NTSB Identification: WPR10LA336
14 CFR Part 91: General Aviation
Accident occurred Thursday, July 08, 2010 in Arlington, WA
Probable Cause Approval Date: 05/11/2011
Aircraft: JOHNSON HELICYCLE, registration: N62AJ
Injuries: 1 Minor.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot reported that after an uneventful flight, he entered a left downwind traffic pattern for his intended landing area. As he lowered the collective to initiate a descent, he immediately experienced a severe vibration. The pilot stated that the vibration was so violent that it was impossible to read the cockpit instruments. He raised and lowered the collective and noted no change in the vibration. The pilot then initiated an autorotation to an open field adjacent to his intended landing area. The helicopter landed hard and came to rest upright. A postaccident examination of the helicopter revealed that the tail rotor was separated from the tail boom with additional damage observed to the fuselage and main rotor blades. Flight control continuity was established throughout the helicopter's flight control system. The source of the vibration could not be determined.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

An undetermined airframe vibration which led to precautionary autorotation and hard landing.

Full narrative available

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