Accident Summary
On September 15, 2011, at 0915 central daylight time, a Bell 206B single-engine helicopter, registration N3181J, sustained substantial damage when it impacted terrain while maneuvering near Spicewood, Texas. The private pilot and a passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under 14 Code of Federal Regulations Part 91. The local flight had departed from Spicewood Airport (88R) at approximately 0815.
Pilot Report
According to the pilot, the flight departed with approximately 70 gallons of fuel. About one hour into the flight and four miles southwest of the airport, he heard the low rotor aural warning in his headset and observed the rotor speed gauge indicating approximately 80 percent and decreasing. At an altitude of roughly 400 feet above ground level, the pilot lowered the collective, initiated a left turn, and began an autorotative descent toward hilly terrain containing trees and power lines. During the autorotation, he attempted to avoid power lines, but the helicopter impacted the terrain. Subsequently, the helicopter rolled over and came to rest on its right side. After the impact, the engine was still operating at an unknown power level, and the pilot used the fuel cutoff to stop the engine. The pilot stated that he believed the helicopter experienced an uncommanded reduction in engine power. He reported that the wind was calm and the temperature was 86 degrees Fahrenheit.
Postaccident Examination
Examination of the helicopter showed that the tail boom had separated and the main rotor blades were bent and twisted. No external damage was noted on the Allison 250-C20B engine. The engine was covered in fire suppressant material, applied by fire rescue as a precaution due to dry vegetation. The engine fuel, oil, and pneumatic lines exhibited no visual damage, and all connections were secure. The engine was removed and sent to Rolls-Royce Corporation for further examination. A review of maintenance records revealed that the helicopter underwent its most recent annual inspection on February 22, 2011. At the time of the accident, the engine had accumulated 14,459 total hours and 107 hours since compressor and turbine section overhaul.
Engine Examination
On November 8, 2011, the engine was examined by the NTSB and Rolls-Royce Corporation. The N1 drive train remained rotationally free, while N2 remained locked. The turbine area was flushed with water and an approved alcohol solution, at which time the fire suppressant material was cleared, and N2 became rotationally free. The engine was then placed into a test cell and run for approximately 1 hour and 50 minutes according to Rolls-Royce production test specifications, with no anomalies noted. A Pc system check performed after the engine run detected no leaks.