Beluga, AK, USA
C-GYPH
EUROCOPTER AS350 B3
The commercial helicopter pilot was transporting a 1,000-pound external sling load attached to a lightweight, synthetic 100-foot long-line when the load began to spin and swing underneath the helicopter. As the helicopter neared its destination, it suddenly yawed, and then started to spin uncontrollably, and the pilot immediately jettisoned the external load. As the helicopter continued to spin uncontrollably, it descended into an area of tall trees and then came to rest on its left side. A postaccident inspection of the helicopter revealed that portions of the severed lightweight synthetic long-line had become entangled in the tail rotor gearbox output shaft and that the tail rotor gearbox assembly was torn free of the tail boom. Examination of the long-line revealed that its entire length was tightly wrapped, knotted, and kinked. The pilot reported that he had not received training in procedures to adequately stabilize external sling loads. Given the postaccident condition of the lightweight synthetic long-line, the pilot's statements, and the lack of a rotating swivel, it is likely that, once the external load began to spin, the long-line continued to tangle and tightly knot and ultimately reached its breaking point. Once the synthetic long-line separated, the portion still attached to the belly of the helicopter recoiled upward and eventually became entangled with the tail rotor gearbox output shaft. In addition, it is likely the pilot did not adequately monitor the condition of the external sling load while en route, and he failed to recognize the need to stabilize the load.
HISTORY OF FLIGHTOn December 15, 2012, about 1005 Alaska standard time, a Eurocopter AS350-B3 helicopter, Canadian registration C-GYPH, crashed in an area of tall trees near Beluga, Alaska. The helicopter was being operated as a 14 CFR Part 133 external load flight, by Prism Helicopters, Inc., Wasilla, Alaska, in support of a geophysical survey project. Visual meteorological conditions prevailed at the time of the accident, and company flight following procedures were in effect. The pilot, the sole occupant, received serious injuries. The flight originated at a remote survey site about 13 miles north of Beluga, and it was en route to Beluga at the time of the accident. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on December 15, the operator's president and director of safety said the accident helicopter was en route to the Beluga Airstrip with a composting toilet that weighed about 1,000 pounds attached to a lightweight, synthetic, 100-foot long-line underneath the helicopter. A ground crewmember who was waiting for the helicopter to arrive in Beluga heard the pilot announce over their company radio frequency, in part: "I'm going down." No further radio communications were received. A search for the missing helicopter was launched. About 30 minutes after the accident, the Alaska State Troopers received a 911 distress call from the badly injured pilot on his cell phone stating that he had crashed. He was unable to give his location. Concurrently, the operator, from their Wasilla headquarters, reviewed the archived Sky Connect satellite tracking data, which provides management personnel with real-time position reports about every minute, and subsequently relayed the missing helicopter's last known position to searchers near Beluga. Shortly thereafter, the accident helicopter was found by another helicopter that had been working in the area. The wreckage was found in an area of tall trees, and snow-covered terrain. In a written statement to the NTSB received January 25, the pilot wrote that before the accident he was flying a company owned Eurocopter AS350 B2 helicopter. The day of the accident was the first day he flew the AS350 B3 helicopter on that project, but he elected to use the same long-line that he had been using with the AS350 B2 helicopter. He said that he preferred using the previous long-line since it had a weighted hook that had been painted an orange/red color, which made it much easier to see against the snow covered terrain. The lightweight synthetic 100-foot long-line he elected to use did not have a rotating swivel. He said that when he arrived at the remote site, he elected to remain in the helicopter, with the engine operating. After the ground crew members attached the 100-foot long-line to the belly hook on the helicopter, and the other end to a 4-point cable harness on top of the composting toilet, he momentarily hovered the helicopter, then ascended vertically over the load to ensure that the long-line was not knotted or kinked. He lifted the load up and away laterally from the site, and climbed toward 1,000-1,500 feet above sea level. The pilot said that at 70 knots the load started flying erratically, spinning, and swinging back and forth (left to right) more than he liked. He slowed the helicopter, and found that the load flew well at 60-65 knots. He noted that it had a "nice gentle slow spin to it, and it swung left to right very little." He continued the 14 mile trip at 60-65 knots. About 2 miles from the Beluga Airstrip, with his altimeter reading 1,000 feet, he felt a "tug," which prompted him to evaluate the condition of the load. The load was flying differently, and he thought a strap might have broken. Unable to see the load below the helicopter, he then felt the helicopter yaw, then start to spin, and he immediately jettisoned the load using the mechanical release mechanism. The helicopter continued to spin uncontrollably, and he assumed that there had been a loss of tail rotor control, so he reduced the throttle in an attempt to gain control. The helicopter subsequently descended into an area of tall trees, coming to rest on its left side. PERSONNEL INFORMATIONThe pilot age 29, held a commercial pilot certificate with ratings for helicopter. He was issued a second class airman medical certificate without limitations on March 8, 2012. According to flight records, the pilot had about 3,037 hours of total flying experience, 48 of which were in the same make and model as the accident helicopter. He had accrued 32 of those hours in the same model helicopter in the preceding 90 days. AIRCRAFT INFORMATIONThe helicopter