What happened
On 19 April 2023, a flight instructor and a student pilot were conducting an authorized training flight near Mossel Bay Aerodrome (FAMO) in the Western Cape. The crew was performing routine autorotation exercises in a Guimbal Cabri G2, registration ZS-HKCT, under visual meteorological conditions.
During the third exercise, while climbing to 800 feet, the engine failed to respond to throttle inputs at approximately 300 feet. The instructor observed a low oil pressure warning and noted a decay in the main rotor RPM. Taking control of the aircraft, the instructor initiated a flare at roughly 40 feet. The helicopter struck the ground in an open field approximately 1.6 nautical miles west of FAMO with a touchdown speed of about 15 knots. The impact caused the aircraft to bounce and rotate 90 degrees, during which the main rotor blades severed the tail boom. The instructor sustained a minor head injury, while the student pilot remained uninjured.
The investigation
SACAA AIID investigators examined the aircraft, the maintenance history, and the environmental conditions. The investigation confirmed that the helicopter was airworthy, with a valid Certificate of Airworthiness and recent maintenance completed. Fuel and oil levels were sufficient, and no fuel contamination was detected. The weather was clear, though investigators noted that conditions were favorable for potential carburetor icing, which could not be ruled out as a cause for the engine stoppage.
Findings
- The engine failure occurred during a power-off descent phase of an autorotation exercise.
- Insufficient rotor inertia prevented the blades from cushioning the landing during the flare.
- The instructor had not been specifically trained by the training academy to perform autorotations to a full ground touchdown.
- The sudden impact and subsequent bounce caused the tail boom to be struck by the main rotor blades.