What happened
On 29 October 2013, a Robinson R22 Beta helicopter, registration ZS-RTV, was conducting a private flight from Mossel Bay Aerodrome toward Knysna. While cruising at approximately 1100 feet AMSL along the coast near Herolds Bay, the engine began backfiring, accompanied by significant vibration and yawing. The pilot observed manifold pressure increasing sharply from 20 to 28 inches mercury, followed by a rapid drop in both engine and rotor RPM.
Recognizing the imminent engine failure, the pilot declared an emergency with George Air Traffic Control and maneuvered toward an open field on a farm near George Aerodrome to perform an autorotative landing. During the touchdown on the uneven terrain, the aircraft bounced and rolled onto its left side. The pilot sustained a minor head injury from contact with the cyclic, but no other injuries were reported. The helicopter sustained substantial damage to its fuselage, rotor systems, and tail boom.
The investigation
SACAA AIID investigators examined the wreckage of the ZS-RTV and the engine components. The inspection of the Lycoming engine revealed that the exhaust pushrod on the number one cylinder was both bent and fractured. Further examination of the cylinder rocker box showed that the exhaust valve had fractured, leaving the stem lodged within the cylinder head.
Additionally, the investigation looked into the operator's recent maintenance changes. It was noted that the operator had transitioned from using Aeroshell Aviation W100 Plus oil to Exxon Elite 20W-50 oil across their fleet approximately three weeks prior to the accident. A similar incident involving a bent pushrod had occurred on another of the operator's helicopters during a hover just weeks earlier.