Dehavilland DHC-6-300 incident near Peach Springs, Arizona, May 21, 2011
On May 21, 2011 at about 11:00 pm local time, a Dehavilland DHC-6-300, registered N178GC, was involved in an incident during enroute (cruise) near Peach Springs, Arizona (Boulder City Muni airport). It was flown under charter and air-taxi rules (Part 135). No one was hurt; 17 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
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.
Source: NTSB aviation accident database, copy made October 4, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- May 21, 2011 · about 11:00 pm local time
- Place
- Peach Springs, Arizona · Boulder City Muni · map
- Type
- Incident
- Injuries
- No one was hurt; 17 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Dehavilland DHC-6-300 · all DHC-6-300s on the register
- Registration
- N178GC · registry record · serial 697
- Damage
- Not recorded
- Flight
- Flight · charter and air-taxi rules (Part 135)
The NTSB's narrative final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
What happened, in order
- Uncontained engine failure during enroute (cruise) defining event
The NTSB's findings
- cause Aircraft › Aircraft power plant › Engine (turbine/turboprop) › Reduction gear and shaft › Failure
- cause Organizational issues › Development › Manufacture/production › Equipment manufacture › Manufacturer
The aircraft
- Seats: 22
- Landing gear: fixed
- Engine 1: Pratt And Whitney Canada PT6A-27 (turboprop); 0 hours total
- Engine 2: (turboprop); 0 hours total
- Operator: Cortez Fisher LLC
The flight
- Departed from: IGM Peach Springs AZ
- Destination: IGM Peach Springs AZ
- Flight plan: not recorded
Weather at the time
- Light: daylight
- Temperature: 0°F (-18°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 2 | |||
| Passengers | 15 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
About this page
Everything above comes from the NTSB's public accident database: the narrative, probable cause and findings are the NTSB's own words, and the coded tables behind its report (pilot, aircraft, flight, weather, injuries, sequence of events) are written out in plain English. Pilots' ages, home towns and medical details are left out on purpose. The documents and photographs are the NTSB's docket, the folder of records gathered during the investigation, shown as the NTSB released them (the NTSB redacts some personal details first) and listed under the NTSB's own titles. This site's own text never names pilots, passengers or anyone else involved. A preliminary report describes what is known soon after the event and can change; the final report, with the probable cause, usually follows one to two years later and this page is refreshed when it does. Case number ENG11IA032.