Diamond Aircraft Industries 20C-1 incident near Spanish Fork, Utah, July 1, 2000
On July 1, 2000 at about 7:00 pm local time, a Diamond Aircraft Industries 20C-1, registered N991CT, suffered minor damage in an incident near Spanish Fork, Utah. 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 company maintenance personnel's inadequate torquing procedures of the propeller attachment bolts which resulted in the fatigue failure of the propeller attachment bolts and the in-flight separation of the propeller.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 1, 2000 · about 7:00 pm local time
- Place
- Spanish Fork, Utah · map
- Type
- Incident
- Injuries
- No one was hurt; 2 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Diamond Aircraft Industries 20C-1
- Registration
- N991CT · no longer on the register · serial C0091
- Damage
- Minor damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The pilot had just departed on a cross-country flight, and had climbed to 9,500 feet. He said that he began to feel a 'heavy vibration' in the aircraft, and immediately turned towards the closest runway. Soon thereafter the propeller separated from the airplane, and the pilot performed a forced landing without further incident. Postincident examination of the maintenance records indicated that the attachment bolts for the wooden propeller were last torqued 110 hours before the incident. The manufacturer of the propeller recommends that their wooden propellers be torque checked every 50 hours of flight. Examination revealed that the propeller attachment bolts showed signs of fatigue failure. There was also fretting damage on the propeller extension flange and bushing shanks. The above-mentioned signatures are suggestive of the studs being insufficiently torqued by the mechanic during assembly or periodic maintenance procedures not being followed, and subsequently becoming loose during propeller operation.
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: single-engine land
- Medical certificate: Unknown
- Seat: left
The aircraft
- Last inspection: continuous airworthiness programme
- Maximum gross weight: 1,720 lb
- Seats: 2
- Landing gear: fixed
- Engine: Continental IO-240 (piston); 0 hours total
The flight
- Departed from: PVU Provo UT at 6:45 pm
- Destination: 41U Ephraim UT
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Wind: from 200° at 10 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 84°F (29°C), dew point 39°F (4°C)
- Altimeter: 30.00 inHg
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 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.