NTSB Identification: ANC92FA164.
The docket is stored on NTSB microfiche number 46803.
Nonscheduled 14 CFR
Accident occurred Friday, September 11, 1992 in EAGLE, AK
Probable Cause Approval Date: 09/17/1993
Aircraft: MCDONNELL DOUGLAS 369D, registration: N1096X
Injuries: 3 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.
SHORTLY AFTER TAKEOFF THE PILOT RADIOED HE WAS RETURNING DUE TO POOR VISUAL FLIGHT CONDITIONS, AND WAS LAST SEEN CIRCLING THE EAGLE RUNWAY. THE WRECKAGE WAS FOUND APRX 7 HRS LATER 150 YDS NORTH OF THE RUNWAY. THE BLUE M/R BLADE WAS FOUND SEPARATED; THE TRAILING ATTACHMENT LUGS OF BOTH THE UPPER AND LOWER BLADE ROOT FITTINGS WERE FRACTURED THROUGH THE HOLES, AND THE LEAD LAG DAMPENER LUG WAS ALSO FRACTURED. METALLURGICAL EXAMINATION REVEALED FATIGUE PROGRESSION ON ALL FOUR ROOT FRACTURES. OPERATOR MAINTENANCE PERSONNEL STATED THAT THEY WERE NOT AWARE OF AD91-17-04 REQUIREMENT TO REMOVE & INSPECT THE M/R BLADES AT 100-HR INTERVALS.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: AN INFLIGHT FATIGUE FAILURE AND SEPARATION OF A MAIN ROTOR BLADE, INADEQUATE OPERATOR MAINTENANCE AND INSPECTION, AND MATERIAL DEFECT.
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