Incident Details
On July 24, 2018, about 1800 Pacific daylight time, a Bell UH-1H helicopter, registration N107CH, was substantially damaged during a precautionary landing near Oakdale, California. The pilot was not injured; the passenger sustained minor injuries. The helicopter was registered to Airlift Helicopters Service and operated by the pilot under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed for the cross-country flight, and no flight plan was filed. The flight originated from Madera Municipal Airport (MAE), Madera, California at 1600 and was destined for Lincoln Regional Airport/Karl Harder Field (LHM), Lincoln, California.
Pilot Account
In a post-accident telephone conversation with the National Transportation Safety Board (NTSB) Investigator in Charge, the pilot stated that he was in straight and level flight when he heard a "strange" noise, which he described as sounding like "a tarp in the back of a pickup." He decided to execute a precautionary landing. There were no other indications in the helicopter; all instruments were within normal operating limits, there was no vibration, and the engine was producing power. About 5 feet above the ground, the helicopter entered an uncontrolled climb and yaw. The pilot was unable to recover from the loss of directional control, and the helicopter impacted terrain.
In the NTSB Form 6120.1 "Pilot/Operator Aircraft Accident/Incident Report," the pilot added that, during the descent, the noise "grew louder." The helicopter touched down in the upright position. In the report, the pilot did not mention an uncontrolled climb or yaw.
Passenger Account
In a telephone call to the Federal Aviation Administration (FAA) Inspector, the passenger reported that, while in level cruise flight, he heard a noise. The pilot checked the instrument panel and confirmed that all instruments were within normal operating limits. The passenger noted no vibrations or changes other than the noise. He did not disclose how long the noise was present nor what it sounded like. They made a normal approach with a controlled descent to land, and that was the last thing he remembered surrounding the accident sequence.
Examination
The NTSB Materials Laboratory examined fractured pieces from the main drive shaft and damaged remnants of the swashplate assembly. The main drive shaft and the swashplate support fracture surfaces exhibited features consistent with fracture from overstress. The overstress orientation varied from part to part but was observed in tension, bending, shear, compression, and combinations.
Postaccident examination of the helicopter did not reveal any pre-existing malfunction that would have precluded normal operations.