Wednesday, March 03, 2021

Loss of Engine Power (Partial): Bell 206L-1 Long Ranger, N32AE; accident occurred March 04, 2020 in Clark, Randolph County, Missouri


Aviation Accident Factual Report - National Transportation Safety Board 

The National Transportation Safety Board did not travel to the scene of this accident.

Additional Participating Entities:
Federal Aviation Administration / Flight Standards District Office; Kansas City, Missouri
Air Evac Lifeteam; O’Fallon, Missouri
Transportation Safety Board of Canada; Gatineau, FN
Rolls Royce; Indianapolis, Indiana 
Bell Helicopter; Fort Worth, Texas

Investigation Docket - National Transportation Safety Board:

Location: Clark, Missouri
Accident Number: CEN20LA113
Date & Time: March 3, 2020, 18:42 Local
Registration: N32AE
Aircraft: Bell 206
Aircraft Damage: Substantial
Defining Event: Loss of engine power (partial)
Injuries: 4 None
Flight Conducted Under: Part 135: Air taxi & commuter - Non-scheduled - Air Medical (Unspecified)

Factual Information

On March 4, 2020, about 1842 central standard time, a Bell 206 L1 helicopter, N32AE, was substantially damaged when it was involved in an accident near Clark, Missouri. The commercial pilot, two crewmembers, and one patient were uninjured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 135 helicopter air ambulance flight.

The pilot reported that during cruise on the patient transfer flight, the helicopter yawed right, the rotor rpm warning light illuminated, and the rpm aural indication sounded. The engine continued to operate but was producing less than 90% power. The pilot reduced collective and turned the helicopter toward a field for a precautionary landing. The helicopter touched down hard and the tail boom sustained substantial damage.

A postaccident examination of the helicopter revealed that a pneumatic line, exhibited a separation near its filter connection. The pneumatic line and filter were shipped to the engine manufacturer for examination, which revealed that the tube was fractured completely through at the toe of the weld between the tube and its filter fitting. Surface smearing was present on sections of the separation; however, the separation exhibited surfaces consistent with fatigue that initiated near the top of the tube.

The tube’s outer diameter surface near the elbow separation exhibited rub damage. A photo of the engine bay showed that a red ribbed hose was present in the engine bay near the tube separation and the ribbed hose exhibited discoloration on its outer surface.

Measurements taken during non-destructive examination revealed that the height of the weld root reinforcement exceeded its component specifications. The remaining tube and weld measurements met their component specifications.

A polished cross-section through the weld on the fitting side fracture revealed the fatigue fracture was located at the toe of the weld, initiating at the approximate intersection of the weld heat affected zone (HAZ) and the weld metal of the tube. There were no material anomalies at the fatigue origin location. The fatigue fracture progressed approximately along the intersection between the HAZ and weld metal near the outer diameter surface before proceeding into the HAZ to the inner diameter surface at this plane of examination. Additionally, the weld and base metal microstructures were consistent with the materials required by the component specifications and energy dispersive x-ray spectroscopy revealed that the tube, fitting, and weld materials also met component specifications.

The outer diameter of the filter housing exhibited depressions and deformations consistent with tool marks.

The line was sectioned near its intact (non-failed) connector weld for a computed tomography (CT) examination, which revealed indications of three voids within that tube weld area. The void indications ranged in diameter from 0.0019 to 0.0026 inch. 

A pneumatic leak check was performed 114.9 hours before the accident flight. The tube was last removed 238.9 hours before the accident flight. A leak in the pneumatic line can cause the engine control system to enter a sub-idle fuel flow condition and result in an engine power loss.

After the accident, the operator examined their fleet of helicopters equipped with Rolls Royce 250-C30 engines and no other pneumatic line leaks were found. According to the engine manufacturer, this was the first occurrence of failure involving this pneumatic line design, which was released in 1998. Since that time, the fleet equipped with the pneumatic line had accumulated a total of 17 million flight hours.

Pilot Information

Certificate: Commercial 
Age: 55, Male
Airplane Rating(s): None
Seat Occupied: Right
Other Aircraft Rating(s): Helicopter 
Restraint Used: 5-point
Instrument Rating(s): Helicopter 
Second Pilot Present: No
Instructor Rating(s): None
Toxicology Performed: No
Medical Certification: Class 2 With waivers/limitations 
Last FAA Medical Exam: May 14, 2019
Occupational Pilot: Yes 
Last Flight Review or Equivalent: February 29, 2020
Flight Time: 5252 hours (Total, all aircraft), 383 hours (Total, this make and model), 4221 hours (Pilot In Command, all aircraft), 7 hours (Last 90 days, all aircraft), 5 hours (Last 30 days, all aircraft), 2 hours (Last 24 hours, all aircraft)

Aircraft and Owner/Operator Information

Aircraft Make: Bell 
Registration: N32AE
Model/Series: 206 L1 
Aircraft Category: Helicopter
Year of Manufacture: 1979
Amateur Built: No
Airworthiness Certificate: Normal
Serial Number: 45327
Landing Gear Type: Skid 
Seats: 4
Date/Type of Last Inspection: February 13, 2020 100 hour 
Certified Max Gross Wt.: 4150 lbs
Time Since Last Inspection: 
Engines: 1 Turbo shaft
Airframe Total Time: 27820.7 Hrs as of last inspection
Engine Manufacturer: Rolls Royce
ELT: C126 installed, not activated 
Engine Model/Series: 250-C30P
Registered Owner:
Rated Power: 650 Horsepower
Operating Certificate(s) Held: On-demand air taxi (135)
Operator Does Business As: 
Operator Designator Code: EVCA

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual (VMC) 
Condition of Light: Night
Observation Facility, Elevation: KCOU,778 ft msl 
Distance from Accident Site: 19 Nautical Miles
Observation Time: 18:54 Local 
Direction from Accident Site: 181°
Lowest Cloud Condition: Clear
Visibility 10 miles
Lowest Ceiling: None
Visibility (RVR):
Wind Speed/Gusts: / 
Turbulence Type Forecast/Actual:  /
Wind Direction:
Turbulence Severity Forecast/Actual:  /
Altimeter Setting: 30.05 inches Hg
Temperature/Dew Point: 9°C / -2°C
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: Kirksville, MO (MU92)
Type of Flight Plan Filed: Company VFR
Destination: Columbia, MO (91MO)
Type of Clearance: None
Departure Time: 18:12 Local
Type of Airspace: 

Wreckage and Impact Information

Crew Injuries: 3 None 
Aircraft Damage: Substantial
Passenger Injuries: 1 None 
Aircraft Fire: None
Ground Injuries: N/A 
Aircraft Explosion: None
Total Injuries: 4 None 
Latitude, Longitude: 39.277221,-92.357498(est)

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