CHI06LA027 · Agusta A109-E

The helicopter sustained substantial damage during an aborted takeoff from a helicopter-landing pad. The pilot stated that he started the helicopter and "performed a full run-up of both engines and all systems." He reported, "Both engine FADEC [Full-Authority Digital Engine Control] Power Management Switches (PMS) were verified as being in the 'Flight' position, the collective-mounted 100 percent/102 percent switch was in the '102' position, and the number 1 Electronic Display Unit (EDU) showed three vertical yellow lines representing the rpm of both engines as being at 102 percent and that the rotor rpm (Nr) was co-joined with them." He reported that he pulled the helicopter into a five-foot hover. After about 30 seconds of normal hovering flight, the pilot heard a "bang." The pilot reported that the helicopter started to settle vertically downwards, and that he glanced at the number 1 Electronic Display Unit and saw "multiple caution and warning lights." He reported that the aircraft was oscillating laterally as it settled, and that there was a rapid loss of rotor rpm. He used the collective pitch lever to cushion the landing with the remaining rotor rpm. He reported, "As soon as the left main wheel gently touched down the aircraft went into a violent lateral oscillation which was clearly ground resonance. This resonant oscillation increased in severity even though I had the collective pitch lever in the full down position." The left main landing gear collapsed and the helicopter settled onto its left sponson. The tail rotor blades contacted the ground. The helicopter continued to oscillate laterally and the nose of the helicopter swung to the left following main rotor rotation. The pilot shut down both engines and the main rotor blades coasted to a stop. The on-site examination revealed that the damage to the helicopter was consistent with ground resonance. Both engines were run on an engine test stand and no anomalies were evident that would preclude normal engine operation. The examination of the non-volatile memory of the engine electronic controls (EEC's) for both engines did not reveal any preexistent anomaly or fault codes associated with the accident flight. The inspection of the flight controls and aircraft systems did not reveal any anomalies associated with a preexisting condition.

Verbatim NTSB analysis and probable cause from the NTSB dataset