What happened
On the morning of 13 June 2023, a training flight involving an instructor and a student pilot ended in a crash on a taxiway at Grand Central Airport, Gauteng. The flight, operated by Ultimate Heli, began in Midrand with the intention of performing circuits and emergency procedures. The crew was operating the Robinson R22 Beta, registration ZS-HXU, under visual meteorological conditions.
During the fifth circuit of the session, the crew initiated an autorotation maneuver at approximately 70 and 150 feet above ground level. As the student pilot attempted to apply power to recover from the maneuver, the engine failed to respond. The instructor realized the engine had stopped and attempted to take control and restart the engine, but there was insufficient time to prevent the descent. Air traffic controllers at Grand Central Airport observed the Robinson R22 Beta losing altitude rapidly and yawing to the left before impacting the taxiway near Runway 17. Both occupants evacuated the aircraft unassisted and were not injured, though the helicopter suffered substantial damage.
The investigation
SACAA AIID investigators examined the aircraft and the environmental conditions at the time of the accident. Post-accident testing of the engine, conducted with the rotor blades removed and the clutch disengaged, showed that the engine operated satisfactorily, suggesting no mechanical failure was present.
Weather data from the South African Weather Service indicated a temperature of 6.8°C and a dew point of 1.5°C. This resulted in a dew point depression of 5.3°C and a relative humidity of approximately 70%, conditions that present a high probability for icing. The investigation also reviewed the crew's actions regarding the aircraft's carburettor heat system during the maneuver.
Findings
- The engine lost power during the autorotation practice due to carburettor icing.
- The crew failed to switch the carburettor heat knob to the "ON" position during the exercise, which is a requirement of the Pilot's Operating Handbook when power settings are low (between 14-15 inches of mercury) or during autorotations.
- The aircraft was properly maintained, with a valid Certificate of Airworthiness and a recent periodic inspection completed only days prior to the event.