The National Transportation Safety Board did not travel to the scene of this accident.
Additional Participating Entity:
Federal Aviation Administration / Flight Standards District Office; Renton, Washington
Aviation Accident Final Report - National Transportation Safety Board: https://app.ntsb.gov/pdf
Investigation Docket - National Transportation Safety Board: https://dms.ntsb.gov/pubdms
http://registry.faa.gov/N166DR
Location: Shelton, WA
Accident Number: WPR15LA109
Date & Time: 02/19/2015, 1300 PST
Registration: N166DR
Aircraft: BELL/GARLICK UH 1H
Aircraft Damage: Substantial
Defining Event: Powerplant sys/comp malf/fail
Injuries: 1 None
Flight Conducted Under: Part 137: Agricultural
Analysis
While the helicopter was in a hover and beginning to lift a 3,000-lb agricultural application container, the commercial pilot heard a "loud bang," followed by the low rotor warning horn. Ground crew were below the helicopter, so he pulled away from them, and the helicopter then yawed left. He was able to keep the helicopter level about 5 to 7 ft above ground level, and he then pulled the remaining collective pitch to touch down. The helicopter landed on uneven ground and subsequently rolled over onto its right side.
During postaccident wreckage examination, the engine-to-transmission driveshaft adapter, which is the component between the engine output and the driveshaft, was found broken in multiple pieces. Further examination revealed thumbnail-shaped patterns and progressive crack arrest marks, consistent with fatigue, on the fracture surfaces. The bolt that attached the adapter to the mating coupling set had separated. The fracture surfaces on the bolt were generally flat with progressive crack arrest lines consistent with fatigue cracking. Given the sizes of the fatigue cracking areas on the components, it is likely that the attachment bolt separated first. Vibrations in the assembly caused by the separation of the bolt likely resulted in the numerous fatigue cracks in the driveshaft adapter.
Thirty-four years before the accident, the manufacturer issued a technical bulletin, which addressed an issue with inadequate torque being applied on the attachment bolt during assembly and stated that excessive wear had been noted on the engine-to-transmission driveshaft adapter plug when engines were returned for overhaul. The bulletin noted that the wear resulted in the mating driveshaft adapter bottoming out on the antirotation tangs of the driveshaft adapter plug and causing a false torque of the bolt and wear and reduction gear damage. The bulletin identified a fix that involved reworking the driveshaft adapter spline and applying 160 to 200 inch-lbs of torque on the bolt. However, no evidence was found indicating that the recommended actions had been accomplished. The wear on the driveshaft adapter and mating washer could have been the result of an undertorqued bolt or been related to vibrations in the assembly, which resulted from the fatigue cracking of the bolt.
Probable Cause and Findings
The National Transportation Safety Board determines the probable cause(s) of this accident to be:
The fatigue failure of the engine-to-transmission driveshaft adapter attachment bolt due to the application of inadequate torque on the bolt during assembly.
Findings
Aircraft
Engine/transmission coupling - Fatigue/wear/corrosion (Cause)
Engine/transmission coupling - Failure (Cause)
Organizational issues
Manufacture/production - Manufacturer (Cause)
Factual Information
On February 19, 2015, about 1300 Pacific standard time, a Bell/Garlick UH 1H Helicopter, N166DR, made an emergency landing and rolled over following a loss of engine power while in a hover near Shelton, Washington. Northwest Helicopters, Inc., was operating the helicopter under the provisions of 14 Code of Federal Regulations Part 137. The commercial pilot received minor injuries, the helicopter was substantially damaged. Visual meteorological conditions prevailed, and no flight plan had been filed.
The pilot reported that while in a hover and beginning to lift a 3,000-pound agricultural application container, he heard a loud bang followed by the low rotor warning horn sounding. The pilot pulled away from ground crew as the helicopter yawed to the left. He was able to keep the helicopter level about 5 to 7 ft above the ground when he pulled the remaining collective pitch to touch down. The ground underneath was uneven and the helicopter subsequently rolled over onto its right side.
During the postaccident wreckage examination, the engine to transmission driveshaft adapter (Part Number 204-040-812-3), was found broken in multiple pieces. The driveshaft adapter is the component between the engine output and the driveshaft. The failed components were recovered and sent to the National Transportation Safety Board Materials Laboratory Division for further examination.
