Amateur-built Moni accident near Laurel, Montana, July 12, 2002
On July 12, 2002 at about 4:20 pm local time, a amateur-built Moni (glider), registered N9104S, was substantially damaged in an accident near Laurel, Montana. It was a personal flight under general aviation rules (Part 91). No one was hurt; 1 person was on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
Undertorqued mounting bolts which resulted in fatigue to the wooden propeller blade and subsequent in flight separation of one of the blades while in cruise flight. An improper installation of the propeller assembly and soft terrain encountered during the landing roll were factors.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 12, 2002 · about 4:20 pm local time
- Place
- Laurel, Montana · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Amateur-built Moni
- Registration
- N9104S · registry record · serial PJT-00048
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The pilot of the homebuilt aircraft and installer of the wooden propeller assembly reported that during a performance test/rate of climb test with the new propeller, he smelled a wood burning smell followed by a "real bad vibration." The pilot initiated a forced landing to an open field. During the landing roll on the soft terrain, the landing gear sheared off. After the accident, the pilot noted that one of the blades of the wooden propeller was missing. The remaining blades and two hub plates were sent to the NTSB Materials Laboratory for examination. The metallurgist reported that the fretting observed on the hub plates suggested that the hub mounting bolts were not as tight as required allowing the hub to oscillate on its mounting flange. The motion in the pitch block of both blades produced the heat that charred the wood and softened the pitch block material allowing it to be displaced and imprinted with the pattern of the wood plies. The compression failure and the frictional features on the hub portion in the pitch block indicated a fatigue-like failure in wood which propagated until the remaining wood could not withstand the stresses of operation and subsequently failed in a tensile mode.
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
Pilot
- Certificate: private
- Ratings: multi-engine land; single-engine land; instrument: airplane; rotorcraft: glider
- Flight time: 1,218 hours in all; 145 in this make and model; 16 in the last 90 days; 5 in the last 30 days; 1,073 as pilot in command
- Last flight review: May 30, 2002
- Medical certificate: Class 3 (valid medical--w/ waivers/lim.)
- Seat: ctr
- Injury: no injuries
The aircraft
- Airframe total time: 151 hours
- Last inspection: annual inspection, June 2, 2002; 5 hours since
- Maximum gross weight: 560 lb
- Seats: 1
- Landing gear: fixed
- Engine: Komet KFM107E (piston); 0 hours total
The flight
- Departed from: 6S8 Laurel MT at 4:00 pm
- Flight plan: none
Weather at the time
- Light: daylight
- Wind: from 270° at 5 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 82°F (28°C), dew point 45°F (7°C)
- Altimeter: 30.06 inHg
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| 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.