History of Flight
On December 2, 2014, about 1400 mountain standard time, a Robinson R44 II helicopter, registration N3234U, impacted a two-story building while maneuvering near Skypark Airport (BTF) in Bountiful, Utah. The commercial pilot/mechanic and passenger were fatally injured, and the helicopter was substantially damaged. The helicopter was registered to Native Range Capture Services, Inc., Elko, Nevada, and operated by Native Range, Inc., Ventura, California. Visual meteorological conditions prevailed, and no flight plan was filed for the local post-maintenance test flight conducted under 14 CFR Part 91. The flight departed from BTF shortly before the accident.
According to the helicopter owner, the pilot/mechanic had been performing maintenance on the main rotor assembly, and the purpose of the flight was to track and balance the main rotor blades, a procedure that spanned several days.
Several witnesses heard popping or banging sounds and saw the main rotor and empennage separate from the helicopter. The helicopter tumbled and struck the top of a building. The separated components came to rest a few hundred feet away. Security camera footage captured the helicopter after separation.
Personnel Information
The pilot, age 65, held a commercial pilot certificate with rotorcraft, airplane single-engine land, multi-engine land, and instrument ratings. He held a second-class medical certificate issued April 1, 2014, with no limitations. He reported 5,500 total flight hours. He also held a mechanic certificate with airframe and powerplant ratings and had attended Robinson Helicopter Company's maintenance course in 2008.
The passenger, age 63, held a private pilot certificate with a rating for airplane single-engine land and a third-class medical certificate issued October 26, 2006, with limitations requiring glasses for near vision. He reported 250 total flight hours and held a mechanic certificate with airframe and powerplant ratings. He had not attended Robinson's maintenance course.
Aircraft Information
The four-seat helicopter was manufactured in February 2007, powered by a Lycoming IO-540-AE1A5 engine rated at 205 horsepower.
The owner stated that during a flight the month before, the helicopter had noticeable vertical vibrations, and the blades had slop in the pitch change link bolt attachment. During a 100-hour inspection on November 2, 2014, at 582 total hours, the owner and pilot/mechanic recommended sending the blades for rework. The red main rotor blade pitch horn was replaced, and the pilot-rated mechanic declined repainting. Upon their return, the owner hired the pilot-rated mechanic to install the blades and track them.
A mechanic who spoke with the pilot weeks before reported discussion about an elongated pitch change link attachment hole. The night before the accident, the pilot said he was having trouble tracking the blades, could not get better than a 1/2-inch separation, and was using trim tabs. The mechanic suggested fine adjustments and inspecting the entire rotor system.
Maintenance records showed that on September 12, 2007, at 87.3 hours, the hub and blades were rebuilt by Robinson, with spindles reused.
Meteorological Information
At 1353, the weather observation at Salt Lake City International Airport (SLC), 5 miles south, reported wind from 320° at 3 knots, visibility 10 statute miles, scattered clouds at 15,000 feet, broken clouds at 19,000 feet, temperature 8°C, dew point 2°C, and altimeter 30.05 inHg.
Wreckage and Impact Information
Examination revealed a debris field about 880 ft long and 400 ft wide oriented 277° magnetic. The main rotor and empennage separated before impact. The main rotor assembly was found 188 ft from the main wreckage; the empennage, 430 ft. Tail rotor drive shaft sections were scattered; a large section pierced a roof 90 ft from the fuselage impact. Both pitch change links and transmission material were found throughout. A 4-ft main rotor blade tip was in a retention pond.
The main wreckage penetrated the roof of a two-story building about 2,000 ft southwest of runway 34 at BTF. A postimpact fire occurred but was limited by the building's sprinkler system. The cabin was crushed and distorted. Flight controls had overload separations. The engine remained attached; thermal damage was noted. The main rotor gearbox separated at the housing; the mast tube fractured.
The red blade remained attached to the hub but separated outboard; the blue blade remained attached but had impact marks. Pitch horns fractured; pitch change links had multiple bends and fractures. Pitch change link attachment hardware was missing or had low torque. Hub and swashplate showed impact marks consistent with flapping exceedance.
Medical and Pathological Information
Postmortem examinations by the Utah Department of Health reported cause of death for both occupants as total body blunt force injuries. Toxicology tests for the pilot were negative for carbon monoxide, cyanide, volatiles, and drugs.
Tests and Research
Components sent to the NTSB Materials Laboratory showed all fractures were overstress, with no preexisting cracking. The red blade pitch change link attachment hole was intact. Missing hardware included counterweights and lower attachment hardware. Torque measurements on three recovered attachment bolts were lower than manufacturer's specifications (240 lb-in ± 24 lb-in for locknuts, 20-40 lb-in for palnuts).