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).
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 November 2, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- February 6, 2011 · about 5:15 pm local time · cases in 2011
- 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 | |
|---|---|---|---|---|
| Flight crew | 1 | |||
| Passengers | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
9 documents, released by the NTSB on November 14, 2013. View them here, or download them; the NTSB redacts some personal details before release, and this site shows the NTSB's own titles rather than its file names.
| # | Document | What it is | |
|---|---|---|---|
| 1 | Materials Laboratory Factual Report 11-113 (10 Photos) | PDF, 6 pages | View Download |
| 2 | Materials Laboratory 15 - Factual Report 11-113B with Photos) | PDF, 7 pages | View Download |
| 3 | Pilot/operator Aircraft Accident Report, NTSB Form 6120.1 | PDF, 9 pages | View Download |
| 4 | Record of Conversation with Pilot | PDF, 1 page | View Download |
| 5 | Engine Overhaul Manual Excerpt in Effect at Time of Incident | PDF, 3 pages | View Download |
| 6 | Jabiru Service Bulletin JSB022-1 | PDF, 4 pages | View Download |
| 7 | Propeller Installation Instructions | PDF, 4 pages | View Download |
| 8 | Letter from Engine Manufacturer's Representative | PDF, 1 page | View Download |
| 9 | Evidence Control Form | PDF, 8 pages | View Download |
The same docket at the NTSB · documents without a copy here are fetched from the NTSB when you open them.
Connections how this case links to the rest of the register
- N904MS on the register today · the tail number may have moved to another aircraft since
- Engine: Jabiru 3300 475 aircraft carry this series today · as the NTSB recorded it
- Cassville Municipal · departed from
- Accidents and incidents in Missouri 1,640 since 1982 · 219 in the last ten years
- Missouri 5,817 aircraft registered
The whole map of how records connect · these connections as data: /graph/accident/CEN11IA235.json.
The bigger picture in Aviation Analytics: accidents over time since 1982, by model, by phase of flight and conditions, by place and on the map.
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 does not name anyone involved, its policy at this time. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.