What happened
During an attempt to land from a hover, the helicopter began to oscillate fore and aft, exhibiting signs of apparent ground resonance. At the time of this oscillation, the pilot had applied full power while the collective control remained in the down position. The pilot reportedly did not raise the collective during the event. Following this oscillation, the left skid failed, causing the aircraft to roll onto its left side.
The investigation
The aircraft had previously been involved in an accident involving a tail rotor strike. As part of the repairs for that incident, the four landing gear dampers were serviced. Following those repairs, the helicopter underwent inspection and was signed off for return to service, which included main rotor track and balance tests that showed no discrepancies.
Upon investigation of the recent incident, it was determined that three of the four landing gear dampers had been improperly serviced. Additionally, testing of the main rotor blade dampers confirmed they were free of any malfunction or failure prior to the impact.