History of Flight
On 10 April 2010, a certified flight instructor and a student pilot conducted a training flight under Visual Flight Rules (VFR) from Cape Town International Aerodrome (FACT) with the intention to return. The helicopter was refueled before departure. After clearance from FACT tower, the student pilot lifted off. When the helicopter was stable and hovering at about two feet above the helipad, the instructor took control and positioned it for transition. While hover taxiing, the instructor heard a loud bang from the engine, which immediately stopped. The helicopter spun approximately 90 degrees before coming to rest on its skids. Fuel (Avgas LL100) was observed leaking; the instructor shut off the fuel valve, pulled the mixture, and turned off all switches. Both occupants vacated the helicopter unharmed.
Damage
The helicopter sustained substantial damage. Examination revealed that the forward flex plate on the gearbox sheared off. The drive shaft ripped open both main and auxiliary fuel tanks, pulled wiring out of the loom and off the frame. The aft flex plate on the free wheel bent but did not break. The clutch was fully engaged and bent to one side. Both V-belts climbed off the pulleys and sheared. The sheave alignment rod was bent and the rod end pulled off the bearing. The aft cross tube was bent from hard landing.
Metallurgical Examination
Expert metallurgical examination determined that the forward flex plate failed in fatigue on takeoff, resulting in extensive damage.
Probable Cause
The forward flex plate fractured after lift-off, resulting in a tail rotor drive shaft failure.
Personnel and Meteorological Information
The instructor held a Commercial pilot licence with 2015.6 total hours and 870 hours on type. The student pilot was not identified. Weather at the time was clear with visibility 10 km, wind from 150° at 15 knots, temperature 17°C, and few clouds.