ERA14FA396

An inadvertent collision with a utility wire for reasons that could not be determined from recorded data and examination of the helicopter and accident site.

The pilot and passenger were inspecting a span of high-tension powerlines for damage after a recent storm. Recorded data showed that the helicopter departed and proceeded along the left side of the span at an altitude roughly consistent with the height of the suspended wires. The helicopter's last recorded position was about 400 ft laterally and about 25 ft below the point where it ultimately contacted and severed the uppermost wire of the span, which was about 150 ft above ground level. The severed wire was located on the right side of the span, whereas the helicopter was flying on the left. The helicopter's ground track transitioned from left to right and back across the span near transmission towers earlier during the flight; however, there were no transmission towers located in the immediate vicinity of the accident site. Portions of the wreckage came to rest directly below the severed wire, and oriented along a debris path to the right of and along the helicopter's previous direction of travel. Examination of the wreckage revealed no evidence of any mechanical malfunctions or failures before the helicopter contacted the wire.

A handheld GPS receiver was recovered from the wreckage and forwarded to the NTSB Vehicle Recorder Laboratory for examination and data recovery. The unit sustained major impact damage to the screen and casing. The memory chip was located after an interior inspection and a chip-level recovery was performed. The data were successfully obtained from the memory chip. The accident flight was identified by 181 data points spanning between 1030:46 and 1100:46, with one data point recorded every 10 seconds. According to the data, the helicopter departed from TCL at 1034 and proceeded east before intercepting the north/south oriented powerline span about 1040, and proceeding north. The helicopter maintained approximate GPS groundspeeds between 30 and 60 knots, GPS altitudes between 300 and 700 feet, and generally flew on the west (left) side of the powerlines. The ground track briefly slowed and transitioned to the east (right) of the powerlines on two occasions, about 1047 and 1058. Both of the transitions occurred roughly at points along the powerlines where transmission towers were present. At 1100:26, the calculated GPS groundspeed was 32 knots, and the GPS altitude was 467 feet, or about 120 feet agl. The next recorded position, at 1100:36, placed the helicopter at 33 knots GPS groundspeed, 522 feet GPS altitude, and about 125 feet agl. The final recorded position, at 1100:46, recorded a GPS groundspeed of 32 knots, 537 feet GPS altitude, or about 164 feet agl. This position was roughly 410 feet north of transmission tower 82. The helicopter's tail rotor was recovered about 400 feet northeast of the final recorded GPS position. Figure 1 – Accident Site Diagram Depicting GPS Flight Path and Helicopter Wreckage An autopsy was performed on the pilot by the Alabama Department of Forensic Sciences, Montgomery, Alabama. The medical examiner determined that the cause of death was multiple blunt force injuries. Toxicological testing performed by the FAA's Civil Aerospace Medical Institute found no trace of ethanol or other drugs present in the samples submitted for the pilot. The accident site was located along the eastern edge of the powerline easement, which was oriented roughly north-south along uneven terrain in a shallow valley between two transmission towers. The transmission towers were identified as 81 and 82, and were located north and south of the accident site, respectively. A 6-gauge, 3-strand aluminum shield wire about 0.35 inches in diameter, which spanned between the two towers on their eastern side, was severed about 775 feet north of tower 82. The shield wire's estimated height above ground level at that point along the span was about 150 feet. The remaining fiber optic cable and three power transmission phase cables appeared undamaged. The helicopter fuselage came to rest inverted within a creek bed, just outside and east of the easement, in a forested area. The helicopter's static mast, main rotor hub, and four of the five main rotor blades were separated from the fuselage, along with the aft portion of the tailboom. The remaining main rotor blade separated from the main rotor hub at the strap pack. The main rotor blades exhibited extensive damage which varied in severity and included fractures, gouges, bent spars, cord-wise wrinkling, leading/ trailing edge damage, bending, separation and indications of a wire strike. All of the separated components were located within about 90 feet of the fuselage, and in the general vicinity of the severed shield wire, with the aft portion of the tailboom coming to rest nearly directly below the break point of the shield wire. The wreckage displayed no evidence of a pre- or post-impact fire. The helicopter exhibited extensive damage to the main airframe structural members, static mast support structure and center beam. The static mast was separated at the mast base by fractures near the mast base attachment points. The forward fuselage, including the door and canopy frames, cockpit, and instrument panel were also damaged. All of the canopy windscreens were broken. The cockpit compartment was compromised from ground impact. Both sides of the cockpit and cabin floors were crushed, bent and distorted. Examination of the cockpit seat belts and shoulder harnesses revealed that they functioned normally. All cockpit and cabin doors were installed, and a single set of flight controls was installed at the pilot's position in the left front seat. The pilot was wearing a helmet. The aft boom fairing exhibited crushed, dented and torn exterior skin surfaces. The air inlet fairing was separated near its mounting base, and exhibited relatively uniform separation surfaces on both of the separated portions. The tailboom was fractured into three pieces, with the first fractured near fuselage station (FS) 200, in the area of the FS 197 mounting frame, with no apparent damage to the mounting bolts. The second section was fractured around FS 258, and exhibited concave depressions consistent in size with the main rotor profile. The third section contained the tail rotor gearbox, tail rotor assembly, vertical and horizontal stabilizers. The horizontal stabilizer and vertical stabilizers sustained various degrees of impact damage to the frame structures, leading edges and exterior skin surfaces. There was no visible indication that the shield wire made contact with the tailboom, empennage, tail rotor, or either of the helicopter's two installed wire strike protection devices. The main transmission rotated freely, contained oil, and the chip detectors were inspected and found clean of magnetic particles. Drive continuity from the transmission to the tail rotor output pinion was present. The main rotor transmission mounting points had visible damage to the main transmission housing mounting bores and mounting studs. The main rotor transmission output splines and mating splines on the main rotor driveshaft were visibly damaged from the separation of the main rotor static mast. The engine-to-transmission drive shaft had fractured in apparent overload. The shaft fractured immediately forward of the aft flexible coupling. The coupling exhibited bending damage, but remained intact. The over-running clutch operated normally. The oil cooler blower assembly mounting bracket and scroll was impact-damaged. The tail rotor gearbox and tail rotor assembly appeared undamaged. The gearbox was mounted securely to the FS 281 frame, contained oil, and rotated freely. There were no metallic chips on the chip detector. The tail rotor swashplate rotated smoothly. The tail rotor driveshaft fractures corresponded to the damaged tailboom. Both the forward and aft tail rotor driveshaft couplings appeared undamaged. The tail rotor blades, pitch links, hub, fork, fork bolt and elastomeric teetering bearings appeared undamaged. There were fractures, bends and distortion throughout the flight controls. Control continuity was verified for the collective, cyclic and tail rotor controls with all control discontinuities displaying impact-related damage consistent with overload separation. The pilot's cockpit controls and under the seat routed controls were extensively damaged. The lateral and longitudinal actuators were removed and inspected. Both actuator shafts were found near the approximate mid-points of their travel. Damage and fractures to the upper controls including the control rods, pitch links, rotating and stationary swashplates displayed signatures consistent with overload separation. The engine remained inside its cowling and all but the right forward engine mounts were fractured. The engine compressor exhibited foreign object damage consistent with ingestion of small, hard-body and soft-body foreign objects during engine operation. Wood debris, pine needles and leaves were ingested deep into the compressor. Most compressor blades exhibited leading edge impact marks and bending in the opposite direction of no