Incident Overview
A helicopter pilot reported that while cruising at 300 feet above ground level (AGL), a sudden violent shudder coursed through the entire helicopter. The shudder then ceased. The pilot noted no subsequent change in flight characteristics or engine power.
Pilot Actions
In response to the event, the pilot elected to make a precautionary landing. He chose to fly directly to the ground without performing a hover. During this landing, the tail boom contacted the ground. Subsequently, the main rotor blades struck the tail boom.
Investigation Findings
An investigation into the incident did not identify a cause for the initial shudder. No mechanical or other explanation was found for the vibration that prompted the precautionary landing.