Accident Details
On January 23, 2022, about 1030 Pacific standard time, a Bell UH-1E helicopter, registration N333XL, was substantially damaged when it struck terrain near Gustine, California. The pilot, the sole occupant, was not injured. The helicopter was being operated under 14 CFR Part 137 for aerial application.
The pilot reported that he was applying herbicide to a wheat field on the third load of the day after about 45 minutes of flight. While at the apex of a turn, he lost control of the helicopter, which then descended and impacted the ground. The impact substantially damaged the main rotor system, tailboom, and fuselage. The pilot shut off the fuel boost and master electrical switch and exited through the roof window.
Post-Accident Examination
Photographs provided by the pilot showed the helicopter resting on its left side in an open, level field. All major components were within the debris area. The tailboom had partially separated from the fuselage. One main rotor blade had separated about 24 inches outboard of the blade grip; the other remained attached with upward bending near the grip. The tail rotor assembly and 90° gearbox remained attached to the vertical stabilizer.
The 90° gearbox exhibited a breach in the housing where an internal gear had protruded. Green paint around the breach was thermally damaged, and no oil was observed near the exposed area. The gearbox was examined at the NTSB Materials Laboratory. The housing and internal parts were dry and covered with fine metallic particles and soot, with no evidence of lubricating oil or fluid. Gears and bearings showed heat damage and deformation; the pinion displayed severe heat and wear damage. A flashlight aimed at the oil level sight glass transmitted no light, indicating the sight glass was opaque.
Maintenance History
Review of maintenance records revealed that the 90° gearbox had been installed on the accident helicopter on October 23, 2007, at an airframe time of 8,412 hours. At the time of the accident, the gearbox had 260.9 hours since overhaul. The gearbox complied with FAA Airworthiness Directive 90-10-05, dated June 5, 1990, which addressed tail rotor gearbox duplex bearing failure prevention. On February 15, 2022 (23 days after the accident), the gearbox was removed for examination, showing an airframe time of 9,025.8 hours and a gearbox total of 3,124.5 historical hours, with 298.9 hours since overhaul.