Amateur-built STOL CH750 incident near Cassville, Missouri, February 6, 2011
On February 6, 2011 at about 5:15 pm local time, a amateur-built STOL CH750, registered N904MS, suffered minor damage in an incident during enroute (cruise) near Cassville, Missouri. It was a personal flight under general aviation rules (Part 91). No one was hurt; 2 people were on board or involved. The weather was visual conditions (good weather).
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The NTSB's probable cause their words, unchanged
The fatigue failure of the propeller hub retaining bolts due to insufficient clamping force .
Source: NTSB aviation accident database, copy made October 4, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- February 6, 2011 · about 5:15 pm local time
- Place
- Cassville, Missouri · map
- Type
- Incident
- Injuries
- No one was hurt; 2 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Amateur-built STOL CH750
- Registration
- N904MS · registry record · serial 75-7495
- Damage
- Minor damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The airplane was in cruise flight when its propeller separated. The pilot performed a forced landing to a snow-covered field, during which the nose landing gear collapsed causing minor damage. Postaccident metallurgical examination of the crankshaft extension attachment bolts revealed that they had fractured from fatigue due to insufficient clamping force. Dish-shaped washers were installed between the bolt head and extension, and thread locking compound was found trapped under the concave side of the washers. The maintenance manual in effect at the time of the incident called for application of thread locking compound to both the female threads in the crankshaft and to the male bolt threads. However, this procedure has the potential for inadvertently wiping a portion of the thread locking compound that is applied to the bolt onto the face of the propeller extension without the installer knowing, thereby trapping it between the washer and the extension face. In this incident, the torque applied to the attachment bolts at installation was insufficient to squeeze out the thread locking compound from under the washers and compress the washers flat, which would have produced the proper metal-to-metal contact. While the applied torque may have been less than specified, it is also possible that the trapped thread locking compound may have had a hydraulic effect that resisted the clamping force associated with a properly applied torque. In the former case, insufficient clamping force would have been present from the time of installation. In the latter case, clamping force could have lessened over time due to wear at the edges of the washer, compression creep, and wear of the trapped thread locking compound. Since this event, the manufacturer has implemented changes to the maintenance procedures with detailed instructions and warnings to prevent contamination of the crankshaft, propeller hub extension, washers, and bolt faces with thread locking compound. In addition, the design of the hub attachment has been modified to incorporate three 8 millimeter dowel pins between the hub and crankshaft to prevent movement between the propeller extension and crankshaft.
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
- Part(s) separation from AC during enroute (cruise) defining event
- Off-field or emergency landing during emergency descent
- Landing gear collapse during landing (landing roll)
The NTSB's findings
- cause Aircraft › Aircraft propeller/rotor › Propeller system › Propeller hub section › Fatigue/wear/corrosion
- cause Not determined › Not determined › (general) › (general) › Unknown/Not determined
Pilot
- Certificate: private
- Ratings: multi-engine land; single-engine land; instrument: airplane
- Flight time: 1,572 hours in all; 125 in this make and model; 25 in the last 90 days; 5 in the last 30 days; 1,460 as pilot in command
- Last flight review: August 8, 2010
- Medical certificate: Class 3 (without waivers/limitations)
- Seat: left
- Injury: no injuries
The aircraft
- Airframe total time: 125 hours
- Last inspection: condition inspection, March 3, 2012; 90 hours since
- Seats: 2
- Landing gear: fixed
- Engine: Jabiru 3300 (piston); 125 hours total
The flight
- Departed from: 94K Cassville MO at 5:05 pm
- Destination: 94K Cassville MO
- Flight plan: none
Weather at the time
- Light: daylight
- Visibility: 10 statute miles
- Sky: broken clouds at 1,800 ft
- Temperature: 37°F (3°C), dew point 30°F (-1°C)
- Altimeter: 29.90 inHg
- Observation at 5:15 pm from HFJ, 14 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flig | 1 | |||
| Passengers | 1 |
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 docket at the NTSB holds the report as a PDF and the investigation's photographs and documents. This site 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 CEN11IA235.