was a Eurocopter AS350 B3, manufactured in 1982, and equipped with an Arriel 2B turbo shaft engine. The helicopter had accrued about 5,558 hours of operation at the time of the accident, and was maintained under a manufacturer's inspection program. A 100-hour inspection of the helicopter was completed on August 13, 2012. An examination of the helicopter and engine log books by the NTSB IIC showed no mechanical issues with the helicopter prior to the accident. The helicopter was equipped with a Sky Connect satellite tracking system. A review of the tracking data did not show any unusual tracks, turns, or speed variations, until the loss of control prior to the accident. METEOROLOGICAL INFORMATIONThe closest weather reporting facility was the Anchorage International Airport, 32 miles east of the accident site. At 0953, an Aviation Routine Weather Report (METAR) was reporting, in part: Wind, 340 degrees (true) at 3 knots; visibility, greater than 10 statute miles; clouds and sky condition, 7,000 feet few; temperature, 7 degrees F; dew point, 3 degrees F; altimeter, 29.15 inches Hg. VFR weather conditions existed at the time of the accident. AIRPORT INFORMATIONThe helicopter was a Eurocopter AS350 B3, manufactured in 1982, and equipped with an Arriel 2B turbo shaft engine. The helicopter had accrued about 5,558 hours of operation at the time of the accident, and was maintained under a manufacturer's inspection program. A 100-hour inspection of the helicopter was completed on August 13, 2012. An examination of the helicopter and engine log books by the NTSB IIC showed no mechanical issues with the helicopter prior to the accident. The helicopter was equipped with a Sky Connect satellite tracking system. A review of the tracking data did not show any unusual tracks, turns, or speed variations, until the loss of control prior to the accident. WRECKAGE AND IMPACT INFORMATIONThe helicopter was not examined at the remote crash site. Photographs provided by the operator, showed that the helicopter had descended through a heavily treed area, and came to rest on its left side. The fuselage, tail boom, and rotor system sustained substantial damage. The operator located the sling and load the helicopter had been carrying, near the accident site. The load was a metal, self-composting toilet, weighing about 1,000 pounds, which was equipped with a 4-point cable harness on top. The 4-point cable harness was attached to a D-ring which in turn was attached to the non-swiveling hook. The 100-foot long synthetic long-line was equipped with an electrically actuated hook at one end, and a large D-ring at the other end. The synthetic long-line was then attached to the non-swiveling belly hook on the helicopter. Additional photographs showed the four independent harness cable twisted together, and the synthetic lifting line was twisted and knotted at the load end of the line. The synthetic long-line was separated and had frayed ends at the point of separation. The lifting gear was examined and photographed by the NTSB IIC at the operator's Wasilla, Alaska facility. Measurements of the synthetic long-line showed that it had separated about midway between the helicopter and the load. Photographs also showed the section of the synthetic long-line above the separation, which had been attached to the helicopter's belly hook, was about 40 feet long, and it was wrapped tightly around the tail rotor gearbox output shaft. The tail rotor gearbox had twisted free from its mounts on the tail boom, and departed the helicopter in-flight. ADDITIONAL INFORMATIONThe long-line is a synthetic woven/braided multiple strand line, about 100 feet in length. The line has loops on either end. The long-line itself does not have attachments or hardware. Suitable attachments and hardware can be added to either end depending on the mission. External Load Pilot Training Each FAA approved helicopter operator is tasked with developing pilot training appropriate to their organization, with guidance from the FAA. Prism Helicopters had a training program approved by the FAA, which allowed the pilot to attain CFR Part 133 certification. According to the pilot, his long line experience consisted of about 290 hours, most of which was with Prism Helicopters, and in several different helicopter makes/models. The pilot said during his training, he was never told how to use a drag/drogue chute to stop a load from spinning, and said the operator did not have chutes available. 14 CFR Part 133 and Federal Aviation Administration (FAA) Advisory Circular (AC) 133-1A provide information for rotorcraft external-load operations, and are the basis for the operator's development of a suitable training program. CFR Part 133 includes two areas, knowledge and skills. The knowledge requirement, Step 2 includes; Proper methods of loading, rigging, or attaching the external load. The skill requirement does not address load rigging. AC 133-1A, Titled; Rotorcraft External-load operations in Accordance with FAA Part 133. The AC generically addresses flight and load planning, helicopter performance, airspace considerations, and certification. The AC does not address rigging. FM 4-20.198, Military Field Manual Multiservice Helicopter Sling Load: Single-Point Load Rigging Procedures The military has developed a system for rigging/certifying recurring loads. This allows similar loads to be rigged and transported in a proven safe manner. Unusual and one-time loads must be rigged by a person qualified/trained to stabilize loads for transport. There are commercially available programs from training providers. COMMUNICATIONSThe helicopter was operating at a remote site, and communicating on a company frequency. The last transmission heard by a company ground-crewman was the pilot saying that the helicopter was going to crash.
The pilot's failure to stabilize the external load, which led to the synthetic long-line separating about midspan and the remaining line becoming entangled in the tail rotor gearbox output shaft and resulted in the separation of the tail rotor gearbox and subsequent loss of control. Contributing to the accident was the pilot's inadequate training.
Source: NTSB Aviation Accident Database
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