Enstrom F28 N63VP accident near Twin Falls, Idaho

Probable cause

The pilot's inability to maintain helicopter control during cruise flight due to the failure of the No. 2 main rotor Lamiflex bearing. Contributing to the accident was the pilot's decision to operate the helicopter with a known deficiency and the helicopter’s noncompliance with the mandatory scheduled inspection of the main rotor bearings.

NTSB analysis

The pilot reported that on a previous flight, he encountered an uncommanded roll, so he checked the three main rotor Lamiflex bearings prior to departure. He said one bearing showed no indication of a pending failure, the second showed some indication of approaching failure, and the third showed a minor indication that it was beginning to fail. From past experience, the pilot said that he believed that he still had several hours before the bearings would fail and that he could safely proceed with the flight. A few miles from the intended destination, a vibration started and became progressively worse to the point where the pilot was losing control of the helicopter. The pilot subsequently made what he described as a “controlled crash landing,” which resulted in substantial damage to the helicopter. A postaccident examination revealed that the No. 2 main rotor Lamiflex bearing failed, which resulted in the loss of control. A review of maintenance logbooks found that the helicopter was not in compliance with either its annual inspection requirement or with FAA Airworthiness Directive 94-17-15, which required repetitive inspections of the helicopter’s main rotor Lamiflex bearings.

Text from the NTSB. Open the NTSB docket for WPR12LA219 for the full record.