What happened
During a type conversion training flight near Lanseria Aerodrome, a Bell 206L-4 helicopter, registration ZS-RHZ, experienced a significant rotor strike upon landing. The flight, which involved an instructor and a student pilot, was conducting maneuvers in the general flying area when the crew entered into an autorotation from an easterly direction.
As the aircraft approached the ground, the instructor noted that the nose of the helicopter remained too high following the flare. This resulted in a hard landing where the rear skids made firm contact with the terrain, causing the aircraft to skid for approximately one meter. During this impact, the low rotational speed of the main rotor caused the blades to flap downward, striking the left-hand vertical fin stabilizer and the tail boom.
The investigation
The SACAA AIID investigation examined the flight parameters, maintenance history, and environmental conditions. The investigation confirmed that the weather was clear with good visibility and a 12-knot wind. The aircraft's maintenance records showed that the Bell 206L-4 had undergone a mandatory periodic inspection only ten hours prior to the incident, and the maintenance organization had been recently audited with no major findings. The investigation also noted that the aircraft was not equipped with a cockpit voice recorder or flight data recorder, as they were not required for this type.
Findings
- The instructor allowed the main rotor RPM to decay below the minimum required level during the final stages of the autorotation.
- This decay in RPM led to an increased sink rate and a hard landing.
- The low rotor speed caused the blades to flap downward and strike the vertical stabilizer, resulting in the component separating from the horizontal stabilizer and bending the tail boom.
- The crew was properly licensed and medically fit for the operation.