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Conclusions

Summary

3 Conclusions

3.1 Findings
  • There was no witness or mechanical evidence to indicate any problems with the flight controls, fuel system or engine prior to the event.
  • Failure of the forward flex plate resulted in drive to the main rotor gearbox being partially disconnected.
  • The failed forward flex plate coupling punctured one or both the helicopter fuel tanks and the stainless steal engine compartment firewall.
  • The helicopter settled heavily and impacted with terrain.
  • The helicopter was destroyed by impact forces and a post-impact fire.
  • Egress from the helicopter was hampered by the unusual attitude of the cabin which caused extended exposure of the survivor to the post-impact fire.
3.2 Significant factors

One of the two bolted joints linking the flex plate to the  main rotor gearbox yoke in the forward flexible coupling was previously assembled incorrectly, resulting in a lack of clamping force and subsequent fatigue failure of the flex plate and loss of drive to the main rotor gearbox.

 
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