What happened
On 17 April 2015, a Robinson R22 Beta helicopter, registration ZS-RBS, was engaged in a game darting operation on a farm south of Somerset East. The pilot was hovering at approximately 130 feet above ground level to monitor a darted springbok and coordinate with a ground recovery team. During this period, the pilot's attention was diverted by a motorcyclist riding toward the herd of animals. While attempting to communicate with the ground crew to intercept the rider, the aircraft began to vibrate significantly.
The pilot noted the activation of the low rotor RPM warning horn and immediately attempted to recover by lowering the collective lever. However, the aircraft failed to regain sufficient RPM and entered a rapid descent. In an effort to avoid a nose-first impact, the pilot pulled the nose up, but the helicopter struck the ground tail-first. The impact was severe enough to break the skid and cause the main rotor to sever the tail boom, resulting in the total destruction of the aircraft. Both occupants sustained minor injuries and were treated at a local hospital.
The investigation
SACAA AIID examined the flight history, maintenance records, and the physical wreckage. The investigation confirmed that the aircraft had been maintained according to approved procedures and was in good working condition. The investigation also noted that the operator's Air Operator Certificate (AOC) had expired a few days prior to the accident.
Investigators analyzed the flight dynamics, focusing on the aircraft's sensitivity to control inputs. The study established that the pilot's focus on the external disturbance—the motorcyclist—led to a lack of monitoring regarding engine power and pitch coordination. This lack of oversight allowed the aircraft to enter a critical aerodynamic state while hovering out of ground effect.
Findings
- The primary cause of the accident was the helicopter entering a vortex ring state at a low altitude, which left the pilot with insufficient height to execute a recovery.
- The pilot's operational focus was interrupted by the presence of a motorcyclist, leading to improper power and pitch coordination.
- The Robinson R22 Beta is highly responsive to control inputs, making precise coordination essential during low-altitude maneuvers.
- There was insufficient power available to maintain the hover during the onset of the aerodynamic instability.