Enstrom F-28C-2 N5694A accident near Blair, Nebraska

Probable cause

The failure of a tail rotor pitch change link due to the retaining bolt becoming separated in flight. Contributing to the accident was the pilot’s inadequate preflight inspection.

NTSB analysis

The pilot was conducting an aerial observation flight in a helicopter when he felt a high vibration in the tail rotor system in conjunction with a sharp jerk in the anti-torque pedals. The pilot autorotated to a wet field and the helicopter subsequently rolled over. A postaccident examination of the helicopter revealed that a pitch link retaining bolt had come loose from the pitch link attachment horn. The bolt and its associated hardware separated in flight and the bolt hole where the pitch link attached was elongated. According to the helicopter’s preflight inspection checklist, the pitch link should have been checked before flight for binding or looseness; however, the pilot could not recall if he actually checked it. The helicopter underwent a 100-hour maintenance inspection two weeks before the accident. At that time, the maintenance manual required an inspection in which the pitch links would have to be disconnected then reassembled. Since the pitch link retaining bolt and its associated hardware were never recovered, it could not be determined if the pitch link assembly had been properly installed or torqued at the last inspection. The pitch link failure occurred about 14 hours after this inspection. The Federal Aviation Administration reported that they were not aware of any instances prior to this accident where the tail rotor pitch link assemblies became loose and failed prematurely after proper installation.

Text from the NTSB. Open the NTSB docket for CEN11LA414 for the full record.