What happened
On January 8, 2016, at approximately 10:10 local time, an SA 315 B helicopter, registration HB-XII, was conducting a training flight at Raron (LSTA). The flight was intended to practice autorotations. The first portion of the mission focused on standard autorotations, while the second phase aimed to practice initiating an autorotation from a hover by reducing engine power.
Following a demonstration of the maneuver by the flight instructor, the student pilot took control of the aircraft. The helicopter was hovering roughly half a meter above the ground. To reduce power in this specific aircraft model, a manual adjustment of the power lever is required. During the procedure, the instructor prepared to adjust the lever while the student pilot responded to a countdown. In an attempt to initiate the maneuver, the student pilot rapidly lowered the collective. This sudden movement caused the helicopter to strike the ground with significant force, resulting in a hard landing.
The investigation
The investigation focused on the sequence of control inputs during the transition from a hover to a simulated autorotation. Investigators examined the mechanical requirements of the SA 315 B power lever, noting that the instructor had to use his right hand to manipulate the lever while being prepared to assist with the cyclic control. The investigation established that the student pilot's rapid lowering of the collective was the direct cause of the impact.
Findings
- The primary cause of the incident was the student pilot's improper application of the collective control during a hover-based autorotation maneuver.
- There was a discrepancy in required technique: while initiating an autorotation in flight requires an immediate and full lowering of the collective, an autorotation initiated from a hover requires the pilot to pull the collective to ensure a controlled descent.
- It is highly probable that the student pilot performed a reflexive action learned during the earlier, high-altitude autorotation training, applying the same rapid downward collective movement used in flight to a situation where a controlled pull was necessary.