ERA16FA248

Company maintenance personnel's inappropriate removal without replacement of the safety wires on the collective lever pin screws during a recent maintenance inspection, which resulted in the screws backing out and led to a loss of collective control in flight.

The pilot was performing a visual approach to a landing zone to board an additional crewmember. A witness reported that there were no abnormalities in the helicopter's sound or position, until it was approximately 75 to 100 feet above the ground. Suddenly, the main rotor tilted to the right. Immediately after, the entire helicopter banked to its right and fell to the ground on its right side, where it came to rest. The main rotor blades broke apart during the impact sequence. The engine continued to run after the accident, and was subsequently shut down by responding personnel. An examination of the wreckage revealed that the collective lever, located at the front and bottom of the swashplate support, was disconnected from the pivot sleeve. The collective lever was designed to move the pivot sleeve vertically on the swashplate support, via direct linkage from the cockpit collective control, to change the pitch on all the main rotor blades simultaneously. The collective lever pins and screws that attached the collective lever to the pivot sleeve were missing; they were later found loose, near the main rotor area. The safety wires intended to secure the screws to the pins were missing. Examination of the hardware at the NTSB Materials Laboratory revealed that the safety wires not present, and the screws backed out over time, resulting in the complete loss of collective control in flight. Maintenance on the helicopter was performed about 38 flight hours prior to the accident. The maintenance included a 24-month inspection that required examination of the flight control bolts and nuts. The collective lever pins were not specifically included in that inspection. Two mechanics and a maintenance foreman, all employees of the operator, performed the maintenance, and all reported during postaccident interviews that they did not recall removing the safety wire or examining the pins. However, the foreman added, "I could see why it [examination of the collective lever pins] could have been done. The 24-month flight control bolt inspection was being performed, why not pull them and look at them too. I've done it before." Two of the mechanics reported that they would occasionally be "pulled off" one aircraft to work on another, and there was no work interruption policy in place. Thus, given that the safety wires were missing, it is likely that they were removed and not replaced during the most recent maintenance and that maintenance personnel did not recall taking that action due to possible work interruptions. Subsequent to the accident, the operator implemented numerous safety initiatives to prevent recurrence, 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, creation of a formally-trained Safety Officer position, and a formal process for the communication of safety-critical information.

