History of Flight
On June 19, 2013, at 0812 central daylight time, a Bell 47G-3B-1 single-engine helicopter, registration N5024N, impacted a residential garage while maneuvering near Maplewood, Minnesota. The commercial pilot, the sole occupant, sustained fatal injuries. The helicopter was destroyed by impact and post-crash fire. The helicopter was registered to and operated by Scott's Helicopter Services, Inc., Le Sueur, Minnesota, under 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed, and the flight operated without a flight plan. The flight originated from a remote staging area at 0755.
According to the operator and global positioning system data, the helicopter departed Flying Cloud Airport, Minneapolis, at 0716 and flew to a remote staging area near Maplewood to be loaded with a mosquito control dry chemical. The helicopter was loaded with 640 pounds of dry chemical and departed the staging area. The pilot planned to apply chemical to four designated areas. GPS data showed the helicopter maneuvered around two of the areas, consistent with chemical application, and then transitioned north-northeast. The helicopter maintained a level altitude of approximately 200–300 feet above ground level. In the last 30 seconds of the flight, groundspeed gradually increased from 49 to 67 knots. The last recorded GPS position placed the helicopter at 300 feet AGL, groundspeed 67 knots, heading 15 degrees, about 400 feet south of the accident location.
A witness observed the helicopter applying chemical at one designated area south of the staging area, then departing. Other witnesses near the accident location saw the helicopter traveling south to north. Prior to impact, the helicopter lost altitude, turned or rolled left, and descended. Witnesses lost sight behind houses.
Personnel Information
The pilot held a commercial pilot certificate with rotorcraft-helicopter and instrument helicopter ratings. The most recent second-class medical certificate was issued December 11, 2012, with no restrictions. The most recent flight review was completed by Scott's Helicopter Services, Inc., on April 23, 2013. The pilot had approximately 2,794 flight hours, including 2,778 in helicopters and 332 hours in the accident make and model.
The pilot had previously worked for Scott's Helicopter Services from April to October 2009 conducting mosquito control, pipeline patrol, and electronic news gathering operations. From December 2009 to April 2013, the pilot worked in helicopter emergency medical services. The pilot returned to Scott's Helicopter Services in April 2013 and had flown about 100 hours in the accident make and model performing mosquito control since returning.
Family members reported the pilot was in excellent health and well-rested preceding the accident. A company pilot who interacted with the accident pilot on the morning of the accident stated the accident pilot arrived at the Flying Cloud hangar around 0620, made coffee, checked weather, and both pilots preflighted their helicopters. After departure, the company pilot had no further communication.
Aircraft Information
The accident helicopter was a Bell 47G-3B-1, serial number 6601, equipped with a Rolls Royce 250-C10D turboshaft engine per a supplemental type certificate. The helicopter received a special airworthiness certificate in the restricted category for Agricultural and Pest Control on April 19, 1991, and was registered to the owner on June 10, 1994. The most recent annual and 100-hour inspections were completed December 14, 2012, at total airframe time 5,340.3 hours and total engine time 2,948.8 hours. Additional 200-, 300-, and 400-hour airframe inspections and 200- and 300-hour engine inspections were also completed on that date.
Meteorological Information
At 0753, the Saint Paul Downtown Airport automated surface observing system, located 4 miles southwest of the accident site, reported wind from 140 degrees at 8 knots, visibility 10 miles, sky clear, temperature 18°C, dew point 13°C, and altimeter 30.07 inches of mercury.
Wreckage and Impact Information
The helicopter impacted a residential garage and came to rest on its left side on a measured magnetic heading of 275 degrees. The cockpit and fuselage were consumed by post-impact fire. Debris, including windscreen and fiberglass sections, was distributed over an area about 100 feet in diameter. Ground scars and impact marks consistent with main rotor blades were found on the driveway and garage roof. The garage was partially consumed by fire.
Both main rotor blades remained attached to the hub with leading edge crush damage, bending, twisting, and fragmentation. Mechanical continuity was confirmed from engine through transmission and main rotor blades. The tail rotor drive shaft was disconnected from the engine. Main rotor pitch links were intact, but continuity from cockpit controls could not be established due to fire damage. The main rotor clutch assembly was intact and functioned normally.
