NTSB Identification: ATL90LA173.
The docket is stored on NTSB microfiche number 44598.
Accident occurred Thursday, September 20, 1990 in HERTSBORO, AL
Probable Cause Approval Date: 02/12/1993
Aircraft: CESSNA A188B, registration: N8677G
Injuries: 1 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.
DURING AERIAL APPLICATION ONE PROPELLER BLADE SEPARATED FROM THE ACFT. THE ACFT COLLIDED WITH A TREE DURING THE FORCED LANDING ROLL. EXAM OF THE PROPELLER REVEALED THAT A FATIGUE FRACTURE ORIGINATED AT A SCORE MARK IN THE HUB THREADS OF THE BLADE. DEPOSITS WERE FOUND IN THE FRACTURE ENRICHED BY CARBON & OXYGEN. GRAPHITE, THE LUBRICANT USED IN THE PROPELLER ASSEMBLY, IS CARBON BASED. TESTING SHOWED THAT THE BLADE'S HARDNESS & TENSILE STRENGTH WAS BELOW MFG SPECIFICATIONS. THE SAFETY BOARD BELIEVES THAT THE FRACTURE WAS OPENED UP DURING THE LAST PROPELLER OVERHAUL, ABOUT 583 OPERATING HOURS PRIOR TO THE ACCIDENT. ALSO, OIL REQUIRED IN THE HUB TO ALLOW EARLY DETECTION OF BLADE CRACKS WAS ABSENT.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: FATIGUE FAILURE OF THE PROPELLER BLADE WHICH RESULTED FROM IMPROPER OVERHAUL PROCEDURES, AND THE ABSENCE OF OIL IN THE PROPELLER HUB WHICH WOULD ALLOW THE DETECTION OF BLADE CRACKS.
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