What happened
On the afternoon of 3 October 2024, a private flight departing from Dibeng Airfield in the Northern Cape Province resulted in the destruction of a Calidus gyrocopter, registration ZU-RHN. The flight was being conducted under Part 91 regulations in clear visual meteorological conditions.
During the take-off sequence, the pilot engaged the pre-rotator system but disengaged the shaft before the rotor blades reached the minimum required speed of 2-20 RPM. Despite the insufficient rotational speed, the pilot proceeded with the take-off roll, intending for the rotor to accelerate via airflow. Additionally, the pilot did not apply enough aft control to achieve the necessary angle of attack. As the aircraft moved forward, the low rotor RPM caused the blades to flap excessively. This instability created significant turbulence, causing the pilot to lose grip of the control stick and resulting in the aircraft rolling to the right. The impact left the aircraft destroyed, with the tail section separating from the fuselage and the cockpit glass shattering, though the pilot escaped without injury.
The investigation
SACAA AIID examined the aircraft's maintenance and operational history. The ZU-RHN had undergone its last annual inspection approximately one month prior to the accident. The investigation also reviewed the pilot's credentials, confirming the pilot was suitably qualified, licensed, and medically fit for the operation. Meteorological data indicated a light 4-knot crosswind, which was well within the aircraft's operational limits and was not a contributing factor to the event.
Findings
- The primary cause of the accident was rotor blade flapping triggered by the premature disengagement of the pre-rotator before reaching the manufacturer-specified 220 RPM.
- The pilot's decision to continue the take-off roll despite insufficient rotor speed was a critical error that bypassed safe operating procedures.
- The combination of low rotor RPM and the aircraft's forward taxi speed created unequal lift across the rotor disk, leading to the unstable flapping motion.
- The pilot failed to maintain the necessary control stick position to achieve the required angle of attack for a safe lift-off.