NTSB Identification: CHI95LA024.
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Accident occurred Saturday, October 22, 1994 in GRAND FORKS, ND
Probable Cause Approval Date: 06/19/1995
Aircraft: PIPER PA-18, registration: N587PA
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

THE FLIGHT INSTRUCTOR AND STUDENT WERE EN ROUTE BACK TO THEIR HOME BASE AFTER PRACTICING LANDINGS AT A LOCAL AIRPORT. APPROXIMATELY EIGHT MILES FROM THEIR DESTINATION, THE ENGINE BEGAN TO RUN ROUGH. THE PROPELLER BECAME UNATTACHED AND THE ENGINE COMPLETELY STOPPED RUNNING. A FORCED LANDING WAS MADE ON A FIELD WITHOUT FURTHER INCIDENT. POSTACCIDENT EXAMINATION REVEALED THE CRANKSHAFT HAD COMPLETELY FRACTURED. EXAMINATION OF THE CRANKSHAFT REVEALED A FATIGUE FAILURE INITIATING FROM AN OIL TRANSFER TUBE HOLE. THIS ORIGIN HOLE WAS FOUND TO HAVE AN ENLARGED DIAMETER PORTION ABOVE THE SPECIFIED VALUE. EXAMINATION OF THE AIRPLANE'S LOGBOOK REVEALED THIS AIRPLANE WAS INVOLVED IN A PROPELLER STRIKE FOUR YEARS AND 1,220 FLIGHT HOURS PRIOR TO THIS ACCIDENT.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

the fatigue failure of the crankshaft.

Full narrative available

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