Bell 206B N3181J accident near Spicewood, Texas

Probable cause

The pilot did not maintain adequate rotor rpm during a low-altitude maneuvering flight.

NTSB analysis

While maneuvering the helicopter at an altitude of about 400 feet above ground level, the pilot heard the low rotor aural warning in his headset and observed that the rotor speed gauge was reading about 80 percent and decreasing. He lowered the collective, initiated a left turn, and began an autorotative descent to hilly terrain that contained trees and power lines. During the autorotation, the pilot attempted to avoid the power lines, and the helicopter impacted terrain. Although the pilot reported that he believed the engine lost power, a postaccident examination of the helicopter revealed no evidence of any preimpact mechanical failures or malfunctions. Additionally, the helicopter’s engine was run in a test cell for 1 hour 50 minutes with no anomalies detected.

Text from the NTSB. Open the NTSB docket for CEN11LA646 for the full record.