The tailboom remained partially attached. The tail rotor drive system was bent and distorted; continuity could not be established due to separated components. Damage to the tail rotor system was consistent with impact. Tail rotor blades remained attached; one was bent spanwise 45 degrees near the grip, the other bent 90 degrees at the grip. Mechanical continuity to the blades was confirmed through the gearbox and pitch control assembly. Tail rotor pitch control cables were separated with broomstraw features consistent with tensile overload.
The engine remained partially attached with thermal damage. Left engine mounts fractured; right mounts bent and fractured. Exhaust collector and ductwork crushed. Engine fuel spray nozzle removed for borescope examination of the gas-generator turbine; no evidence of turbine distress, erosion, or failure. Metal splatter noted on the 1st stage turbine nozzle shield. Fuel spray nozzle screen clear. Upper magnetic chip detector clear; lower chip detector showed small amount of metallic paste and carbonized oil but no metallic debris. Engine oil filter contained some carbonized oil but no metallic debris.
Fuel tanks displayed thermal damage and remained partially attached. Landing skids bent, deformed, and fragmented. Chemical hopper assemblies separated, fragmented, and partially consumed by fire.
Flight and engine instruments consumed by fire; no recognizable information. Annunciator panel light bulbs showed no filament stretch. Collective throttle found in open position. Cockpit seats and restraints consumed by fire.
A portable Garmin GPSMAP 296 and an AG-NAV GPS unit were sent to the NTSB Vehicle Recorders Laboratory for data extraction.
Medical and Pathological Information
An autopsy was performed on June 19, 2013, at the Ramsey County Office of the Medical Examiner. Toxicological analysis at the FAA Toxicology and Accident Research Laboratory tested for cyanide, ethanol, volatiles, and drugs; none were found. Carbon monoxide testing could not be performed due to insufficient specimen.
Tests and Research
AG-NAV GPS Unit: The AG-NAV unit sustained major fire damage. The CF card containing flight log data was melted to the unit and could not be recovered.
Garmin GPSMAP 296 Unit: The Garmin unit sustained minor impact damage to the casing. It powered on normally and data was extracted. Three sessions from the accident day were recovered, totaling 279 data points. The accident flight was recorded from 0755:24 to 0812:01 (179 data points). The flight from Flying Cloud Airport to the remote staging field was recorded from 0716:28 to 0744:51.
Engine Examination: On November 5, 2013, at Rolls Royce facilities, the engine was examined and disassembled under NTSB supervision. The 1st stage compressor blades showed foreign object damage with tearing and bending opposite normal rotation. The compressor could not be rotated due to melting and deformation of polymer lining in compressor case halves. An air pressure check of engine control systems could not be completed due to damaged pneumatic tubing. The fuel control unit's mounting lugs and drive shaft were fractured; the stub remnant could be rotated by hand; microscope examination showed the drive shaft fractured in linear overload. The engine-driven fuel pump drive shaft rotated by hand. Metal splatters on the 1st stage turbine nozzle shield were consistent with impact damage to the compressor. The gas generator turbine rotated by hand with no binding or drag. The power turbine shaft-to-pinion gear coupling exhibited a 2–3 mm bulge at its midpoint, consistent with rotational contact and frictional heating from bending movement during impact. Rotational witness marks were noted within the 4th stage turbine air seal. The turbine-to-compressor coupling showed circumferential scoring on the outer surface. The compressor diffuser scroll was removed; the front diffuser exhibited rotational scoring consistent with contact by the centrifugal compressor rotor during operation.
Weight and Balance
The most recent weight and balance form indicated a useful load of 1,061 lbs. The pilot weighed approximately 163 lbs. Estimated fuel on board was 35 gallons, and estimated chemical was 600 lbs. The total weight of pilot, fuel, and chemical would result in the helicopter being about 54 lbs less than the maximum gross weight of 2,950 lbs.