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NTSB Report
September 6, 1992 · Piper PA-12 · N78599
Cokeville, WY
Overview
Report Status
Probable Cause
Event Type
Accident
Date
September 6, 1992
Injury Outcomes
No injuries (2 uninjured)
Location
Cokeville, WY
Aircraft
Piper PA-12
Tail Number
N78599
Operator
John I Ritter
Injuries
None
Aircraft Damage
Substantial
NTSB Number
SEA92LA196
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.
NTSB Probable Cause
FATIGUE FAILURE OF THE CRANKSHAFT. FACTORS INCLUDE NON SUITABLE TERRAIN FOR A FORCED LANDING AND AN IMPROPER PROPELLER.
Full Narrative
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.
Flight
Event TypeAccident
Event Time09:00 MDT
Nearest Airport0nm N
Runway0
Flight Plan FiledNone
Aircraft FireNo
Aircraft ExplosionNo
Aircraft
AircraftPiper PA-12
Tail NumberN78599
Aircraft CategoryAir
DamageSubstantial
OperatorJohn I Ritter
Operating RulePart 91
Engines1
Engine TypeReciprocating
Engine DetailsLycoming · O-340-A1A · Reciprocating · 170
Seats2
People & Injuries
Injury SummaryNo injuries (2 uninjured)
Fatal0
Serious0
Minor0
Uninjured2
Total2
Crew 1Age 51 · Second Class
Conditions
ConditionsVMC
LightDaylight
WindCalm
Visibility40 sm
CeilingNone
Temperature / Dew Point50 / 0 C
Altimeter0
Weather SourcePILO