The Materials Engineer reported that thumbnail-shaped patterns and progressive crack arrest marks consistent with fatigue were observed on the fracture surfaces. The bolt that attached the driveshaft adapter to the mating coupling set had separated. The fracture surfaces on the bolt were generally flat, with progressive crack arrest lines consistent with fatigue cracking.
Bell Helicopter Alert Service Bulletin No. 204-77-6 dated September 30, 1977, Inspection of Engine Drive Shaft Adapter Bolt, P/N 204-040-813-001 for loss of torque, and Technical Bulletin No. 204-81-18 dated June 10, 1981, Engine Driveshaft Adapter P/N 204-040-812-003 rework, indicated that considerable fretting wear damage had occurred to the engine output adapter plug, P/N 1-030-360-04 when engines were returned for overhaul. Extensive wear will allow the drive shaft adapter, P/N 204-040-812-003, to seat on the anti-rotation tangs of the plug and result in a false torque of bolt, P/N 204-040-813-001. The condition will cause plug wear and reduction gear damage. The fretting wear damage of the plug will be eliminated by maintaining the required torque of 160-200 inch-pounds on bolt, P/N 204-040-813-001. Both bulletins recommend compliance times to minimize fretting wear and damage. (See public docket for more information).
Pilot Information
Certificate: Airline Transport; Commercial
Age: 64, Male
Airplane Rating(s): Multi-engine Land; Single-engine Land
Seat Occupied: Right
Other Aircraft Rating(s): Helicopter
Restraint Used: Lap Only
Instrument Rating(s): Airplane
Second Pilot Present: No
Instructor Rating(s): None
Toxicology Performed: No
Medical Certification: Class 2 With Waivers/Limitations
Last FAA Medical Exam: 03/21/2014
Occupational Pilot: Yes
Last Flight Review or Equivalent:
Flight Time: 16600 hours (Total, all aircraft), 700 hours (Total, this make and model), 15800 hours (Pilot In Command, all aircraft)
Aircraft and Owner/Operator Information
Aircraft Manufacturer: BELL/GARLICK
Registration: N166DR
Model/Series: UH 1H
Aircraft Category: Helicopter
Year of Manufacture: 1995
Amateur Built: No
Airworthiness Certificate: Restricted
Serial Number: 66-16949
Landing Gear Type: Skid;
Seats: 2
Date/Type of Last Inspection: 01/16/2014, AAIP
Certified Max Gross Wt.: 9500 lbs
Time Since Last Inspection:
Engines: 1 Turbo Shaft
Airframe Total Time: 11620.1 Hours at time of accident
Engine Manufacturer: LYCOMING
ELT: Installed, not activated
Engine Model/Series: T53-L-13
Registered Owner: NORTHWEST HELICOPTERS I INC
Rated Power: 1125 hp
Operator: NORTHWEST HELICOPTERS LLC
Operating Certificate(s) Held: Agricultural Aircraft (137); Rotorcraft External Load (133); On-demand Air Taxi (135)
Operator Does Business As:
Operator Designator Code: NTWA
Meteorological Information and Flight Plan
Conditions at Accident Site: Visual Conditions
Condition of Light: Day
Observation Facility, Elevation: KSHN, 269 ft msl
Observation Time: 2136 UTC
Distance from Accident Site: 7 Nautical Miles
Direction from Accident Site: 29°
Lowest Cloud Condition: Scattered / 1500 ft agl
Temperature/Dew Point: 12°C / 9°C
Lowest Ceiling: Overcast / 8000 ft agl
Visibility: 10 Miles
Wind Speed/Gusts, Direction: 10 knots, 230°
Visibility (RVR):
Altimeter Setting: 30.22 inches Hg
Visibility (RVV):
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: Shelton, WA
Type of Flight Plan Filed: None
Destination: Shelton, WA
Type of Clearance: None
Departure Time:
Type of Airspace: Class G
Wreckage and Impact Information
Crew Injuries: 1 None
Aircraft Damage: Substantial
Passenger Injuries: N/A
Aircraft Fire: None
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries: 1 None
Latitude, Longitude: 47.129444, -123.231111
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