Chickaloon, AK, USA
N213EH
EUROCOPTER AS 350 B2
**This report was modified on July 7, 2015. Please see the public docket for this accident to view the original report.** The commercial pilot was on a Part 135 passenger flight transporting telecommunication technicians to remote sites. A technician was left at one site, and when the helicopter did not return, he contacted his employer. His employer contacted the helicopter operator. Unable to make contact with the helicopter, the operator contacted the FAA, and reported the helicopter overdue. A search for the helicopter was initiated based on a position report from the helicopter's onboard commercial satellite tracking system. A snowstorm in the search area precluded the use of aircraft in the search, and ground searchers were unsuccessful. A State Trooper helicopter found the crash site the next morning when the weather improved. The pilot and three passengers were found dead; the fourth passenger, the minor stepson of one of the technicians, had head injuries and hypothermia. According to the operator and survivor, after transporting the first technician, the helicopter landed at a rest area near the highway and picked up another technician and his stepson prior to going to the next site. The stepson was in the left front seat, and the three technicians were in the rear seats. The destination site was about 2.5 miles from the rest area across a ravine. A motorist on the highway saw the helicopter depart from the rest area, and then make a steep descent into a ravine. He said he thought the descent was unusual, but he did not see any impact, and thought the helicopter was working in the ravine. He said the visibility was about 2 miles, and it was snowing lightly. The helicopter impacted terrain approximately in a level attitude in a near vertical descent, about three-quarters of a mile from the rest area. The terrain at the accident site was rough and uneven, covered with trees, high brush, and snow. The accident flight lasted less than 2 minutes. The surviving front seat passenger recalled the liftoff and departure, then said he felt like he was falling, and that the pilot told everyone to "hold on we're going to crash." The main rotor blades remained attached to the rotor head; two of the blades were resting on the ground, and the third blade was suspended over the ravine. The uncut brush surrounding the two blades resting on the ground and the downward chordwise bend of the suspended blade were consistent with low rotor rpm at final impact. Examination of the helicopter's engine and drive train revealed damage signatures indicative of an overtorque event. These signatures included a 7 millimeter misalignment of the engine's module 5 drive nut and torsional damage (twisting) of the engine-to-transmission driveshaft, which shortened the driveshaft, allowing the splines at the aft end of the shaft to disengage, disconnecting the engine from the main transmission. The module 5 drive nut misalignment was consistent with the engine free turbine producing power at the time of the drive nut overtorque. The direction of rotational smearing damage observed on a portion of the splines was indicative of the engine continuing to provide power for a short time after the driveshaft twisted and shortened. The directionality of the driveshaft twisting was consistent with an opposing torque load forward (on the transmission side) of the driveshaft, which could have resulted from a main transmission seizure or a main rotor impact event. Disassembly and examination of the main transmission revealed no evidence of a seizure. Therefore, the overtorque likely resulted from one or more main rotor blade strikes occurring while the engine was powering the main rotor system. Further, the overtorque damage likely occurred before the helicopter's final impact in the ravine because the low rotor rpm signatures observed at the accident site indicated that the engine was not powering the main rotor system and that the rotational energy in the system had been significantly dissipated before that impact. The helicopter's main rotor blades did not exhibit the extensive damage typically seen when powered blades impact terrain (such as fragmentation, twisting, and severe leading-edge damage). However, the outboard sections of the blades did exhibit leading-edge dents and chordwise scratches. Thus, the blades likely impacted relatively soft objects, such as a snow bank or brush, which resulted in the overtorque signatures found on the module 5 drive nut and the engine-to-transmission driveshaft without significant destructive damage to the blades. About 2 months after the accident, investigators searched along the route of flight and found no evidence of a main rotor blade strike (such as ground scars or damaged vegetation); any evidence of impact likely had been obscured by that time. The engine also showed