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On October 30, 2010, about 1030 eastern daylight time, an MD Helicopters, Inc. 369E, N765WH, operated by Winco, Inc., was substantially damaged when it collided with power transmission wires and terrain while performing external-load/line-maintenance operations near Thomas, West Virginia. The certificated commercial pilot was seriously injured. Of the three linemen on board, two suffered minor injuries while one was fatally injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local external load flight, which was conducted under the provisions of 14 Code of Federal Regulations Part 133.
The pilot and both surviving linemen recounted a similar series of events during separate post-accident interviews.
On the day of the accident, the helicopter was tasked with transporting four linemen between several power transmission towers so that they could transfer fiber optic grounding lines from pulleys used during their installation, to their final fixed location on the tower. The crew began their work at 0820 that morning by transporting two of the linemen to transmission tower number 242, and had progressed sequentially, my moving groups of two linemen at a time, to the final tower for this portion of the operation, number 248.
On each of the seven towers worked on that day, the same procedure was used to drop off the lineman to perform the work. The helicopter hovered near the transmission tower's peak, while the linemen disembarked the helicopter, then after the helicopter ascended vertically approximately 40 feet, the linemen retrieved their equipment from the end of a sling suspended 40 feet below the helicopter, and then began their work. When the work was complete, the lineman would call the helicopter via radio, and it would return to pick up the linemen and their equipment using the exact opposite procedure. The linemen would first load their equipment onto the sling, and then the helicopter would descend so that the linemen could re-board the helicopter while it hovered adjacent to the transmission tower's peak, about 100 feet above ground level. The procedure of transferring the linemen and their tools to or from a transmission tower had been executed 32 times on the day of the accident flight. These operations were conducted identically each time, with the exception of the third lineman that was carried on the accident flight. The accident flight was to be the final transfer of the day.
Two linemen were assigned to each tower, but one of the linemen was having difficulty finishing his work on tower 248, so the helicopter transported another lineman to the tower to assist him. After all three linemen had completed their work on tower 248, the helicopter returned to retrieve them and their equipment. While moving from tower to tower, the lineman were either seated in the helicopter or tethered to the helicopter while standing on the helicopter's left skid. Their equipment was then carried at the end of a 40-foot sling suspended below the helicopter.
After the lineman who was located at the north peak of tower 248 completed his work, his equipment was loaded on to a three prong grappling hook, suspended from the bottom of the sling, then the helicopter descended and the lineman boarded the helicopter. The pilot then climbed the helicopter vertically, cleared the suspended load from the tower, and positioned the helicopter 40 feet above the peak on the south side of the tower. After loading the linemen’s equipment the helicopter descended to the peak to pick up the two linemen from that peak. Two of the linemen were seated in the rear of the helicopter, while the third lineman was standing on the helicopter's left skid.
The pilot stated that after the linemen boarded, he "cleared" the tower and moved the helicopter forward. He could not recall the helicopter's altitude above the tower, but remembered that the helicopter began "shaking with a large vibration." He struggled with the cyclic control, felt the helicopter "hit something" before it began "spinning." He remembered pulling up on the collective pitch, impacting the ground, and then moving the throttle to the "off" position.
According to one of the linemen, after all three had boarded, "…the helicopter pulled away [from the tower]. The whole helicopter then paused and after that started shaking prior to impacting the ground." The other lineman stated that instead of backing up and away from the tower as he expected, the pilot "picked up and powered into it." The lineman further stated that he felt a "pause" and the engine "bogged down."
During the impact sequence, one of the linemen, who was sitting in the helicopter but not tethered to it, was thrown clear and sustained minor injuries. The other surviving lineman was also seated in the aft cabin of the helicopter, but remained tethered to the safety hook, and also sustained minor injuries. The lineman standing on the helicopters skid, who was also tethered to the safety hook, was fatally injured during the impact sequence.
When asked, the pilot could not recall attempting to jettison the external load at any point during the accident sequence.
According to records provided by the operator, the pilot held a commercial pilot certificate with a rating for rotorcraft-helicopter. The pilot had accumulated 1,682 total hours of flight experience, all of which were in rotorcraft, and 282 hours of which were in the accident helicopter make and model. The pilot's most recent FAA second-class medical certificate was issued on February 15, 2010, with the limitation "must wear corrective lenses."
