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N355EV accident description

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Tail numberN355EV
Accident dateAugust 13, 2006
Aircraft typeEurocopter AS-350-B3
LocationYellow Pine, ID
Near 45.0075 N, -115.711111 W
Additional details: None

NTSB description

HISTORY OF FLIGHT

On August 13, 2006, at approximately 1710 mountain daylight time, a Eurocopter AS-350-B3 helicopter, N355EV, was destroyed by fire following impact with the East Fork Road (US Forest Road 48) about 18 miles west of Yellow Pine, Idaho. The commercial pilot and his three passengers were fatally injured. The helicopter was being operated under contract to the United States Forest Service by Evergreen Helicopters, Inc. of McMinnville, Oregon, as a public use flight. Visual meteorological conditions prevailed for the cross-country flight that had originated approximately 5 minutes before the accident. A company flight plan had been filed. The helicopter was en route from Williams Peak (elevation 6,826 feet) lookout tower to Krassel Helibase (24K; elevation 3,982 feet) when the accident occurred.

At 1656, the flight-tracking log for the helicopter indicated that it departed Krassel Helibase to transport a relief Fire Lookout to Williams Peak lookout tower and return. The relief Fire Lookout reported that the flight (approximately 4 nautical miles [nm] and 2,844 feet elevation gain) was "very normal and smooth." He said that forest fire smoke limited the visibility in the lower valley to approximately 1 mile, but as the helicopter flew up the ridge, visibility got much better. The relief Fire Lookout said that the pilot flew up the mountain by following the terrain with 100 to 200 feet of clearance. He said that there were two forest service personnel on board, to assist in off-loading and on-loading equipment, supplies, and refuse from the external cargo baskets, to minimize the aircraft's time at Williams Peak. He said the helicopter departed between 1705 and 1710, with the Fire Lookout person who was going off duty and the two other employees.

There were no witnesses to the accident. A U.S. Forest Service employee discovered the accident at approximately 1730. The aircraft was consumed by postimpact fire.

PERSONNEL INFORMATION

The pilot's most recent Federal Aviation Administration flight medical exam (second class) was taken on July 1, 2006. The pilot's flight logbook, as of December 2005, and his employer's payroll records indicated that he had 4,386 hours of flight time. The pilot's employer stated that he had completed his last flight review on February 13, 2006. The mission log-sheets, at Krassel Airfield, documented that the pilot had been off duty on August 8 thru 10. On August 11 and 12, he flew 6.6 hours, and on the day of the accident he had flown 3.1 hours. The pilot was in his second year of flying under the Krassel Rappel contract.

During interviews conducted by U.S. Forest Service personnel, four Helitack crew members, who were assigned to the helicopter, said the pilot was very skillful. One crew member described the pilot as "a perfectionist--in everything about his flying--all had to be perfect." They said he did like "showy" flying at times, but would always ask the passengers if they were comfortable. He would "buzz" a ridge every now and then, and perform a maneuver he called the "sleigh ride." One of the Helitack crew members said that a "sleigh ride was where you top a ridge then drop the collective, drop the nose a bit....it was a common maneuver for him."

AIRCRAFT INFORMATION

The helicopter was a single engine, six seat aircraft, which was manufactured by Eurocopter in May 2002. It was powered by a Turbomeca Arriel 2B turboshaft engine, which was rated at 825 horsepower at sea level. Maintenance logbooks indicated that the airframe had 1,384 hours, and the engine had 1,260 hours. The helicopter was equipped with two open-top external cargo baskets whose framework was tubular steel which was covered with expanded steel mesh. They were 52 inches long, 12 inches wide, and 7 inches high, and were secured to the helicopter's skid gear. Cargo was secured inside these baskets by multiple bungee cords.