evidence of an overspeed. Following the overtorque, the sudden disconnection of the main transmission from the engine unloaded the engine and allowed the free turbine to overspeed to more than 150% free turbine rpm, resulting in free turbine blade shedding and loss of engine power. When the main transmission disconnected from the engine, the main rotor rpm immediately began to decay, leaving the pilot no option other than to initiate an autorotation. The low rotor rpm signatures observed at the accident site indicated that the pilot likely autorotated but could not sufficiently arrest the helicopter's vertical descent rate, resulting in a hard impact with terrain. Given the rough and uneven terrain and the helicopter's low altitude, a successful autorotation landing was improbable. Also, the operator's failure to closely monitor the flight's progress and to make timely inquiries into its whereabouts delayed the search and rescue of the survivor and likely added to the severity of his injuries (hypothermia). The floor-mounted fuel flow control lever (FFCL) was found captured by fuselage crush in the forward emergency range, and the emergency fuel shutoff lever was captured in the aft shutoff position. During impact, the removable acrylic left chin-bubble popped out, and was found about 3 feet in front of the helicopter's nose. A backpack belonging to the surviving passenger was found between the chin bubble and the nose of the helicopter. All other baggage/cargo was found stowed aft and secured. According to the manufacturer, inadvertent movement of the floor-mounted FFCL into the forward emergency range can cause the engine to overspeed within seconds in certain conditions. Because the FFCL is on the helicopter's cabin floor, situated near the front seat passenger's right foot, and is easily moved with minimal pressure, a scenario involving the passenger's foot or his backpack inadvertently moving the FFCL into the emergency range during the flight and causing the engine to overspeed was considered. However, there was no heat damage to the engine's compressor turbine wheels as would be expected due to the excessive influx of fuel into the engine that would immediately result from movement of the FFCL into the emergency range during flight. Further, this scenario does not account for the overtorque damage to the engine's module 5 nut and the engine-to-transmission driveshaft, which had to occur when the engine was producing power (before shedding of the free turbine blades). Therefore, it is not likely that inadvertent movement of the FFCL caused the engine overspeed. Although the reason for the FFCL being in the emergency range could not be determined, it is possible that because it can be easily moved, it was displaced into the emergency range during the impact sequence.
**This report was modified on July 7, 2015. Please see the public docket for this accident to view the original report.** HISTORY OF FLIGHT On April 15, 2008, about 0923 Alaska daylight time, a Eurocopter AS-350-B2 helicopter, N213EH, sustained substantial damage during an emergency descent and impact with terrain, about 34 miles east of Chickaloon, Alaska. The helicopter was being operated as a visual flight rules (VFR) cross-country passenger flight under Title 14, CFR Part 135, when the accident occurred. The helicopter was owned and operated by ERA Helicopters, LLC., Anchorage, Alaska. The commercial pilot and three passengers were killed, and one passenger, the 15-year-old stepson of one of the deceased passengers, sustained serious injuries. Visual meteorological conditions were reported in the area at the time of the accident, and company flight following procedures were in effect. The flight originated at the operator's base in Anchorage about 0742, en route to various communication sites near Chickaloon. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on April 17, the operator's general manager reported that the purpose of the flight was to shuttle State of Alaska telecommunications technicians and equipment between three remote communication sites near Chickaloon. He noted the helicopter departed the Anchorage base with only the pilot aboard. The manager said that the pilot was instructed to land at the State of Alaska's telecommunication heliport in Anchorage to pick up three technicians and their equipment, and then fly to the communication sites near Chickaloon. During a telephone conversation with the NTSB IIC on April 17, a technician that was aboard the helicopter when it departed from the Anchorage telecommunications facility reported that after departure the crew planned to meet an additional technician at the first of three communication sites to drop off equipment. He said as they approached the first site they realized that the technician they planned to meet was not there, so they continued to the second site. The technician said