According to training records provided by the operator, the pilot was hired in March 2010, and reported previous experience operating turbine-powered helicopters and operating with external loads. The pilot completed 4.6 hours of external load and vertical reference training at a third party facility on April 28, 2010. Once employed by the operator, the pilot completed 18.7 flight hours of “initial training”. Over the next six months the pilot received 434.7 flight hours of “on the job training” with more experienced company pilots, including 126.5 flight hours performing the operation that was being performed at the time of the accident. On October 27, 2010, the pilot was certified by the operator as proficient in operations that included: approach to, operations at, and departure from a structure; approach to, transfer lineman on/off, and departure from a structure, and helicopter external load operations.
According to maintenance records supplied by the operator, the helicopter was manufactured in 2009 and its airworthiness certificate was issued on December 7, 2009. The helicopter's most recent 100 hour inspection was completed on October 23, 2010 at 392 total helicopter hours.
The helicopter was equipped with several mission-related modifications for the performance of power line construction/maintenance. These modifications included (but were not limited to), a safety harness attachment point on the left side of the helicopter for the linemen, a deck plate to facilitate boarding the helicopter, and an external cargo hook. The cargo hook featured electric and manual release systems, both of which were located on the cyclic control. A 40-foot synthetic fiber-rope sling (red in color) attached to the cargo hook was used to ferry the linemen's equipment from site to site. The sling was equipped with a custom-made, 3-prong grappling hook, which was fabricated by the operator.
At 1051 the weather reported at Elkins-Randolph County Airport (EKN), located 24 nautical miles southwest of the accident site, included clear skies, 10 statute miles visibility, calm winds, temperature 5 degrees C, dewpoint 0 degrees C, and an altimeter setting of 30.13 inches of mercury.
The pilot stated that the weather at the accident site included calm winds, with no gusts or crosswinds. The temperature was "cold" and the sky was "sunny."
WRECKAGE AND IMPACT INFORMATION
The helicopter, its associated components, with cargo sling attached came to rest on the west side of tower 248. A broken section of sling with grappling hook and lineman equipment attached came to rest near the southeast corner of the tower's base. Terrain elevation at the base of the tower was 2,598 feet, and the tower was 100 feet-tall. The power transmission lines were arranged along the top of the tower in three groups of three conductors each. The distance between each of the three individual conductors was 14 inches. Grounding fibers were located at the north and south peaks of the towers. All of the transmission lines and both grounding fibers were suspended from the tower in roughly an east-west orientation.
The fuselage of the helicopter came to rest about 100 feet west of the transmission tower, lying on its left side and oriented 360 degrees magnetic. The tail boom was separated from the fuselage at a point about 2 feet forward of the tail rotor gearbox. The separated portion of the tail, which included the intact tail-rotor was found 58 feet west of the tower, between the tower and the fuselage.
The vertical stabilizer exhibited two parallel concave depressions, located about 14 inches apart. Contact marks consistent in size and orientation of the transmission line wire strands were observed along the interior of both depressions. Both tail rotor blades exhibited concave depressions that roughly corresponded to the position of the lower most contact mark on the vertical stabilizer and also exhibited similar wire contact signatures. Examination of all three conductors grouped near the middle of the tower revealed contact marks exhibiting damage and paint transfer consistent with contact between the conductors and both the vertical stabilizer and tail rotor blades. The tip of one tail-rotor blade was separated, and found about 100 feet north of the tail rotor.
All five main rotor blade grips were separated from the main rotor hub at the strap packs, and each main rotor blade was further separated from its respective blade grip at the root. The main rotor blades were distributed about the accident scene in an arc that ranged from the southwest to northwest of the fuselage. All of the blades exhibited signatures consistent with ground contact, and one blade was broken into three roughly equal portions.
Control continuity was traced from the flight controls to the cyclic and collective pitch links, pitch housings, and main rotor blade straps, which were fractured at the main rotor hub. The scissors link was fractured through the mid-section and the rotating swashplate and scissors crank were not fractured. No damage was noted to the secondary swashplate. The rotating swashplate was removed and the swashplate bearing and spherical bearing inspected. The swashplate's spherical bearing was free to move vertically about 0.016-inch. There was no evidence of rotation between the spherical bearing race and the double row ball bearing race.
Tail rotor control continuity was traced from the control pedals through the fracture in the tail boom, to the tail rotor pitch change links, which remained attached to the tail-rotor. Main rotor drive continuity was verified from the engine N2 and overriding clutch to the main rotor. Tail rotor drive continuity was verified from the main transmission through four fractures in the tail rotor driveshaft to the tail rotor gearbox. The aft-most break of the tail rotor driveshaft displayed torsional fracture signatures.
