Incident Overview
On May 20, 2012, at approximately 0900 mountain daylight time, an Enstrom F-28F helicopter, registration N63VP, experienced a control malfunction and made a precautionary landing near the Twin Falls Airport (TWF) in Twin Falls, Idaho. The helicopter sustained substantial damage. The private pilot, who was the sole occupant and registered owner, was not injured. Visual meteorological conditions prevailed for the cross-country flight, which was conducted under 14 Code of Federal Regulations Part 91. No flight plan was filed. The flight had departed Elko, Nevada, about 0615 Pacific daylight time, with TWF as its intended destination.
Pilot Report
According to a report submitted to the National Transportation Safety Board (NTSB) investigator-in-charge, the pilot noted that on a flight a few days prior, the helicopter exhibited a tendency to roll left without sufficient trim to neutralize the roll. The pilot's prior experience indicated that this condition could signal a possible failure of the main rotor Lamiflex bearing, typically occurring within about 15 hours of such indications. During the preflight inspection before the accident flight, the pilot examined the main rotor bearings by pulling back the plastic covers. He observed that bearing 1 showed no signs of impending failure, bearing 2 showed some indications that it was approaching failure, and bearing 3 showed minor indications of initial degradation. Based on his previous experience, the pilot judged the trip could be safely flown.
As the flight neared its destination, about 10 to 15 miles south of TWF and immediately after contacting the TWF air traffic control tower, a slight vibration began. The vibration rapidly intensified. The pilot notified the tower controller that he was experiencing a rotor bearing failure and believed he could still reach the airport. However, the situation worsened to the point where the pilot lost full control of the helicopter. With only partial control and unsure of a safe landing, the pilot experienced low rotor rpm. He lowered the collective to recover rotor speed and executed what he described as a "controlled crash landing." The helicopter impacted the ground hard in a nose-low attitude, coming to an abrupt stop upright but tilted slightly to the left. The tail boom and tail rotor assembly separated and were found about 30 to 40 feet to the right of the helicopter.
Examination Findings
A Federal Aviation Administration (FAA) aviation safety inspector examined the helicopter at the site and determined that the #2 main rotor Lamiflex bearing had failed. This failure resulted in the uncontrollable condition of the helicopter and led to the forced landing. The inspector also noted that the helicopter was not in compliance with its annual inspection requirement and was not in compliance with FAA Airworthiness Directive (AD) 94-17-15. This AD required initial and repetitive inspections for delamination of the main rotor feathering elastomeric Lamiflex bearing to prevent bearing failure, abnormal vibrations, and subsequent loss of control.