20260717012439I

The weather conditions at the time included good visibility and winds from the south at 7 TO10 mph. The aircraft was located between hangars on the southwest side of the Arlington Municipal Airport (kawo) while conducting a maintenance ground run-up and leak check; there was no intent to fly the aircraft during this operation, it was for maintenance purposes only.

During the operation, contributing factors included a noticeable out-of-balance condition and an extremely large split in the main rotor blade track that caused the aircraft to go into ground resonance. The mechanic/pilot picked the helicopter into a hover to mitigate the amount of frequency running through the aircraft. On the first attempt to set the aircraft back down, it went into ground resonance immediately. The mechanic/pilot then decided to hover taxi the aircraft to get the rotor system to reset itself and then attempted to set the helicopter down at the end of the taxi-way with success. This led the mechanic/pilot to believe that the rotary friction dampers needed to be exercised and that, along with the track and balance. The mechanic/pilot then picked the helicopter into a hover and taxied back to the hangars. The mechanic/pilot set the aircraft completely on the ground with no ground resonance, but as mechanic/pilot decreased throttle, the aircraft started to go into ground resonance and destroy itself. The main rotor mast detached, and there is substantial damage to the airframe, rotor blades, and landing gear.