CEN20LA187

While cruising about 500 feet above ground level, the pilot of the helicopter felt a vibration and entered a precautionary autorotation, though he did not observe any caution or warning lights or horns associated with the vibration. The pilot turned toward an open field for landing and, after clearing some trees, the low rotor rpm horn activated. He reduced collective and made a hard run-on landing, during which the helicopter slid about 20 to 30 ft on its skids before coming to rest upright. The main rotor drooped and one blade struck the tail boom, severing the tail rotor drive shaft and resulting in substantial damage. There was also crush damage to the underside of the tail boom caused by impact forces. The pilot could not describe the location or frequency of the vibration, and the passenger reported that he felt no vibration. Postaccident and follow-up inspections of the helicopter by revealed no anomalies that would have resulted in the vibration. Although the source of the vibration could not be determined, it is likely that the hard landing was the result of the pilot's failure to maintain rotor rpm during the precautionary autorotation.

On May 20, 2020, about 0933 eastern daylight time, an experimental exhibition category Bell OH-58A helicopter, N153SA, was substantially damaged when it was involved in an accident near West Bank, Michigan. The commercial pilot and passenger were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 personal flight. The pilot told Federal Aviation Administration (FAA) inspectors that he and his passenger departed Peach Lake Heliport (89MI), his private heliport for a local flight to Midland, Michigan, to observe recent flood damage. During the return flight, at an altitude of about 500 ft above ground level, the pilot felt an airframe vibration, and he immediately entered a precautionary autorotation. He did not observe any caution or warning lights or horns associated with the vibration. The pilot made a 200° left turn to an open field, and after the helicopter cleared some trees during the approach, the low rotor rpm horn activated. The pilot reduced collective and made a hard run-on landing. The helicopter slid about 20 to 30 ft on its skids before it came to rest upright. The main rotor drooped, and one blade struck the tail boom, severing the tail rotor drive shaft; the underside of the tail boom also sustained impact damage. The pilot could not describe to Federal Aviation Administration inspectors the location or frequency of the vibration, and the passenger reported that he felt no vibration. Postaccident and follow-up inspections by the pilot's mechanic found no evidence of the source of the vibration.