History of Flight
On July 11, 2016, at 1123 central daylight time, a Bell 407 helicopter, registration N427TV, collided with terrain while on approach to land at the Tennessee Valley Authority (TVA) Mayfield Customer Service Center in Hickory, Kentucky. The commercial pilot was fatally injured, and the helicopter sustained substantial damage from impact forces. The helicopter was registered to and operated by the TVA under 14 Code of Federal Regulations Part 91 as a business flight. Day visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from Outlaw Field Airport (CKV) in Clarksville, Tennessee, at 1048.
According to TVA personnel, the pilot had flown from Knoxville, Tennessee, to CKV, refueled, and then proceeded to the TVA Customer Service Center to pick up a maintenance lineman for inspecting power lines and equipment.
Witness Account
A TVA lineman who witnessed the accident reported light wind from the south/southeast and observed the helicopter making a final approach from the north. He noted no abnormalities in sound or position until the helicopter was about 75 to 100 feet above the ground. At that point, he saw the main rotor abruptly tilt to the right, followed by the helicopter banking right, falling to the ground, and coming to rest on its right side. The witness stated he never lost sight of the helicopter, described the impact as very hard with no sliding or bouncing, and saw the rotor blades break apart. He then ran to the building for help. The helicopter's engine continued running after the accident and was shut down by responding personnel.
Aircraft and Maintenance Information
The helicopter was a Bell Helicopter model 407, serial number 54106, built in 2012 and purchased new by the TVA. It was a single-engine helicopter with a four-blade main rotor system, a full monocoque aluminum-skinned tail boom, and a conventional two-blade tail rotor. It was powered by a Rolls-Royce model 250-C47B turboshaft engine.
The helicopter was issued a normal category standard airworthiness certificate and maintained under an approved aircraft inspection program. Between May 31, 2016, and June 20, 2016, it underwent multiple inspections at the TVA maintenance facility in Muscle Shoals, Alabama. From June 20 until the accident, it operated about 38.4 hours.
The collective lever, located at the front and bottom of the swashplate support, was attached to the pivot sleeve with screws, washers, and pivot pins. Lock wire was typically affixed after applying specified torque. The maintenance tasks performed during the inspections did not require removal or inspection of the collective lever pins or screws. An inspection of flight control bolts and nuts was performed, but this did not include the collective lever pins.
Personnel and Interviews
Maintenance and inspections of flight controls were performed by two TVA airframe and powerplant mechanics and a TVA foreman. All were interviewed by FAA inspectors. One mechanic re-installed an anti-drive lever assembly but did not recall removing lockwire or pins on the collective lever. The other mechanic performed the 24-month inspection of flight control bolts and nuts and did not remember removing the collective lever pins. The foreman stated that removal of the collective lever pins was not part of required maintenance, and he was unaware of any removal or lockwire removal. He noted that it could have been done voluntarily during the 24-month bolt inspection. Both mechanics mentioned being occasionally pulled off aircraft for other work, and one noted a lack of documentation of parts removed.
Examination Findings
Initial wreckage examination revealed that the collective lever connecting the cockpit collective controls to the main rotor was disconnected from the pivot sleeve. Attaching hardware (two pivot pins and screws) was found loose in the wreckage: on the transmission deck and on the ground under the right side. Flat washers and lockwire were missing; washers were later found. The pins and screws showed no thread stripping. No lockwire was attached at the screw heads. One washer showed circumferential scoring; one screw had flattened thread peaks consistent with partial insertion.
The helicopter came to rest on its right side about 220 feet west of the intended landing zone, a level gravel area. All four main rotor blades separated; tail boom aft section severed; tail rotor remained attached. The engine showed no pre-impact anomalies. The FADEC ECU recorded low rotor speed (below 92%) as the initial trigger, and data revealed no engine anomalies before impact.
Weather Information
The nearest official weather station, Mayfield-Graves County Airport (M25), 8 miles away, reported at 1135: wind from 120° at 5 knots, visibility 10 statute miles, scattered clouds at 1,000 and 2,200 ft, overcast at 10,000 ft, temperature 26°C, dew point 22°C, altimeter 30.06 inHg.
Medical and Pathological Information
The Office of the Chief Medical Examiner of Kentucky performed an autopsy. The cause of death was blunt impact injuries of the head, neck, and torso with traumatic/positional asphyxia; manner of death was accident. FAA toxicology tested negative for carbon monoxide, ethanol, and major drugs of abuse.
Survival Aspects
The helicopter's front seats had 4-point restraints. The pilot's outboard lap belt attachment point separated from the airframe; rivets were pulled through or sheared. The pilot was not wearing a helmet, and helmets were not required or provided by TVA.
Post-Accident Actions
Following the accident, the operator implemented several safety initiatives, including two independent safety audits, a formal fatigue risk management program, a safety management system, a formal tool/material accountability program, new work interruption policies, a formally-trained safety officer position, and a formal process for communicating safety-critical information.