N36FABell OH-58A · 1968

On February 6, 2023, about 2140 mountain standard time, a Bell OH-58A helicopter, N36FA, was substantially damaged when it was involved in an accident near Yuma, Arizona. The commercial pilot sustained minor injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight.

The pilot stated that he landed in night conditions on the load truck and the chemical hopper was filled with 50 gallons of water to rinse out the applicator system. The pilot departed from the load truck toward an open field about 200 yards away. While maneuvering about 40 ft above ground level, with a speed near effective translational lift, and about 80% transmission torque, the helicopter suddenly started to bounce and yaw. The pilot stated that, when the spray tank was almost empty, the helicopter began to “bounce and tilt in all directions,” then “fish-tailed” before the engine lost total power. The pilot arrested the helicopter’s forward movement by pulling back on the control stick and leveled the helicopter while lowering the collective. Unable to judge his height above the ground, the pilot alternately raised and lowered the collective to control the descent, and the helicopter landed hard in the dirt field, and a main rotor blade struck and severed the tail rotor driveshaft. The main rotor and blades assembly separated from the mast and landed about 100 ft from the upright helicopter, as shown in Figure 1.

Figure 1 - Main rotor yoke and blades (Photo courtesy of operator)

The airframe had accrued a total of 9,629.8 hours at the time of the accident; its most recent annual inspection was 8 months before the accident. Flight control continuity was established from the cyclic and collective control to the hydraulic servos and from the hydraulic servos to the non-rotating swashplate. Flight control continuity was established from the anti-torque pedals to the tail rotor pitch control rods. Continuity was established from the throttle twist grip to the fuel control, and from the collective to the fuel governor. The master fuel valve lever was observed in the ON position. Fuel was present from the airframe filter to the fuel spray nozzle. A visual assessment of the fuel remaining found approximately 5 gallons of clean and clear fuel in the fuel tank. The fuel quantity gauge, when energized, did not display an accurate depiction of the actual amount of fuel on board, registering near zero. The fuel supply hose from the airframe fuel filter canister to the engine fuel pump inlet was removed. Fuel dripped from the engine fuel pump after the hose was removed. The fuel pump was found operable when power was applied to it. A general visual inspection of the engine’s various fuel, oil, air, and electrical connections, including B-nuts, indicated that they were tight and painted with torque stripe.

The helicopter was powered by an Allison M250-C20C (T-63-A720), a turbo-shaft, gas-coupled free-power turbine engine. The most recent engine replacement was annotated in the engine logbook and was completed on October 18, 2022, about 4 months before the accident flight. The most recent 100-hour inspection was completed on December 27, 2022, at an aircraft total time of 9,573.8 hours. During a postaccident test run, the engine produced sufficient power and revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.