CEN13FA025 · Agusta SPA AW139

The flight crew was repositioning the helicopter to another landing pad when the accident occurred. According to the flight crew and flight data recorder (FDR) data, as the helicopter was touching down, it began to experience severe vertical vibrations and to oscillate violently. The pilot reported that he lowered the collective but that the vibrations and oscillations intensified. The pilot then increased the collective to lift the helicopter off the ground. The helicopter became airborne, but the violent oscillations and vibrations continued. The pilot initiated a left pedal turn to avoid another helicopter, at which time, the oscillations and vibrations were so severe that the pilots' headsets came off of their heads. The helicopter entered a spin and impacted the grass hard while moving laterally to the left. The pilots shut down and then exited the helicopter.

The blue main rotor blade damper was replaced the night before the accident. A maintenance test flight was performed following the replacement. The flight crewmembers who flew the test flight reported that there was a slight vibration from the main rotor system and that one of the five main rotor blades had a "slight dip" in its track. There was no record of the main rotor blade out-of-track discrepancy nor of a main rotor track and balance inspection being performed subsequent to this flight. Although an out-of-track blade could cause a persistent vertical vibration, an examination of the main rotor blades, elastomeric bearings, main rotor dampers, main rotor rod ends, main gearbox attachment points and antitorque beam, and automatic flight control system did not reveal any anomalies that could account for the vertical vibrations reported by the flight crew and recorded on the FDR.

Verbatim NTSB analysis and probable cause from the NTSB dataset