History of Flight
On September 11, 2019, at about 1300 Pacific daylight time, a Sikorsky S-58ET helicopter, registration N1168U, was substantially damaged during an accident near Azusa, California. The pilot, who was the sole occupant, was not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a ferry flight.
The pilot reported ferrying the helicopter from Shafter Airport-Minter Field (MIT), Shafter, California, to Corona Municipal Airport (AJO), Corona, California. While cruising at approximately 1,000 ft above ground level and an airspeed of 110 knots, the pilot heard and felt a loud bang without the onset of noise or vibration. The helicopter then began to yaw to the right. The pilot initiated an immediate autorotation and landed in a baseball field.
A postflight inspection revealed that one tail rotor blade had separated from the tail rotor assembly. The three remaining tail rotor blades, still attached, exhibited dents and chordwise bends. The 90° gearbox had fractured, exposing internal gears, and the vertical stabilizer was impact damaged.
Aircraft Information
Maintenance records indicated that the separated tail rotor blade had been repaired on April 20, 2007. Documents noted that the repair details were on file at the performing repair station; however, the company stated it retained no documents related to the work and could provide no additional information. The paint had been removed, and the blade was refinished and static balanced, after which it was deemed airworthy.
The blade was installed on the accident helicopter on May 13, 2013, when the airframe had accumulated 18,897 total hours. At that time, the blade had 885 total hours and an “on condition” retirement life, and it was in compliance with all applicable airworthiness directives and service bulletins.
The mechanic who performed the daily inspection on the morning of the accident reported wiping down the tail rotor blades and observing no working metal, cracks in the paint, or evidence of a crack.
Wreckage and Impact Information
The separated section of the tail rotor blade was not recovered. The shank and the other three blades were sent to the National Transportation Safety Board’s Materials Laboratory for examination. Fractographic examination of the shank revealed that the blade had separated perpendicularly to its length along a chord plane about 3 inches from the bottom of the blade.
A thumbnail-shaped pattern consistent with fatigue was observed emanating from one side of the blade, propagating through approximately three-quarters of the blade. No nicks, gouges, damage, or contamination were found at the fatigue origin. Further examination showed that the tail rotor blade shank and the remaining three blades met the design specifications in the engineering drawings.