the helicopter landed at the second site about 0900, and left him there. It was agreed that the helicopter would return by 1300 to pick him up. The technician reported that after the helicopter departed from the second site, and before continuing on to the third site to drop off the two remaining technicians and their equipment, the pilot was to fly to a rest area along the highway, and pick up one other technician that would be waiting with additional equipment to be transported to the third communication site. The technician said he was unaware that the other technician would have his stepson with him. When the flight failed to return by 1300, the technician contacted the State of Alaska's telecommunications shop, but was told that the other technicians had a lot of work to do, and to give them more time. When the flight still had not returned by 1400, the technician again contacted the State of Alaska's telecommunications shop. As a result, the State notified the operator, who attempted unsuccessfully to contact the helicopter via satellite telephone and aircraft radio. The operator reported the helicopter overdue to the Federal Aviation Administration (FAA) at 1540, and they contacted the Air Force Rescue Coordination Center. The Air Force Rescue Coordination Center (AFRCC) at Elmendorf Air Force Base, Anchorage, had received the first alert of a signal from a 121.5 MHZ emergency locator transmitter (ELT) signal at 1121 that day. They were unaware at the time that the accident helicopter had crashed, but were already in the process of organizing a search related to the unknown source of the ELT signal. Personnel of the Alaska State Troopers, Civil Air Patrol, Alaska Mountain Search and Rescue, and the Alaska Air National Guard, were dispatched to search for the helicopter, but blizzard weather conditions limited search personnel to a ground search until weather conditions improved the next day. The helicopter's wreckage was located on April 16, about 0750, in an area of hilly, tree-covered terrain, about three-quarters of a mile from the highway rest area where the technician and his stepson were picked up. Additional details of the search and rescue follow in the Search and Rescue section of this report. During an interview with the NTSB IIC on May 27, the sole survivor of the accident, a 15-year-old juvenile, reported that he was asked to accompany his stepfather, who was a telecommunications technician with the State of Alaska, to the third communication site. The boy said that after the helicopter landed in the parking area of the highway rest stop, the pilot shutdown the helicopter before additional equipment was loaded. He said that before departing from the parking lot, he was placed in the front left seat, and the other three passengers were seated in the aft seats. The juvenile noted that he took with him a small day-pack, which contained a bag lunch and two bottles of water. He did not recall where he placed the day-pack. Due to injuries sustained in the accident, the juvenile said he was unable to recall many details of the accident. According to management personnel with ERA Helicopters, and management personnel with the State of Alaska's Telecommunications Division, neither knew that the juvenile was on board the accident helicopter. On the morning of the accident, a motorist about one mile south, traveling northbound on the highway saw the helicopter lift off from the roadside, and fly in an east south-east direction. The motorist estimated the visibility to be about 2 miles in light snow. He said he saw the helicopter flying below the overcast, and it made a steep descending right turn toward the ground. He said initially he thought the helicopter was going to crash, but as he approached the area where the helicopter departed, he saw the ravine where the helicopter made the descent. The motorist was familiar with helicopter operations from his job working on the Alaska pipeline, and thought the helicopter was probably working in the ravine. He said it was not unusual to see helicopters working along the highway, but he thought the steep descent was unusual, and commented to a friend after arriving at his work site, about the helicopter and the scary ride the pilot must have given the passengers. He said he did not hear about the accident until several days later, and then contacted the IIC. INJURY TO PERSONS The pilot and four passengers were aboard the helicopter at the time of the accident. The helicopter wreckage was reached by rescuers about 24 hours after the accident. The pilot in the right front seat and the two passengers in the right rear and center rear seats were found dead in the helicopter. The third passenger in the left rear seat had exited the helicopter, and was found dead outside the helicopter. The fourth passenger, the juvenile, had been seated in the left front seat, and was found