Piper PA-12 accident near Cokeville, Wyoming, September 6, 1992
On September 6, 1992 at about 3:00 pm local time, a Piper PA-12, registered N78599, was substantially damaged in an accident near Cokeville, Wyoming. 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
FATIGUE FAILURE OF THE CRANKSHAFT. FACTORS INCLUDE NON SUITABLE TERRAIN FOR A FORCED LANDING AND AN IMPROPER PROPELLER.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- September 6, 1992 · about 3:00 pm local time
- Place
- Cokeville, Wyoming · map
- Type
- Accident
- Injuries
- No one was hurt; 2 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Piper PA-12 · all PA-12s on the register
- Registration
- N78599 · no longer on the register · serial 12-3961
- 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 PIPER PA 12 REALIZED THAT HE WAS EXPERIENCING A POWER LOSS WHILE MANEUVERING, LOOKING FOR MISSING SHEEP. HE TURNED TO LOWER, FLATTER TERRAIN. THE ENGINE CONTINUED TO LOSE POWER, SO HE MADE A FORCED LANDING IN UNSUITABLE TERRAIN. THE AIRCRAFT NOSED OVER AFTER TOUCHING DOWN. METALLURGICAL TESTING REVEALED THAT THE CRANKSHAFT HAD EXPERIENCED FATIGUE FAILURE. THE ENGINE HAD BEEN INSTALLED ON A FIELD APPROVAL. THE PROPELLER/ENGINE COMBINATION INSTALLED IN THIS AIRCRAFT HAD NOT BEEN TESTED OR APPROVED FOR THIS, OR ANY OTHER, INSTALLATION.
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; single-engine sea
- Flight time: 861 hours in all; 824 in this make and model; 70 in the last 90 days; 29 in the last 30 days; 821 as pilot in command
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: frt
The aircraft
- Airframe total time: 4,777 hours
- Last inspection: annual inspection, May 16, 1992; 68 hours since
- Maximum gross weight: 1,750 lb
- Seats: 2
- Landing gear: fixed
- Engine: Lycoming O-340-A1A (piston); 0 hours total
The flight
- Departed from: Kemmerer WY at 2:15 pm
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Visibility: 40 statute miles
- Sky: clear
- Temperature: 50°F (10°C), dew point 0°F (-18°C)
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.