Friday, April 26, 2019

AgustaWestland AW139, registered to and operated by Chevron USA Inc under the provisions of Title 14 Code of Federal Regulations Part 91 as business flight, N639NA: Accident occurred April 07, 2016 in Galliano, Louisiana

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

Additional Participating Entities:

Federal Aviation Administration / Flight Standards District Office; Jackson, Mississippi
Italian Safety Investigation Authority, ANSV; FN
Leonardo Helicopters; FN
Leonardo Helicopters

Aviation Accident Factual 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/N639NA

Location: Galliano, LA
Accident Number: CEN16LA401
Date & Time: 04/07/2016, CDT
Registration: N639NA
Aircraft: AGUSTAWESTLAND PHILADELPHIA AW139
Aircraft Damage: Substantial
Defining Event: Part(s) separation from AC
Injuries: 9 None
Flight Conducted Under: Part 91: General Aviation - Other Work Use 

HISTORY OF FLIGHT

On April 7, 2016, at an unknown time, an AgustaWestland AW139 helicopter, N639NA, sustained damage to a main rotor blade during a flight over the Gulf of Mexico. The pilot, co-pilot, and 7 passengers were not injured, and the helicopter sustained substantial damage. The helicopter was registered to and operated by Chevron USA Inc., under the provisions of Title 14 Code of Federal Regulations Part 91 as business flight. Visual meteorological conditions prevailed for the flight and a company visual flight rules (VFR) flight plan had been filed. The flight originated at 0600 from South Lafourche Leonard Miller Jr. Airport, (GOA), Galliano, Louisiana, with an en route stop at an oil rig in the Gulf of Mexico and terminated at GOA about 1135.

On May 9, 2018, the Chevron aviation department reported the accident to the NTSB and stated that during the flight the crew felt a slight vibration of the tail rotor. After landing at GAO during a post flight inspection, one of the tail rotor blade (TRB) erosion shield extensions (figure 1) commonly known as a lightning strip (LS) was missing and only its side tabs remained attached to the blade. Additionally, a main rotor blade (MRB) tip was damaged.


Figure 1 – TRB erosion shield extension diagram with notations (Courtesy of Leonardo)

PERSONNEL INFORMATION

AIRCRAFT INFORMATION

The separated LS was identified as part number (p/n) 3G6410L00152 that was manufactured in electroplated nickel.

Chevron reported that as a normal maintenance practice, an LS would be installed as a brand new part or as an "on-condition" item that had been installed at the discretion of the company maintenance personnel after the component was inspected and determined to be in airworthy condition.

Chevron reported that the associated tail rotor blade (TRB) was received new from Leonardo on May 22, 2015, without an LS installed. An LS was subsequently installed by Chevron with no serial number tracking requirement.

On January 30, 2016, the white TRB was removed and replaced due to wear on the main erosion shield from contact with the LS. The same LS was reinstalled on the replacement white TRB.

From February 26, 2016, to April 6, 2016 the helicopter accumulated 129.1 flight hours with the new TRB installed. During that time, 34 daily serviceability checklist inspections were completed and no discrepancies applicable to the LS on the white TRB (or any other TRB) were noted.

METEOROLOGICAL INFORMATION

WRECKAGE AND IMPACT INFORMATION

A Chevron post flight inspection of the helicopter revealed that the LS on the white TRB was fractured and most of the component was missing. Only the side tabs, where the tail rotor damper bracket bushings pass through, remained attached (figure 2).


Figure 2 – Damaged Tail Rotor Erosion Shield Extension (Courtesy of Chevron)

The inspection also found damage to one of the main rotor blades; the blue MRB tip sustained damage mostly on the under side of the blade (figure 3). No additional damage was observed on the remainder of the helicopter.


Figure 3 – Damaged Main Rotor Blade (Courtesy of Chevron)

TESTS AND RESEARCH

Failure Analysis

Leonardo, the current AW139 helicopter manufacturer, performed a failure analysis on the remaining portion of the LS, using a scanning electron microscope (SEM), which revealed the presence of microcavity spots or porosity on the surface of the fractured section (figure 4). In the figure, the area circled in yellow is the microcavity, the red dashes indicate the crack initiation, and the blue arrows indicate the direction of the fatigue crack propagation.


Figure 4 – SEM image of the fatigue propagation from a micro-cavity, yellow circle (Courtesy of Leonardo)


Figure 5 shows a wide view of the fracture surface with the crack origination circled in red.

Figure 5 – SEM image, wide view of fracture surface (Courtesy of Leonardo)

Static Testing

Finite element modeling (FEM) of an exemplar LS was completed to determine the expected inflight stress values, to include the influence of the centrifugal force and the bending moment due to the deformation of the TRB under beam bending loads. The simulation showed that the maximum stress values in the crack initiation area were considerably lower than the fatigue limit specified for the electroplated nickel material. Of note, the FEM model considered the geometric and fitting stress concentrations without the presence of a material flaw (such as a microcavity).

Flight Testing

A flight test was performed to evaluate the load conditions of the LS during flight. Strain measurement instrumentation was installed on a Leonardo helicopter to monitor and record the load conditions. Test results did not reveal any particular load condition that could lead to similar LS failures experienced during the accident flight.

