History of Flight
On August 1, 2021, at approximately 1251 Pacific daylight time, a Robinson Helicopter Company R66, registration N7000J, was substantially damaged when it impacted terrain near Colusa, California. The pilot and three passengers sustained fatal injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
According to automatic dependent surveillance-broadcast (ADS-B) data from the Federal Aviation Administration, the helicopter departed Willows, California, around 1207. It flew toward the foothills bordering the western edge of the valley, then turned south while over Elk Creek. The aircraft overflew Lodoga and Stonyford before turning east. After about 12 minutes on an easterly heading, it turned to a southeasterly heading for approximately two minutes, then initiated a left turn back to east when about 0.7 miles west of the accident site. The last ADS-B data point placed the helicopter 392 feet west of the crash location. No altitude information was recorded.
A witness driving south on a highway about 0.5 miles east of the accident site reported seeing the helicopter flying east at 50 to 100 feet above ground level. Initially straight and level, the helicopter suddenly made a sharp left turn. The witness briefly lost sight due to trees; upon regaining visual contact, he observed the helicopter sharply diving, followed by impact with the ground.
Aircraft Information
Review of the helicopter's airframe and engine logbooks indicated that at the time of the most recent annual inspection, the Hobbs meter, airframe total time, and engine total time were all 378.2 hours. The helicopter was not equipped with onboard devices that recorded airspeed, altitude, yaw, pitch, roll, or flight control positions.
Wreckage and Impact Information
Examination revealed the helicopter impacted a tomato field. Debris was scattered across an area measuring 360 feet by 392 feet. A portion of the main rotor blade lay on the western edge of the debris field. The right door was found about 161 feet southeast of that blade portion. About 112 feet south of the door, the outboard portion of one blade was located. A U-shaped ground impression, 16 feet long and 8 inches wide, was found about 8 feet east of that outboard blade section. The main rotor gearbox and assembly were discovered about 5 feet east of the impression.
The forward left and right control tubes, along with their servos and the servo mount structure, were located about 3 feet west of the main wreckage. The engine had separated from the fuselage and lay adjacent to it.
The airframe showed a dent on the lower windshield frame at the forward lower right, consistent with the size and shape of a main rotor blade leading edge. The aft fuselage exhibited buckling, compression, and crushing. The cabin area had separated behind the forward seatbacks and was tethered by wires. The tailcone separated at its forward end, and the empennage separated from the tailcone. The driveshaft from the engine to the gearbox separated near the engine, with twisting and torsional fractures.
Cyclic and collective control continuity was established, but multiple separations consistent with overload were found throughout. The attachment hardware for the forward left and right control tubes at the nonrotating swashplate was not located at the site or within recovered wreckage. The three control tubes from the servo to the swashplate remained intact, with slight bends and scratches.
Tail rotor controls were separated in multiple areas, all consistent with impact damage or overload. Main rotor blades showed varying degrees of damage and fractures.
The engine had separated from the airframe; the turbine module and fuel control unit were fractured and separated from the gearbox. N1 and N2 rotated freely by hand. The upper magnetic chip detector was free of ferrous debris; the lower detector was not located.
Disassembly of the turbine module revealed the gas generator turbine rotated freely, while the power turbine was locked due to impact damage. The second, third, and fourth stage turbine airfoils were intact and undamaged. Data downloaded from the engine monitoring unit showed the engine was operating at the time of the accident. No evidence of pre-existing mechanical anomalies was noted.
The main rotor mast assembly, swashplate assembly, flight control servos, upper push-pull tube assemblies, and mast fairing ribs were sent to the NTSB Materials Laboratory for further examination.
The main rotor mast was bent aft. Pitch change links were fractured on slant planes consistent with ductile overstress. The tube assembly attached to the mast fairing upper rib had separated at a riveted joint; rivets on the forward side were sheared, and the tube above was rotated aft. Left and right upper flight control push-pull tubes were bent, and fasteners attaching them to the lower swashplate assembly were missing. On the control servos, pieces of lower push-pull tubes remained attached, with fractures on slant planes consistent with ductile overstress. Mounting frame pieces also had ductile overstress fractures. Mast fairing ribs were deformed, with contact damage at the edges of through-holes for the flight control upper push-pull tubes.
The forward left and right control attachment lugs on the swashplate were cleaned and examined. No substantial thread imprints were observed in the attachment holes. Remnants shaved from the attachment bolt were located on the lower forward half of the left-side hole, and the area between bolt remnants was rubbed. Examination of the lower portion of the bolt remnant with a scanning electron microscope revealed dimple features consistent with ductile overstress fracture.
Additional Information
The FAA’s Helicopter Flying Handbook contains information on low-G conditions and mast bumping, noting that helicopters with two-bladed teetering rotors rely entirely on thrust vector tilt for control, and low-G conditions can be catastrophic. It describes the dangers of abrupt forward cyclic input or pushover, particularly at higher speeds, and explains how improper corrective action may lead to mast contact with the rotor mast, known as mast bumping.