What happened
On 13 May 2007, a Robinson R22 Beta II helicopter, registration ZS-RTZ, was conducting a local private flight between Wonderboom Aerodrome and Warmbaths. During the return leg of the journey, while flying at a low altitude of approximately 45 knots, the pilot observed the clutch actuator warning light illuminate.
In response to the light, the pilot lowered the collective. Although the warning light subsequently extinguished, it was immediately followed by a low rotor RPM warning. The pilot attempted to recover by performing an aggressive flare using the aft cyclic. This maneuver caused the tail section of the aircraft to strike the ground, followed by the right skid. The aircraft came to rest on a farm approximately 5 nm north of the Carousel Casino. Both the pilot and the passenger escaped the wreckage without injury.
The investigation
SACAA AIID investigators examined the wreckage and the aircraft's maintenance history. The investigation confirmed that the Robinson R22 Beta II was airworthy and had undergone a recent periodic inspection. No mechanical defects were found in the vee-belt drive, the actuator bearings, or the Telatemp indicator.
Technical analysis of the Pilot Operating Handbook (POH) revealed that the clutch light may momentarily illuminate during flight as the belts re-tension. The manual specifies that emergency procedures, such as pulling the clutch circuit breaker and landing immediately, should only be initiated if the light remains on for more than four to six seconds. The investigation determined that in this instance, the light had been active for less than six seconds.
Findings
- The aircraft was properly maintained and possessed a valid certificate of airworthiness.
- The clutch warning light illuminated for a duration of less than six seconds, which is considered normal operation for belt re-tensioning.
- The pilot used incorrect technique by lowering the collective prematurely in response to the brief warning light.
- This action disturbed the pilot's concentration and led to a decay in main rotor RPM, triggering the subsequent impact.