What happened
On 7 April 2008, a flight instructor was conducting a demonstration flight in the Grand Central helicopter general flying area, south of Midrand. The flight, which included a potential student as a passenger, was intended to showcase helicopter capabilities and flight techniques. While climbing to return to Grand Central Aerodrome, the pilot decided to demonstrate an engine failure recovery maneuver.
At an altitude of approximately 350 ft above ground level, the pilot initiated an autorotation. Shortly after the maneuver began, the main rotor RPM dropped to roughly 88%, triggering the low RPM audio and visual warnings. Although the pilot followed the manufacturer's procedures by simultaneously increasing throttle and lowering the collective pitch, the rotor system failed to recover. As the aircraft descended, the pilot attempted to cushion the impact by pulling maximum collective pitch, but the rotor system had already entered a stall state. The Robinson R22 Beta II, registration ZS-RNB, struck the ground with a high rate of descent, causing the left skid to collapse and the aircraft to cartwheel, which ultimately severed the tail boom. Both the pilot and the passenger sustained minor injuries.
The investigation
SACAA AIID investigators examined the flight circumstances, weather conditions, and the aircraft's mechanical state. The investigation established that the aircraft was well-maintained and operating within weight and balance limits. Meteorological data revealed that while the pilot believed the wind was from the north-northeast, the actual prevailing wind was from the west, contributing to a tailwind component during the maneuver. The investigation also noted a high density altitude of 6,500 ft at the time of the accident.
Findings
- The pilot's assessment of the prevailing wind conditions prior to the maneuver was inaccurate.
- The low-altitude nature of the maneuver (350 ft AGL) left the pilot with extremely limited time to react to the decaying rotor RPM.
- The low rotor RPM and subsequent blade stall caused a high rate of descent that could not be arrested.
- There were no mechanical defects or malfunctions found in the aircraft prior to the incident.
Safety action
- It is recommended that aviation training organizations refrain from performing or teaching autorotational maneuvers at altitudes below 800 ft AGL due to the high risk of catastrophic outcomes if the maneuver is not executed perfectly.