N4035G

HISTORY OF FLIGHTOn October 6, 2016, about 1645 central daylight time, a Fairchild Hiller FH-1100 helicopter, N4035G, was destroyed when it impacted the ground near Lino Lakes, Minnesota, following an in-flight separation of the main rotor assembly. The airline transport pilot and passenger sustained fatal injuries, and the helicopter was destroyed. The helicopter was registered to Helicopter Connection LLC, and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as personal flight. Day visual meteorological conditions prevailed, and no flight plan was filed for the local flight, which originated from the Anoka County-Blaine Airport (ANE), near Minneapolis, Minnesota, about 1620.

According to a pilot-rated passenger who had flown with the accident pilot in the helicopter earlier in the day, the accident pilot had not flown the helicopter for about a year and wanted the passenger to "ride along" as a safety pilot. Both the pilot and passenger performed a preflight inspection of the helicopter, which revealed no anomalies. About 1000, they departed on a 5-minute flight then returned and went to lunch. After lunch, they departed on a local flight, which lasted about 45 minutes. After the flight, the passenger asked the pilot if he wanted help moving the helicopter into the hangar, and the pilot indicated that he may fly the helicopter later.

Later that day, several witnesses saw the helicopter flying in a northerly direction. One witness stated that he observed the helicopter rocking back and forth before it "spun sideways" and "a bunch of parts" departed the helicopter. Some reported hearing a "clunk" sound, and others reported hearing a "pop" sound. One witness saw the main rotor blades "seize," then "snap off," followed by the tail rotor departing the helicopter. The witness stated that the helicopter then "dropped out of the sky." Several of the witnesses saw parts departing the helicopter as it descended to ground contact. PERSONNEL INFORMATIONThe 48-year-old pilot held an airline transport pilot certificate with an airplane multi-engine land rating. He held commercial pilot privileges in airplane single engine land, airplane single engine sea, and rotorcraft-helicopter. The pilot also held a flight instructor certificate with airplane single- and multi-engine and instrument airplane ratings. He held a flight engineer certificate with a turbojet rating. The pilot held a Federal Aviation Administration (FAA) special issuance first class medical certificate, dated August 16, 2016, with limitations for corrective lenses and not valid for any class after February 28, 2017. The pilot reported that he had accumulated 15,000 total hours of flight time and 400 hours of flight time during the six months before the medical exam. The last entry in the pilot's logbook was dated September 4, 2015, which was the date he passed his commercial rotorcraft-helicopter checkride. The pilot accumulated 55.5 hours of total flight experience in helicopters at the time of that entry, of which about 38 hours were in the accident helicopter make and model.

The pilot's helicopter flight instructor reported that, from April 15, 2015, to August 4, 2015, he provided instruction to the pilot in the accident helicopter to prepare him for his checkride to obtain a rotorcraft-helicopter rating. The flight instructor stated that the pilot had some trouble at first in the transition from fixed wing to helicopter and that this is fairly common for high-time fixed-wing pilots, such as the accident pilot. After some time, the accident pilot seemed to handle the transition as well as any other of his students that had previous fixed-wing time.

The instructor stated that he gave the pilot ground instruction on teetering rotor systems. When asked how the pilot responded during training situations that could precipitate mast bumping, the instructor stated that the pilot responded correctly to flight in turbulent conditions. He added that, during power loss simulations, the pilot initially was slow to lower the collective and would allow the nose to drop. Eventually, the pilot demonstrated proper entry into and proficiency in autorotations.

The pilot's helicopter flight instructor reported that all the instruction he provided to the pilot took place near Lake Charles, Louisiana, and, after passing his rotorcraft-helicopter checkride, the pilot trailered the helicopter to the Minneapolis area. During the trip, one of the doors of the helicopter came open and cracked the windshield of the helicopter. According to the flight instructor, the pilot had just completed replacement of the windshield a short time before the accident. AIRCRAFT INFORMATIONThe accident helicopter was issued an FAA standard airworthiness certificate on October 20, 1982, and was certificated for normal category operations. The Allison (Rolls Royce) model M250-C20B engine powered a two-bladed, teetering main rotor system. The engine manufacturer indicated that the rated horsepower for the M250-C20B engine is 420 shaft horsepower. According to the helicopter's type certificate data sheet, the engine had a takeoff power rating of 274 shaft horsepower (hp) for a maximum of 5 minutes, and a maximum continuous power rating of 233 shaft hp. The helicopter had a maximum gross weight of 2,750 lbs and could be configured to accommodate a pilot, another pilot or passenger in the cockpit, and three passengers in the cabin. The helicopter's flight manual had limitations to prohibit acrobatic flight and to avoid abrupt control movements when flying in turbulence. The helicopter's most recent annual inspection was completed on June 18, 2015, at a total time in service of 501.7 hours.