METEOROLOGICAL INFORMATION

At 1650, the weather conditions at McCall Municipal Airport (elevation 5,021 feet), McCall, Idaho, located 225 degrees magnetic and 18 nautical miles from the accident site, were: wind variable at 5 knots; visibility 10 statue miles; clear of clouds; temperature 73 degrees Fahrenheit; dew point 36 degrees Fahrenheit; altimeter setting 30.10 inches Hg.

At 1710, the sun was at 250.7 degrees magnetic, and 38 degrees above the horizon. Several forest service personnel at Krassel Helibase said that the pilot would commonly navigate by following the mountain ridges. The ridge line from Williams Peak lookout tower to the accident site was a westerly heading (250 degrees) with a left dogleg turn (220 degrees) at the half way point.

WRECKAGE AND IMPACT INFORMATION

The main wreckage was found on Forest Service Road 48 (N45:00:32; W115:42:45; elevation 3,719 feet), also known as East Fork Road. This was in the Payette National Forest, approximately 2,100 feet east of the confluence of the East Fork of the South Fork of the Salmon River and the South Fork of the Salmon River. The surrounding terrain was comprised of steep, rugged mountains, with narrow valleys and sharp ridges. The mountain sides were predominately granite detritus with scattered rocky outcrops. The vegetation consisted of dispersed conifers and native grasses. A ground scar on a 180 degree magnetic orientation terminated at the main wreckage. Additional wreckage was distributed up the mountain side for approximately 2,000 feet (with a 1,230 foot elevation gain) on a north, by north-east heading from the accident site. All of the helicopter's significant components were accounted for.

At the highest point on the mountain, where the initial debris was found (hence, initial-debris-point, or IDP), there was an uprooted, downed snag (a dead, defoliated conifer). An accompanying forester estimated that it had been 90 feet tall. It was broken into several segments, and was oriented approximately 220 degrees magnetic. Several bits/scraps of paper, some with writing/notes on them, were found within 30 feet of the downed snag. Next down the mountain, from approximately 100 to 600 feet below the IDP, were found thirteen cubitainers (5 gallon plastic containers for potable water), and several cubitainer caps and handles. There were two large plastic refuse bags, yellow crepe paper, and a plastic bread sack. The two large plastic bags were torn, and eleven of the cubitainers had 3 to 9 inch slashes in them. One cubitainer had a chip of blue paint in it, which was consistent with the tail rotor paddle paint. Several green and white paint chips, consisting of aircraft primer overlaid with paint, were found in the same general area.

Approximately 550 feet down from the IDP was another large snag with its top broken off in a 220 degree orientation. Down hill from this was a live conifer with a fresh broken limb. West, for approximately 200 feet and down slope for approximately 200 feet, from these two damaged trees, was found a tail rotor paddle which had separated at its cuff. Further down slope, approximately 1,450 feet down from the IDP and aligned with the two damaged trees, was found the tail rotor gearbox cover which exhibited evidence of tail rotor drive shaft flailing. Approximately 80 to 90 feet further down the mountain was the upper WSPS (wire strike protection system) guide, and approximately 60 feet below that was the tail-cone with its vertical and dorsal fins. Approximately 400 feet (200 foot elevation loss) further down the mountain was the main wreckage on the road. On the edge of the road was a tree, approximately 4 inches in diameter, whose top had been severed.

The first piece of debris on the road was an external-load viewing mirror, which had been mounted under the pilot's feet on the right side of the helicopter. Approximately 25 feet further, were the two cargo baskets side-by-side. One basket had burned refuse in it; the second basket was crushed flat with one side bent inward, and was empty of cargo. Approximately 15 feet further was the severely burned fuselage which was followed by the main transmission that had been consumed by postimpact fire. The Starrflex main rotor head lay in its proper orientation to the main transmission; all of its components were present and exhibited fire damage. All three main rotor blades remained attached to their respective blade sleeves. One blade, marked the red blade, had a deformation on the lower surface in its stainless steel leading edge at approximately 8 feet from the center of the mast. This distance was consistent with the distance from the center of the mast to where the WSPS guide was located. All of the blades exhibited impact damage from 20 to 30 inches inboard from their respective tips. All of the main rotor blade tip weights were missing. The three star arms were found fractured at 45 degree angles.

