DEHAVILLAND DHC-6-300 near Peach Springs, AZ — 2011-05-21
- Date
- 2011-05-21
- Location
- Peach Springs, AZ, USA
- Airport
- BVU
- Aircraft
- DEHAVILLAND DHC-6-300
- Registration
- N178GC
- Category
- Airplane
- Highest injury
- None
- Fatalities
- 0
- Phase of flight
- Cruise
Probable cause
A quality control failure in the Sungear, Inc. manufacturing and quality control process allowed sungears with surface finishes of the root fillet radius of the spline that did not conform to the drawing specifications to be released. The surface finish defect caused fatigue cracks to initiate early in the part life.
NTSB narrative
The 1st stage planetary gear assembly was examined by the NTSB laboratory in Washington, DC, and a Materials Laboratory Factual Report, No. 12-100A was issued. A summary of the NTSB laboratory report findings is as follows: The average surface roughness of the root fillet radius surface of the sungear measured 22.68 micro-inches, which is coarser than 8 micro- inches, maximum, specified in the sungear engineering drawing. The fractures of the sungear was the result of a fatigue crack that emanated from the coarse surface finish within the root fillet radius portion of the sungear. The gears were not manufactured in accordance with the engineering drawing. A quality control failure in the Sungear, Inc. manufacturing and quality control process allowed sungears with incorrect surface finishes of the root fillet radius of the spline to be released.
Analysis
- Primary failure mode
- Mechanical failure
- First missed decision gate
- Use of non-OEM parts in engine maintenance could have been reconsidered.
NTSB coding
- Uncontained engine failure · Enroute-cruise
Evidence available
- 5 docket documents
Docket documents5
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