the investigation established that the aircraft's radio had been removed for repairs two days prior, preventing the ground crew from warning the pilot of the shifting load.
Findings
- The primary cause of the accident was the loss of controllability due to severe damage caused by an improperly secured load.
- The improvised sling arrangement was inherently unstable; the lack of lateral security allowed the slings to slide toward the center of the pipes, causing the load to slip.
- The entanglement of a loose sling in the tail rotor caused the tail rotor to fail and led to the partial separation of the rear fuselage.
- The pilot's ability to react was severely limited by the low altitude and the extreme centrifugal forces generated during the aircraft's rapid rotation.
- The absence of radio communication prevented the ground crew from alerting the pilot to the visible instability of the cargo.