incoherent, wandering in a ravine at the base of the slope where the helicopter impacted. He was transported to a hospital in an Alaska State Trooper helicopter, and according to the transporting helicopter's observer/EMT, he had a head injury, and was suffering from hypothermia. DAMAGE TO AIRCRAFT The helicopter received substantial damage to the fuselage, tail boom, tail and main rotor systems, and the rotor drive train. PERSONNEL INFORMATION The pilot held a commercial helicopter certificate with a helicopter instrument rating. He also held a helicopter flight instructor certificate with an instrument helicopter rating. His most recent second-class medical certificate was issued on March 5, 2008, and contained no limitations. According to the Pilot/Operator Aircraft Accident Report, (NTSB Form 6120.1) submitted by ERA Helicopters, the pilot's total aeronautical experience was about 3,747 flight hours, of which about 1,889 flight hours were in the accident helicopter make and model. In the preceding 90 and 30 days prior to the accident, the pilot flew a total of 47.3 and 9.6 flight hours. The operator's pilot training records showed no deficiencies, and that the accident pilot had completed all required training, including a required CFR Part 135 proficiency check ride on June 11, 2007. AIRCRAFT INFORMATION The helicopter was a Eurocopter AS-350-B2, equipped with a Turbomeca Arriel 1D1 turboshaft engine. The helicopter was maintained under the operator's Approved Aircraft Inspection Program (AAIP), which requires inspections to be performed approximately every 100 flight hours. The helicopter had 4,983.7 flight hours in service at the time of the accident 11 flight hours had elapsed since the most recent phase inspection. An examination of the helicopter's maintenance logs showed no mechanical discrepancies. METEOROLOGICAL INFORMATION The technician who was dropped off at the second communications site said the weather had been good along the route from their departure in Anchorage to the site where he left the helicopter, but by 1400 he said he could see bad weather rapidly approaching from the southwest. He said he knew that if they did not depart soon the approaching weather would preclude the use of the helicopter. The helicopter did not return, and the technician spent the night at the communication site due to the snowstorm that arrived shortly after 1400. The closest weather reporting station was the automated weather station at Sheep Mountain Airport, 4.5 miles to the west of the accident site. The automated weather observation at 0850 ADT the morning of the accident recorded the wind from 250 degrees at 3 knots, visibility 2 statute miles, ceiling 400 feet overcast, altimeter 29.42 inches of mercury, temperature 27 degrees F, and dew point 23 degrees F. The accident site was about three-quarters of a mile to the east of the Glenn Highway (Alaska Highway 1). The highway follows a river valley bounded on both sides by rising terrain. There is an FAA weather camera co-located with the State of Alaska communication tower at Tahneta Pass, the helicopter's destination, about 1.5 miles southeast of the accident site. There is an FAA automated weather station and camera at Sheep Mountain, about 5 miles north-northwest of the accident site. Weather station and camera data from both locations showed VFR conditions at the lower part of the helicopter's route, and marginal VFR conditions in the area of the accident. Visibility varied from 1-2 miles in light snow, and ceilings varied from 300-500 feet above the terrain with patches of blue sky visible. A detailed meteorological evaluation prepared by an NTSB meteorologist is in this report's public docket. COMMUNICATIONS There were no known communications with the helicopter after its departure from the State of Alaska's communication facility in Anchorage. The helicopter pilot had a satellite telephone available in the helicopter, and according to the operator, he routinely called in upon reaching his destination. The morning of the accident the pilot did not report arriving at the destination, but such routine reporting is not required by the operator's policy, and no action was taken. The helicopter was equipped with a commercial satellite tracking system provided by Sky Connect, Takoma Park, Maryland, which allowed monitoring of the helicopter's movements by the operator. The position of the helicopter was displayed on a map representation on computer terminals at the operator's Anchorage facility, and according to the operator, information was updated in about one minute intervals. The geographic display was a small scale, large area map presentation with very little detail. A list of the helicopter's Global Positioning System (GPS) coordinates, airspeed, altitude, heading, and time were viewable on additional computer pages available at the operator's Lake Charles, Louisiana, facility, but