Summary
On June 16, 2010, at approximately 1440 mountain daylight time, a Kaman K-1200 helicopter, registration N134WC, impacted terrain about five miles west of Donnelly, Idaho. The commercial pilot, the sole occupant, was killed, and the helicopter sustained substantial damage. The flight was a 14 Code of Federal Regulations Part 133 long-line logging operation that had been airborne for about one hour and 40 minutes. Visual meteorological conditions prevailed, and no flight plan was filed.
History of Flight
According to four witnesses near the site, the helicopter, using a 200-foot long-line, had just lifted a large log off the ground when the accident sequence began. Two witnesses were looking directly at the helicopter; the other two looked after hearing a loud noise. The pilot had attempted to lift the log once before but set it back down due to interference from other logs. He then asked the hooker to reset the choker nearer to the butt end, which caused the log to hang more straight. The pilot transmitted, "That is more like it," and then began lifting again. Just after the log cleared the ground, the two direct witnesses saw an outboard section of a rotor blade separate and fly through the air, followed by a loud bang. The other witnesses heard the noise and saw blade pieces flying. Other portions of the blades and structure then separated. The helicopter went out of control, descended inverted, and came to rest. There was no fire.
Witnesses reported no unusual engine or rotor sounds before the accident. Two experienced helicopter workers stated they would have recognized abnormal sounds. One witness stated the lift appeared normal and the pilot did not ascend faster than usual or jerk the log. Witnesses confirmed no contact with trees or obstacles.
Aircraft and Pilot Information
The pilot, a 64-year-old male, held a Commercial pilot certificate with a helicopter rating and an airplane single-engine land rating. His last FAA second-class medical was issued on March 18, 2001, without limitations. His total pilot time was estimated at 27,600 hours, with 12,600 hours in the Kaman 1200. His last flight review was on December 8, 2008, in a Robinson R-22.
The aircraft was a 1996 Kaman Aerospace K-1200 KMAX helicopter, serial number A94-0006, registered as N134WC. It was powered by a Honeywell/Lycoming T53-17A1 engine rated at 1,500 horsepower. The last progressive inspection under its Approved Airworthiness Inspection Program was on June 15, 2010. At the time of the accident, the airframe had accumulated 24,053 hours.
Meteorological Information
The helicopter was operating under a 12,000-foot overcast ceiling. Winds were calm to variable at six knots. Visibility was more than ten miles. Temperature was about 45 degrees Fahrenheit.
Wreckage and Impact Information
The lift occurred at approximately 6,300 feet elevation on the southeast-facing down-slope of North Business Mountain. The wreckage came to rest inverted over the log, about 410 feet southeast of the lift location, at approximately 6,180 feet elevation. The wreckage included the main fuselage, cockpit, landing gear, engine, transmission, right rotor mast pylon, stabilizers, and tail boom. Both horizontal stabilizers were rotated 180 degrees. The tail boom had twisted and torn. The belly hook was open, and the long-line was wrapped around the fuselage and left stabilizer. The remote hook was connected to the choker, still attached to the log about three feet from its butt end. No marks on the long-line indicated contact with rotor blades.
The transmission had sheared the KAFlex coupling. Rotor hub fractures released blades 94A and 94B. The left pylon separated from the transmission. Examination of all four blades revealed fractures consistent with overstress. Blade 94B and 169B showed witness marks indicating leading-edge contact. The servo flaps exhibited damage consistent with impact.
Tests and Examinations
The wreckage was recovered to SP Aircraft in Boise, Idaho, where layout inspection was conducted. Blades 94B and 169B were sent to Kaman Aerospace for X-ray inspection and then to the NTSB Materials Laboratory. The inspections revealed:
- All fractures were overstress; no preexisting fatigue cracks.
- Left and right transmission chip detectors were clean.
- All flight control components moved freely except where impact-damaged.
- Blade-to-blade contact evidence: blade 94A showed scrape marks consistent with left main rotor hardware; blade 94B leading edge damage matched blade 169B.
- X-ray found no preexisting blade spar cracks or delaminations.
- Engine examination showed rotational and thermal damage consistent with power production. Extensive foreign object damage from airframe fittings. Power turbine and gearbox rotated freely. A peak engine NG of 101.4% was recovered from the NG RPM indicator, but not positively linked to the accident. Exceedance flags were recorded on load and torque indicators, but no ball codes.
Additional Data
The operator weighed the long-line (146 pounds), choker (15 pounds), and log (6,330 pounds), totaling an external load of 6,491 pounds. The helicopter's maximum permissible external load was 6,000 pounds. The operator calculated the helicopter weight at 5,797 pounds.
An autopsy determined the cause of death as blunt force trauma and the manner as accidental. Forensic toxicology by CAMI was negative for carbon monoxide, cyanide, ethanol, and listed drugs.