Immediately beyond the main transmission was the engine. It was found upright and aligned approximately 220 degrees magnetic. The turbine blades had separated and were not found at the accident site or in the engine's exhaust duct. Immediately beyond that lay the tail boom, which was inverted and exhibited little fire damage. Both horizontal stabilizers remained attached to the tail boom; the left horizontal stabilizer was minimally damaged, the right horizontal stabilizer was crushed upward, and over onto itself and aft. Approximately 22 feet to the right of the tail boom was the tail rotor gear box with one paddle still attached; the attached paddle was fractured at its cuff. The aircraft manufacturer's representative said that the tail rotor drive shaft to tail rotor gear box coupling and the tail rotor drive shaft were both torsionally separated in a direction consistent with sudden stoppage of the tail rotor.

On September 25, 2006, under the supervision of an NTSB investigator, a postaccident engine examination was accomplished at the manufacturer's facility in Grand Prairie, Texas. Three of the five party members attended: The U.S. Forest Service, American Eurocopter, and Turbomeca, USA. Externally, the engine exhibited wrinkling on its right side in the vicinity of the annular combustion chamber, and the exhaust duct was crushed, wrinkled and bent. The engine manufacturer's representative said that the absence of cracks or rips in the mangled exhaust duct suggested that it was at operating temperature when it was deformed. Additionally, he said there was some "dimpling" of the exhaust duct and at least one exit hole as a result of turbine blades leaving the engine.

The disassembly of the engine, by the engine manufacturer, found the centrifugal compressor and its cover exhibited rubbing, rotational scoring and thermal damage signatures indicative of rotation at the time of impact. The power turbine's containment shield/ring exhibited no deformation or elongation. All of the power turbine blades were sheared from the turbine disc at their designed shear points (at the base of each blade); no separated blades were found in the engine. The power turbine casing exhibited rubbing and thermal signatures. The engine manufacturer said that the loss of the power turbine blades in this manner was indicative of an engine over speed event. This will occur, he said, when the engine's load is suddenly interrupted. The free turbine nozzle guide vane (found just in front of the power turbine) exhibited compression/crushing on its right side and rubbing on its aft side. The single turbine wheel (gas turbine) exhibited no mechanical damage, but did exhibit heat damage and discoloration.

The transmission shaft (engine to transmission drive shaft) was found within the wreckage with both flex couplings still attached. The aircraft manufacturer's representative said that the transmission attachment bolts of the forward flex coupling had separated, and the bolt holes appeared elongated. The engine attachment bolts of the rear flex coupling had also separated. She said that the "rear flex coupling exhibited deformation consistent with the shaft flailing while still attached to the engine output."

During the investigation, no preimpact engine or airframe anomalies, which might have affected the helicopter's performance, were identified.

MEDICAL AND PATHOLOGICAL INFORMATION

The Valley County Coroner, from McCall, Idaho, ordered an autopsy on the pilot. A Forensic Pathologist, associated with the Ada County Coroner's Office, Boise, Idaho, performed the autopsy on August 15, 2006.

The FAA's Civil Aeromedical Institute (CAMI) in Oklahoma City, Oklahoma, performed toxicology tests on the pilot. According to CAMI's report (#200600196001), carbon monoxide and cyanide tests were not performed. The identified volatiles present, were determined to be from other than ingestion; the drug Naproxen, a nonsteroidal anti-inflammatory which is used to reduce pain, inflammation, and stiffness, was detected in muscle samples.

ADDITIONAL INFORMATION

The helicopter, including all components and logbooks, was released to a representative of the owner's insurance company, on February 14, 2007.

(c) 2009-2011 Lee C. Baker. For informational purposes only.