History of Flight
On 20 March 2008 at 1120Z, the pilot of a Robinson R22 Beta II helicopter, registration ZS-RTV, departed from Brits aerodrome on a private flight to Rustenburg aerodrome. While flying over a residential area in Rustenburg at approximately 1 500 feet above ground level, the pilot lowered the collective pitch lever. The engine RPM immediately decreased to idle and remained there despite any throttle input. The pilot then lowered the collective and initiated an autorotation. The helicopter landed hard in open veld about 1 km from the point where the autorotation began. The accident occurred during daylight at coordinates S25° 38.776′ E027° 15.054′, elevation 3 588 feet above mean sea level.
Injuries and Damage
The pilot sustained no injuries. The helicopter suffered extensive damage to the main rotor, tail rotor, tail boom, and skid gear.
Investigation Findings
Examination of the wreckage revealed a broken throttle linkage (part no. A759‑1) at the overtravel spring assembly. The throttle linkage was sent to a metallurgical laboratory, which concluded that the component had been subjected to tensile overload during operation or fitment, leading to crack initiation in the thread root areas. These cracks then propagated as fatigue fractures under vibration and operating conditions. No other engine controls were damaged. The helicopter had approximately 10 US gallons of Avgas 100LL fuel remaining. No evidence indicated that the throttle linkage had been damaged or replaced prior to this flight.
Probable Cause
The probable cause of the accident was an unsuccessful autorotation landing following the inflight failure of the throttle linkage due to fatigue, resulting in the engine spooling down to idle and a hard landing.