not available at the Anchorage facility. The track data provided by the operator shows each leg of the day's flights starting with "power on", then "departure" (signaled by collective movement and/or airspeed indication), followed by "scheduled" (data transmissions from the helicopter), then "arrival" (signaled by collective down), and finishes with a "flight summary." The last entry for the accident helicopter, in the history information data provided from the Lake Charles facility showed, 04/15/08, 09:30.41, "OVERDUE," meaning that the helicopter's equipment stopped transmitting data prior to the arrival sequence. The "OVERDUE" information was not available to the operator in Anchorage. According to the satellite data, the accident flight from departure at the roadside to the accident site lasted less than one minute. The operator's personnel at Lake Charles did not monitor Alaska flights, and no known "overdue" alarm was set. According to the operator in Anchorage, the position of the helicopter had been noted, but on the large area display the helicopter appeared to be near one of several destinations scheduled for that day. The operator made no attempt to contact the helicopter throughout the day, until the State reported to the operator that the helicopter had not returned to pickup the technician at the second communication site. WRECKAGE AND IMPACT INFORMATION On April 16, 2008, the NTSB IIC, along with an Alaska State Trooper, and an FAA airworthiness inspector from the Anchorage Flight Standards District Office (FSDO), traveled to the accident site via helicopter and examined the wreckage. The third communication site, the helicopter's destination (elevation 3,681 feet), was 2.2 miles and across a ravine from the pickup/departure point (elevation 3,259 feet), a rest area along Alaska State Highway 1. On a clear day the destination communication site is visible from the highway. The accident site is about three-quarters of a mile from the departure point in the general direction of the destination, but south of a direct line to the destination. All of the helicopter's major components were found at the main wreckage site. The helicopter impacted on the steep west side embankment of a dry ravine, which leads generally southeast to a river. The helicopter was about 30 feet from the top of the ravine, and about 80 feet from the bottom. The embankment incline was approximately 35-50 degrees, and was covered with willow brush, and about 3-5 feet of snow. Several inches of snow had fallen on the helicopter since the accident. The helicopter came to rest on the embankment facing approximately southeast, parallel to the embankment. The impact crater and crush lines were consistent with a steep vertical descent. The fuselage was in a level attitude, and the right side pilot's door was displaced aft about 4 feet. The transmission was leaning to the right (into the bank), and all three main rotor blades had impact damage. On the AS-350-B2 helicopter the main rotor blades and their associated components are color coded red, blue, and yellow. The red main rotor blade was pointed forward in relation to the fuselage, and had leading edge damage. Its trailing edge was split open in numerous areas, and about 18 inches of the lower skin was torn near the tip. The tip was touching the ground in front of the helicopter, and the red blade had standing willow bushes on both sides. The blade remained attached to the Starflex rotor assembly. The blue blade was pointed to the right of the fuselage and flexed upward into the ascending bank. The blade was punctured and torn vertically about mid-span, and came to rest in a willow bush, with unbroken branches on both sides of the blade. The blade remained attached to the Starflex rotor assembly, and the blue star arm was broken near the outboard frequency adapter. The yellow blade was pointed to the left, and suspended over the ravine. The blade had leading edge damage, and a sharp downward bend about 3 feet from the grip. From the bend outward the trailing edge of the blade was splayed open. The blade remained attached to the Starflex rotor assembly; however the yellow star arm was fractured about mid-span with an angular fracture s
An in-flight overtorque of the engine-to-transmission driveshaft resulting in disconnection of the main transmission from the engine. The overtorque likely occurred due to an in-flight main rotor blade contact with snow-covered terrain, precluding significant main rotor blade damage and ground scarring. Contributing to the severity of the surviving occupant's injuries was the helicopter operator's failure to properly monitor their satellite flight-following system and to immediately institute a search once the system reported that the helicopter was overdue.
Source: NTSB Aviation Accident Database
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