All engine mounts remained secure except the right front, which separated from the airframe. The engine N1 and N2 systems turned freely and were continuous to the starter and main rotor, respectively. Damage to the first stage compressor blades was noted consistent with foreign object ingestion. Fuel was noted in the line to the fuel nozzle, and the nozzle was absent of obstruction. The upper and lower magnetic chip detectors were absent of contamination.
A 27-foot length of the red-colored, external-load sling remained attached to the helicopter's cargo hook. The remaining 13 feet of sling, with grappling hook attached, was located at the base of the tower. The equipment used by the linemen for their work on the tower remained attached to the grappling hook via straps. One of the three prongs of the grappling hook was bent slightly inward, towards the center shaft of the hook. Testing of the helicopter's external cargo hook revealed that both the electrical and manual release systems functioned normally.
Examination of the transmission tower revealed several red-colored fiber transfer marks along the top span of the transmission tower. Several abrasions and gouges of the tower's structure were noted about 16 feet below the fiber transfer marks. Linemen performing a post-accident inspection of the tower, under the direction of a Safety Board Investigator, suspended the separated lower portion of the sling and grappling hook from the tower at the point where the fiber transfer marks were observed, which placed the grappling hook directly adjacent to the abrasions on the tower structure.
TESTS AND RESEARCH
A hand-held global positioning system (GPS) receiver was recovered from the wreckage and forwarded to the Safety Board's Vehicle Recorders Laboratory for data extraction. Download of the data showed that accident flight was approximately 2 hours and 53 minutes in duration. The first data point was recorded at 0737:09. For approximately the first 19 minutes of flight from 0737 to 0756, the helicopter headed in a southeasterly direction. At 0756:00, the helicopter was approximately 30 miles from the start of the flight and for the remaining data (from 0756:00 to 1030:20), the helicopter moved from west to east and then back again several times while covering a 3-mile area.
Near the end of the data from 1025:12 to 1030:10, the helicopter remained within a 0.2 mile area while the GPS altitude stayed between 2,700 feet to 2,800 feet and the ground speed remained under 3 mph and went as low as 0.1 mph. At 1030:10, the helicopter was at a GPS altitude of 2,708 feet with a ground speed of 0.1 mph and five seconds later at 1030:15, the ground speed increased to 5 mph while the GPS altitude slightly decreased to 2,702 feet. Five seconds later, at the last data point, the ground speed increased to 6 mph and the GPS altitude decreased to 2,601 feet.
The operator developed Task Analysis documents that specified the responsibilities of the pilot and other persons involved in the operator's unique work. Task Analysis 002, "Approach to, Transfer Lineman on/off and Departures from a Structure", procedure "H. Departure from the structure" defined the potential operational risks during this phase of the task as; obstacle clearance, helicopter performance with additional weight, helicopter restrained by bond or safety connections, or helicopter malfunction. The recommended risk reduction procedure for this phase of task stated: "The pilot shall be cognizant of emergency procedures and plans at all times. The lineman shall insure all objects, (bonding, personal safety gear and etc) are clear between the helicopter and the structure. The lineman shall communicate, 'Clear to leave' when appropriate. The pilot will assure: right-of-way clearance, structure clearance, wind direction and velocity, gross weight, power available, and lineman and equipment are stowed and secured. The pilot shall respond, 'Leaving structure' when appropriate. The departure shall be performed in a slow and deliberate manner. The pilot and lineman shall verify that the helicopter is clear to continue departure." The emergency procedure for this phase of the task advised the pilot to performed helicopter emergency procedures in accordance with the rotorcraft flight manual, and specifically advised, "Inadvertent attachment to the structure may be rectified by slowly moving the helicopter back to the work location."
The operators Task Analysis 009, "Helicopter External Load", similarly defined the procedures when working with loads attached to the helicopter's exterior. Under task procedure "D. Load pick-up," the recommended risk reduction procedure stated that after attaching a load to the external sling, the pilot should, "…proceed smoothly without exceeding helicopter power and weight limits and without movement over the ground. The ground crew should notify the pilot of any unusual circumstances noted…" In addition to performing emergency procedures in accordance with the rotorcraft flight manual, the task analysis advised under the emergency procedures section to, "Perform Emergency Load Release in Accordance with Rotorcraft Flight Manual."
The operator's Rotorcraft External Load Flight Manual outlined the operating limitations, normal operating procedures, emergency conditions, and other information deemed essential to safe external load operation. The Emergency Conditions section of the manual advised pilots, "If any difficulties arise during the flight and an emergency landing is necessary, release the [external] load immediately."