ADDITIONAL INFORMATION

Related Events

Leonardo identified 6 additional events involving the same LS part number and the three scenarios are listed below. Of note, all three scenarios resulted in an uneventful landing.

LS crack identified during scheduled inspections (3 events)
LS fractured and separated in flight (2 events)
LS fractured and separated inflight, which resulted in damage to MRB tip (2 events, including the accident flight)

Corrective Actions

In response to the reports of similar LS failures, Leonardo changed the specification from electroplated nickel to a higher strength steel. As of July 31, 2017, for all newly built helicopters, the TRB installation drawing was updated to prescribe the installation of a steel LS, p/n 3G6410A03053, (figure 6). Additionally, Leonardo will issue an optional service bulletin to provide the steel LS upon customer request.


Figure 6 – Diagram of the updated steel LS (left) and electroplated nickel LS (right)

Pilot Information

Certificate: Airline Transport
Age: 52, Male
Airplane Rating(s): None
Seat Occupied: Right
Other Aircraft Rating(s): Helicopter
Restraint Used: 4-point
Instrument Rating(s): Helicopter
Second Pilot Present: Yes
Instructor Rating(s): Helicopter
Toxicology Performed: No
Medical Certification: Class 1 Without Waivers/Limitations
Last FAA Medical Exam: 02/19/2016
Occupational Pilot: Yes
Last Flight Review or Equivalent: 10/31/2015
Flight Time:  14500 hours (Total, all aircraft), 1250 hours (Total, this make and model), 12000 hours (Pilot In Command, all aircraft), 125 hours (Last 90 days, all aircraft), 35 hours (Last 30 days, all aircraft), 6 hours (Last 24 hours, all aircraft) 

Co-Pilot Information

Certificate: Airline Transport
Age: 35, Male
Airplane Rating(s): Single-engine Land
Seat Occupied: Left
Other Aircraft Rating(s): Helicopter
Restraint Used: 4-point
Instrument Rating(s):
Second Pilot Present: Yes
Instructor Rating(s): Helicopter; Instrument Helicopter
Toxicology Performed: No
Medical Certification: Class 1 Without Waivers/Limitations
Last FAA Medical Exam: 03/20/2016
Occupational Pilot: Yes
Last Flight Review or Equivalent: 10/31/2015
Flight Time:  5792 hours (Total, all aircraft), 1813 hours (Total, this make and model), 2866 hours (Pilot In Command, all aircraft), 114 hours (Last 90 days, all aircraft), 32 hours (Last 30 days, all aircraft), 6 hours (Last 24 hours, all aircraft)

Aircraft and Owner/Operator Information

Aircraft Make: AGUSTAWESTLAND PHILADELPHIA
Registration: N639NA
Model/Series: AW139
Aircraft Category: Helicopter
Year of Manufacture: 2013
Amateur Built: No
Airworthiness Certificate: Transport
Serial Number: 41326
Landing Gear Type: Emergency Float; Tricycle
Seats: 14
Date/Type of Last Inspection: 04/06/2016, Continuous Airworthiness
Certified Max Gross Wt.: 14991 lbs
Time Since Last Inspection:
Engines: 2 Turbo Shaft
Airframe Total Time: 2497.8 Hours at time of accident
Engine Manufacturer: P&W CANADA
ELT: C126 installed, not activated
Engine Model/Series: PT6C-67C
Registered Owner: CHEVRON USA INC
Rated Power: 1531 hp
Operator: CHEVRON USA INC
Operating Certificate(s) Held: On-demand Air Taxi (135)
Operator Does Business As:
Operator Designator Code: AC2A 

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual Conditions
Condition of Light: Day
Observation Facility, Elevation: KXPY, 99 ft msl
Distance from Accident Site: 19 Nautical Miles
Observation Time: 0915 CDT
Direction from Accident Site: 170°
Lowest Cloud Condition:
Visibility:  10 Miles
Lowest Ceiling: 
Visibility (RVR):
Wind Speed/Gusts: 7 knots /
Turbulence Type Forecast/Actual:
Wind Direction: 340°
Turbulence Severity Forecast/Actual: /
Altimeter Setting: 30.03 inches Hg
Temperature/Dew Point: 22°C / 12°C
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: GALLIANO, LA (GAO)
Type of Flight Plan Filed: Company VFR
Destination: Galliano, LA (GAO)
Type of Clearance: None
Departure Time: 0600 CDT
Type of Airspace: Class E; Class G

Airport Information

Airport: SOUTH LAFOURCHE LEONARD MILLER (GAO)
Runway Surface Type: N/A
Airport Elevation: 0 ft
Runway Surface Condition: Unknown
Runway Used: N/A
IFR Approach: None
Runway Length/Width:
VFR Approach/Landing: None

Wreckage and Impact Information

Crew Injuries: 2 None
Aircraft Damage: Substantial
Passenger Injuries: 7 None
Aircraft Fire: None
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries: 9 None
Latitude, Longitude: 29.438056, -90.262500 (est)

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