History of Flight
On 29 October 2013 at 0630Z, the pilot departed Mossel Bay Aerodrome in a Robinson R22 Beta helicopter (registration ZS-RTV) on a private flight to Knysna, with the intention of returning to Mossel Bay. After takeoff, the pilot contacted George Air Traffic Control for routing and was instructed to orbit before being cleared inbound. While cruising at approximately 1100 feet AMSL and 75 knots near Herolds Bay, the engine began backfiring. The helicopter yawed and vibrated, and the manifold pressure increased from 20 to 28 inches of mercury before rotor and engine RPM dropped sharply. The pilot declared an emergency and initiated an autorotative landing after the engine failed, maneuvering toward an open field. During touchdown, the helicopter bounced and rolled onto its left side due to uneven ground.
Injuries and Damage
The pilot sustained a laceration to the head from impact with the cyclic and was transported to hospital with minor injuries. The helicopter sustained substantial damage, including to the main rotor, tail rotor, tail boom, skids, fuselage, and windscreens.
Investigation Findings
Examination of the engine revealed that the exhaust pushrod on cylinder No. 1 was bent and fractured. This was caused by a sticky exhaust valve, which led to the engine failure. The helicopter's weight and balance were within limits, and no pre-existing defects were recorded in the maintenance logs. Weather at the time was clear with light winds.
Probable Cause
The probable cause of the accident was an unsuccessful autorotation following an engine failure, which resulted from a sticky exhaust valve that caused a bent pushrod and subsequent engine failure.