History of Flight
On April 27, 2013, at about 0830 mountain daylight time, a Bell 206B helicopter, registration N150SP, impacted power lines and terrain while maneuvering north of Shepherd, Montana. The helicopter was registered to Tongue Canyon Aviation, LLC, of Worden, Montana, and operated by the pilot under 14 CFR Part 91. The private pilot, the sole occupant, was fatally injured. The helicopter received substantial damage to the fuselage and rotor system. Visual meteorological conditions prevailed, and no flight plan was filed. The local flight originated from the helicopter's home base in Worden at about 0730 to assist with herding cattle on a field north of Shepherd.
A ranch hand witness reported the helicopter maneuvering about 100–200 feet above ground, northbound toward high tension power lines. Shortly after losing sight, he heard two "whoosh" sounds, then a "boom" about five seconds later, and saw black smoke in that direction.
Local law enforcement reported that the helicopter impacted two single-phase overhead power lines near the accident site.
Personnel Information
The pilot, age 81, held a private pilot certificate with airplane single-engine land, multi-engine land, and instrument airplane ratings, as well as a private pilot certificate for rotorcraft. He had a prior accident on March 5, 2007 (NTSB ID SEA07CA069) in which he failed to maintain clearance from parked farm equipment during landing, with the probable cause being his failure to maintain clearance between the tail rotor and equipment.
A third-class medical certificate was issued June 23, 2011, with a limitation that he must wear corrective lenses for near and distant vision. He reported about 7,500 total flight hours and 50 hours in the previous six months.
Aircraft Information
The five-seat, two-bladed Bell 206B, serial number 2216, was manufactured in 1977 and powered by an Allison 250-C20B engine rated at 420 shaft horsepower. It was maintained under a manufacturer's approved inspection program. The most recent required maintenance inspection was completed on August 8, 2012, at which time the airframe and engine had accrued 10,417 total hours.
Meteorological Information
Recorded data from Billings International Airport, about 24 nautical miles southwest of the accident site, at 0653 indicated wind 230° at 11 knots, visibility 10 statute miles, few clouds at 12,000 feet, temperature 13°C, dew point -2°C, and altimeter 30.07 inHg. Calculated density altitude was about 3,805 feet.
Wreckage and Impact Information
The helicopter impacted a low-level power line and terrain about 10 statute miles north-northeast of Shepherd. The debris field was about 70 feet in diameter and mostly consumed by post-impact fire. The two severed power lines had been repaired before examination and ran directly above the main wreckage; supporting poles were undamaged.
A left rear entry door was near the main wreckage with thermal damage. A main rotor blade tip section and one tail rotor blade section were found about 100 feet away. The fuselage came to rest on a heading of about 217°, and the tail boom at about 312° magnetic. All major structural components were located.
The engine was upright with impact damage to the left induction tube and crush damage to exhaust pipes and freewheeling unit cover. The induction inlet had impact damage to stator blades and the first stage of compressor blades.
The main rotor transmission lay on its side with the mast pointing aft and downhill, with thermal damage. Power cable was wrapped around the mast about 25 times. The swashplate assembly appeared functionally operational when manipulated by hand.
Both main rotor blades remained attached to the mast and could be manipulated in pitch. Both blade grips were fractured consistent with mechanical overload. The downhill blade was mostly deformed by fire, with power line cable remnants near its mid-section; a 2-foot tip section separated. The uphill blade had significant impact damage about one-third outboard of the root.
The tailboom assembly lay on its right side, grossly deformed by thermal damage. The tail rotor gearbox and blade assembly were in position but thermally damaged. One tail rotor blade was fractured near the grip; the remainder was nearby. The other blade was similarly fractured, with its remainder about 100 feet away.
The high-skid landing gear was fractured in multiple locations. Both skid tubes had fractures and thermal damage.
Medical and Pathological Information
An autopsy conducted on May 1, 2013, determined the cause of death as smoke inhalation secondary to fire following the helicopter accident. No significant traumatic injuries were found. Other conditions included hypertensive and atherosclerotic cardiovascular disease. A small area of hemorrhage in the left lateral ventricle was reported; the medical examiner noted it could be associated with hypertensive cardiovascular disease, which may have been a factor contributing to death and the crash.
The pilot had a history of deep venous thrombosis and pulmonary embolism (1994), thyroid surgery (1997), paroxysmal atrial fibrillation and hypothyroidism (2008), and multiple orthopedic surgeries, cataract surgery, and carotid artery surgery (2008). He was on anticoagulation therapy with Warfarin. Toxicology tests detected 16% carbon monoxide in blood and Warfarin in blood and urine. The pilot was medically certified at the time of the accident.
The pilot's son reported that his father complained of chest pain the week before the accident and had a CAT scan on April 25, 2013, which revealed no abnormalities.