What happened
On 01 August 2015, a Robinson R44 II helicopter, registration ZS-SBM, was conducting a training flight from Wonderboom Aerodrome to Aeropark Zynkraal. The flight, involving a flight instructor and a student pilot, was intended for practicing circuits and autorotation maneuvers.
During the approach to runway 27 at Aeropark Zynkraal, the student pilot initiated an autorotation. As the aircraft descended, the rotor RPM began to decay. The instructor took control of the aircraft at approximately 200 feet AGL, attempting to recover the rotor RPM by lowering the collective and increasing the throttle. Despite these efforts, the RPM continued to drop. At roughly 100 feet AFL, the instructor performed a flare to level the aircraft, but the low rotor RPM persisted. As the instructor attempted a run-on landing, the helicopter began to vibrate violently. The left skid struck the runway and broke off, and the main rotor blades struck the ground three times, severing the tail boom into multiple pieces. The aircraft rolled onto its left side and came to a stop in the center of the runway. Both occupants escaped the accident without injuries.
The investigation
The SACAA AIID investigation focused on the sequence of the maneuver and the mechanical state of the aircraft. Investigators confirmed that the Robinson R44 II was properly maintained, with a valid Certificate of Airworthiness and Certificate of Release to Service. The instructor and student pilot both held valid licenses and medical certificates. The investigation also reviewed the meteorological conditions, which were clear with no cloud cover and light winds, ruling out weather as a contributing factor.
Findings
- The primary cause of the accident was a hard landing resulting from an unsuccessful autorotation attempt.
- A significant contributing factor was the incorrect autorotation technique employed by the student pilot, specifically the failure to lower the collective when entering the autorotation.
- The aircraft sustained substantial damage to the fuselage, windshield, tail boom, and main rotor blades.