NTSB Identification: FTW92FA197.
The docket is stored on NTSB microfiche number 47222.
Accident occurred Friday, July 31, 1992 in CIBOLO, TX
Probable Cause Approval Date: 06/30/1993
Aircraft: BOEING A75, registration: N62552
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

THE COMMERCIAL PILOT HAD BEEN TROUBLESHOOTING A VIBRATION PRESENT IN HIS AIRPLANE FOR THE LAST 10 FLIGHT HOURS. AFTER THE BLADE ANGLES ON THE PROPELLER BLADES WERE REALIGNED HE FLEW THE AIRPLANE TO CHECK THE VIBRATION LEVEL. WHILE ON A LEFT DOWNWIND, THE PROPELLER SEPARATED FROM THE ENGINE AND SEVERED A WING STRUT AND PORTION OF THE LEFT WING. AFTER BOTH OF THE BIPLANE'S LEFT WINGS COLLAPSED, THE AIRPLANE ENTERED A LEFT VERTICAL SPIRAL AND IMPACTED IN AN OPEN PASTURE. SEPARATION OF THE CRANKSHAFT WAS A RESULT OF FATIGUE ORIGINATING IN THE THREADS AT A POSITION NORMALLY IN LINE WITH THE AFT FACE OF THE THRUST NUT. THE THRUST NUT ALSO FAILED IN FATIGUE. NUT CONFIGURATION WAS DIFFERENT FROM THE CONFIGURATION INDICATED IN THE ENGINEERING DRAWING. HOWEVER, IT WAS NOT ESTABLISHED IF THIS WAS A CONTRIBUTING FACTOR TO THE FAILURE. THERE WAS ALSO NO EVIDENCE OF OVER TORQUE DURING INSTALLATION.

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

FAILURE OF THE ENGINE CRANKSHAFT DUE FATIGUE AND THE RESULTANT COLLAPSING OF THE LEFT WING.

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