The helicopter's front seats were equipped with 4-point restraints. The outboard (right side) restraint attachment point for the pilot's lap belt was separated from the airframe wall. The rivets were pulled through and attached on one side, and the rivets were sheared on the other side. The sheared rivets were not located; however, the rivet holes were elongated from shear forces. The pilot was not wearing a helmet at the time of the accident, nor were helmets required or provided for helicopter operations at the TVA. The collective lever and attachment hardware were sent to the NTSB Materials Laboratory for further examination. The collective lever, collective lever pins, collective lever pin screws, and washers were examined visually and by optical microscopy. All components were intact. Threads on the collective lever pin screws and the mating threaded holes in the collective lever were intact with no evidence of stripping. Holes for attaching lockwire were present in the heads of the screws and at an adjacent area on the collective lever, but no lockwire was observed attached at either location. Deformation at the edges of the lockwire holes was noted. Circumferential scoring was present across the entire face on one side of one of the washers. On one of the screws, thread peaks were flattened near the middle of the shank on one side of the screw consistent with contact with the collective lever pin hole bore with the screw partially threaded into place. Subsequent to the accident, the operator implemented numerous safety initiatives to prevent recurrence, 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, creation of a formally-trained safety officer position, and a formal process for the communication of safety-critical information. Mayfield - Graves County Airport (M25), Mayfield, Kentucky, was the closest official weather station, which was 8 miles from the accident location. The M25 weather at 1135 included wind from 120° at 5 knots, visibility 10 statute miles, scattered clouds at 1,000 and 2,200 ft, overcast ceiling at 10,000 ft, temperature 26°C, dew point 22°C, and altimeter setting 30.06 inches of Mercury. The Office of the Chief Medical Examiner, Commonwealth of Kentucky, Louisville, Kentucky, performed an autopsy of the pilot. The cause of death was blunt impact injuries of the head, neck, and torso with traumatic/positional asphyxia, and the manner of death was accident. The FAA's Bioaeronautical Research Sciences Laboratory performed toxicology testing on specimens from the pilot. The specimens tested negative for carbon monoxide, ethanol, and major drugs of abuse. The pilot, who was seated in the right cockpit seat, held a Federal Aviation Administration (FAA) commercial pilot certificate with airplane single-engine land, rotorcraft-helicopter, instrument airplane, and instrument helicopter ratings. He held an FAA second-class medical certificate with a restriction to wear corrective lenses. The pilot reported 18,430 total hours of flying experience on his latest medical certificate application, which was dated March 31, 2016. TVA personnel reported that his flight experience in the Bell 407 was about 850 hours. He completed a flight review in a MD Helicopters MD530 helicopter on February 12, 2016, and a flight review in the Bell 407 on January 5, 2016. 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 of conventional construction and equipped with a four-blade, soft-in-plane design, composite hub, main rotor system, a full monocoque aluminum-skinned tail boom, and a conventional two-blade tail rotor system. The helicopter was powered by a Rolls-Royce model 250-C47B turboshaft engine, serial number CAE-848434, with maximum takeoff and maximum continuous power ratings of 650 and 600 shaft horsepower, respectively. The helicopter was issued a normal category standard airworthiness certificate and was maintained under an approved aircraft inspection program. Between May 31, 2016, and June 20, 2016, the helicopter was at the TVA maintenance facility at Muscle Shoals, Alabama, and the following inspections were accomplished: annual/50hr/100 hr, 150hr, 300 hr, 300hr/12 month, 600hr/12 month, 1200 hr/2 year, 12-month and 24-month inspections. From June 20, 2016, until the time of the accident, the helicopter was operated about 38.4 hours. The collective lever was located at the front and bottom of the swashplate support. The collective lever and collective control link were designed to move the pivot sleeve vertically on the swashplate support to change the pitch on all the main rotor blades simultaneously. The collective lever was attached to the pivot sleeve with screws, washers, and pivot pins (see figure 1). Once attached, the and the specified torque was applied, locking wire would typically be affixed to the screw. Figure 1 - Swashplate support assembly, with collective pitch lever attaching hardware outlined in red. The maintenance tasks performed during the inspections between May 31, 2016, and June 20, 2016, did not require the removal of the collective lever or the disconnection or inspection of the collective lever pins or screws. Although an inspection of the condition of the flight control bolts and nuts was one of the maintenance tasks performed, an inspection of the collective lever pins, screws, and corresponding lockwire was not included in that inspection. The maintenance and inspections of the helicopter's flight controls, including the collective control, were performed by two TVA airframe and powerplant mechanics and one TVA foreman, who assisted in the work and supervised the operation. All three employees were interviewed by FAA inspectors following the accident. One of the mechanics re-installed an anti-drive lever assembly. He did not recall removing the lockwire on the collective lever pin screws or removing the pins. He stated that the other mechanic performed the 24-month inspection of the flight control bolts and nuts. He further stated that the collective lever pins were not part of that inspection. The other mechanic performed the 24-month inspection of the flight control bolts and nuts. When asked if he removed the collective lever pins, he responded, "No, I don't remember doing it. If anyone would have done it, it would have been me, but I don't remember doing it." The foreman inspected the work performed in the area of the flight controls. He reported that the removal of the collective lever pins "…was not part of the required maintenance performed." He was not aware that the pins were removed or that any lockwire was removed. He added further, "I could see why it could have been done. The 24-month flight control bolt inspection was being performed, why not pull them and look at them too. I've done it before." Both mechanics reported that they would occasionally be "pulled off" an aircraft to perform work on another project. One mechanic stated that there was a lack of documentation of what parts were removed, such as a continuation sheet. General The helicopter came to rest on its right side, about 220 ft west of the intended landing zone (LZ). The LZ was a level, open, gravel-covered storage area for power transmission equipment. All four main rotor blades separated from the main rotor hub during the impact sequence. The aft section of the tail boom severed from the fuselage, and the tail rotor assembly remained attached to the aft section of the tail boom. Fuel and Hydraulic Systems The helicopter's fuel system was not compromised and contained about 695 pounds of fuel. No fuel leaks were observed, and all fuel hoses and lines were secure. The airframe-mounted fuel filter was clean, and the fuel inside was cl