What happened
On 10 April 2010, a Robinson R22 Beta helicopter, registration ZS-SCS, was conducting a training flight at Cape Town International Aerodrome. The flight, involving a certified flight instructor and a student pilot, began with a standard takeoff under Visual Flight Rules. After the student pilot initially took control for liftoff, the instructor took over to transition the aircraft into a hover.
While the aircraft was hover taxiing just above the helipad, a loud bang originated from the engine area. The engine immediately ceased operation, causing the helicopter to spin approximately 9 and 90 degrees before settling on its skids. Following the impact, the instructor identified a fuel leak from the aircraft's tanks. The instructor acted quickly to shut off the fuel valve and cut the mixture and switches. Both occupants exited the aircraft without injury, though the helicopter sustained substantial damage.
The investigation
SACAA AIID investigators examined the wreckage and the aircraft's maintenance history. The investigation confirmed that the aircraft had been properly maintained, with the last mandatory periodic inspection completed only 24.9 hours prior to the accident. Meteorological conditions were clear with good visibility.
Technical analysis of the wreckage revealed extensive damage caused by the failure of the tail rotor drive shaft. The shaft's movement had torn through both the main and auxiliary fuel tanks, severed electrical wiring, and damaged the clutch and V-belts. A metallurgical examination of the components was central to the investigation.
Findings
Detailed metallurgical testing determined that the forward flex plate failed due to fatigue. The crack had originated under the bolted washers and spread outward. Evidence suggested that this fatigue cracking had been progressing over several previous flights. Because the crack was located beneath the bonded reinforcement and washers, it was not detectable through standard general visual inspections.
Safety action
Following the findings, it was recommended that the SACAA Airworthiness Department, in coordination with the FAA, review the necessity of establishing specific service life limits and defined inspection intervals for forward flex plates installed on Robinson R22 series helicopters.