Accident Overview
On September 10, 2022, at approximately 1550, a Bell 206L-1 helicopter, registration N242BH, was substantially damaged during an accident near Banning, California. The pilot and two passengers sustained minor injuries. The helicopter was operating under Title 14 Code of Federal Regulations Part 91 as a firefighting flight, contracted by the California Department of Forestry and Fire Protection (Cal Fire).
Sequence of Events
The pilot was transporting two Cal Fire employees to Banning Municipal Airport. During final approach, the helicopter experienced an uncommanded right yaw about the vertical axis. The yaw increased despite the pilot applying full left pedal. The pilot announced to passengers that he suspected a loss of tail rotor. At an altitude of approximately 100 to 150 feet above ground level, he chose not to autorotate due to the presence of people and aircraft below, maintaining low power and airspeed. After the helicopter turned about 180°, the pilot identified a backyard landing area and maneuvered toward it. At about 50 feet agl, the helicopter continued a continuous right rotation despite full left pedal. The pilot applied collective to cushion the landing; the helicopter landed hard, bounced, and rolled onto its left side. Multiple witnesses reported the helicopter spinning before descending. The pilot shut off the fuel and exited with assistance from first responders. One passenger exited unassisted and helped the other passenger exit.
Examination and Findings
Postaccident photographs provided by the pilot showed substantial damage to the main rotor assembly, fuselage, and tailboom. All major components were identified near the main wreckage except fragments of the main rotor blades found on a nearby street. The tail rotor drive shaft had separated from the air conditioner pulley flange at the flex coupling. Two bolt shank fragments with attached nuts were found trapped in the holes of the pulley flange. A bolt head piece, a nut, and six washers were recovered from the enclosed area. Neither the drive ring nor most of the connecting hardware were recovered despite a thorough search.
Examination of the separated components at the NTSB Materials Laboratory revealed that one end of the drive shaft had a complete and intact flex coupling, while the other end had a separated flex coupling. Fracture surfaces on the bolt pieces trapped in the pulley flange exhibited relatively flat features with curving crack arrest lines, consistent with fatigue fractures. The trapped nut end of one bolt was mated to the recovered head piece; the total bolt shank length between clamping faces measured 0.494 inch. The pulley flange thickness was 0.164 inch, and the drive shaft flange thickness was 0.161 inch. For reference, the drive ring thickness on the intact coupling was 0.119 inch. The six recovered washers included four 0.058-inch-thick and two 0.029-inch-thick washers, while the specified washers for the pulley flange to drive ring assembly include one 0.032-inch and three 0.063-inch washers.
Review of maintenance records indicated no recent work to the tail rotor drive shaft or air conditioning unit, and no anomalies were noted.
Damage
The helicopter sustained substantial damage to the main rotor assembly, fuselage, tailboom, and main rotor blades.