Accident Overview
At approximately 10:00 UTC on 1 February 2010, a Hughes 269C helicopter (registration ZS-HWH) was at Wonderboom Aerodrome (FAWB) in Gauteng, South Africa, preparing for a training flight. The pilot, accompanied by a flight instructor, was conducting a before-take-off checklist. During a magneto check at approximately 3200 engine RPM while still on the ground, the helicopter experienced excessive resonance.
The pilot immediately closed the throttle, but the helicopter became uncontrollable. The tail rotor blades made contact with the ground, and the helicopter spun in a clockwise direction. The main rotor blades severed the tail boom, and the helicopter was destroyed. No damage was caused to the helicopter landing pad.
Injuries and Damage
The flight instructor sustained minor injuries (a laceration to the head) and was discharged from hospital the same day. Neither occupant was killed. The helicopter was destroyed; the engine and cockpit seats were undamaged.
Probable Cause and Contributing Factor
The probable cause was severe ground resonance as a result of incorrect landing gear damper pressures, rendering the helicopter uncontrollable and leading to rotor contact. A contributing factor was the failure of the landing gear damper attachment points due to the severe ground resonance.
Landing Gear Damper Findings
All four landing gear dampers were removed and tested. The tests revealed that all four were improperly charged: three were in excess of full stroke limits, and the fourth was out of limits for the intermediate range. The effect of excessive pressure in the dampers is a loss of damping and lack of attenuation of main rotor oscillations.
Personnel and Aircraft Information
The pilot held a Commercial (H) licence with 202.9 total flying hours (176.3 on type). The instructor held a Commercial (H) licence with 3,900 total hours. The helicopter, a Hughes 269C manufactured in 1987, had 10,901.4 total airframe hours. The last mandatory inspection was certified on 9 September 2009.
Meteorological Conditions
Wind was southerly at 5 knots, visibility greater than 10 km, temperature 28°C, and cloud cover nil.
Additional Details
The accident was regarded as survivable due to low impact forces and the occupants wearing safety harnesses. There was no pre- or post-impact fire. The helicopter was not fitted with cockpit voice or flight data recorders, which were not required.