Robinson Helicopter CO R66 accident near Philip, South Dakota, October 1, 2011
On October 1, 2011 at about 6:55 pm local time, a 2011 Robinson Helicopter CO R66, registered N266CY, was destroyed in an accident during enroute (cruise) near Philip, South Dakota. It was a personal flight under general aviation rules (Part 91). 1 person was killed. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The in-flight separation of the main rotor mast following a mast bumping event. The reason for the mast bumping event could not be determined due to postaccident damage.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- October 1, 2011 · about 6:55 pm local time
- Place
- Philip, South Dakota · map
- Type
- Accident
- Injuries
- 1 person was killed.
- Weather
- visual conditions (good weather)
- Aircraft
- Robinson Helicopter CO R66, built 2011
- Registration
- N266CY · no longer on the register · serial 0010
- Damage
- Destroyed
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The helicopter was on a cross-country flight when it experienced a separation of the main rotor mast 8 inches below the teeter bolt, and the main rotor blade assembly separated from the flying helicopter. Subsequently, the helicopter impacted terrain and a postimpact fire ensued. Examination of the mast revealed fracture features consistent with overload failure and mechanical damage indicative of mast bumping. An examination of the airframe, engine, and remaining systems revealed no preimpact anomalies. The reason for the mast bumping event could not be determined due to the amount of thermal damage to the wreckage.
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
- Unknown or undetermined during enroute (cruise) defining event
- Aircraft structural failure during enroute (cruise)
- Part(s) separation from AC during uncontrolled descent
- Collision with terrain or object (not controlled flight into terrain) during uncontrolled descent
The NTSB's findings
- cause Aircraft › Aircraft propeller/rotor › Main rotor system › Main rotor head system › Damaged/degraded
- cause Aircraft › Aircraft propeller/rotor › Main rotor system › Main rotor head system › Failure
Pilot
- Certificate: private
- Ratings: multi-engine land; single-engine land; instrument: airplane; rotorcraft: helicopter
- Flight time: 3,600 hours in all; 22 in this make and model; 60 in the last 90 days
- Last flight review: May 5, 2010
- Medical certificate: Class 3 (with waivers/limitations)
- Seat: rgt
- Injury: fatal
The aircraft
- Airframe total time: 120 hours
- Last inspection: 100-hour inspection, June 6, 2011; 83 hours since
- Seats: 5
- Landing gear: fixed
- Engine: Rolls-Royc RR300 (turboshaft); 0 hours total
- Fire on the ground
- Operator: P P & J LLC
The flight
- Departed from: GCC Gillette WY at 5:05 pm
- Destination: ICR Winner SD
- Flight plan: none
Weather at the time
- Light: daylight
- Wind: from 150° at 6 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 84°F (29°C), dew point 39°F (4°C)
- Altimeter: 30.00 inHg
- Observation at 6:55 pm from PHP, 3 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 1 |
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.
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.