In January 2004, the helicopter manufacturer issued Alert Service Letter 23 - 5. The letter indicated that several instances of internal and external mast corrosion had been discovered even when the mast was properly sealed. The corrective action was to remove the transmission top case, with the mast attached, and ship the assembly to the factory for non-destructive inspections. A special coating was to be applied on the interior surfaces. This process is only approved at the factory and cannot be performed in the field. Subsequent to the initial inspection, this process must be done at each overhaul of the transmission or every 10 years whichever comes first. METEOROLOGICAL INFORMATIONAt 1645, the recorded weather at ANE, about 4 miles southwest of the accident site, included wind from 010° at 6 knots, visibility 10 statute miles, overcast clouds at 6,000 feet; temperature 15°C, dew point 6°C, and an altimeter of 29.95 inches of mercury. AIRPORT INFORMATIONThe accident helicopter was issued an FAA standard airworthiness certificate on October 20, 1982, and was certificated for normal category operations. The Allison (Rolls Royce) model M250-C20B engine powered a two-bladed, teetering main rotor system. The engine manufacturer indicated that the rated horsepower for the M250-C20B engine is 420 shaft horsepower. According to the helicopter's type certificate data sheet, the engine had a takeoff power rating of 274 shaft horsepower (hp) for a maximum of 5 minutes, and a maximum continuous power rating of 233 shaft hp. The helicopter had a maximum gross weight of 2,750 lbs and could be configured to accommodate a pilot, another pilot or passenger in the cockpit, and three passengers in the cabin. The helicopter's flight manual had limitations to prohibit acrobatic flight and to avoid abrupt control movements when flying in turbulence. The helicopter's most recent annual inspection was completed on June 18, 2015, at a total time in service of 501.7 hours.

In January 2004, the helicopter manufacturer issued Alert Service Letter 23 - 5. The letter indicated that several instances of internal and external mast corrosion had been discovered even when the mast was properly sealed. The corrective action was to remove the transmission top case, with the mast attached, and ship the assembly to the factory for non-destructive inspections. A special coating was to be applied on the interior surfaces. This process is only approved at the factory and cannot be performed in the field. Subsequent to the initial inspection, this process must be done at each overhaul of the transmission or every 10 years whichever comes first. WRECKAGE AND IMPACT INFORMATIONThe main wreckage came to rest on its right side about 4 nautical miles and 52° magnetic from ANE, on a heading about 20° magnetic. The area around the main wreckage was discolored and charred, consistent with a postaccident ground fire. The remaining sections of wreckage did not exhibit any evidence of pre- or postimpact fire.

The initial piece of wreckage was a section of composite material located about 1,675 ft south of the main wreckage. A debris path extended to the main wreckage and contained the floor mats, a section of white interior material, an exhaust stack, exhaust duct, a section of the tailboom, the engine cowl, a section of exterior metal with the rotating beacon, a seat cushion, and a section of the tail, including the tail rotor and its gearbox. The separated main rotor blades and hub were found east of this debris path in a pond about 500 ft south of the main wreckage. All major components were accounted for at the scene.

The main wreckage, consisting of the cockpit and cabin, was destroyed by impact and postimpact fire. Cyclic, collective, and tail rotor control continuity could not be established due to substantial damage to the cockpit and cabin areas. However, all observed control discontinuities were consistent with overload or thermal damage.

The engine, transmission, and tail rotor driveshafts exhibited separations. All observed separations were consistent with torsional overload and overload. Circumferential witness marks were observed on the exterior of the tail rotor driveshaft.

The main transmission exhibited...