NTSB Identification: SEA83FA009
14 CFR Part 133: Rotorcraft Ext. Load
Accident occurred Thursday, October 14, 1982 in CASCADE, ID
Probable Cause Approval Date: 10/14/1983
Aircraft: BOEING VERTOL 107, registration: N6676D
Injuries: 2 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.

DURING A LOG SLINGING OPERATION A LOUD BANG WAS HEARD & THE ACFT WAS OBSERVED TO RAPIDLY DESCEND VERTICALLY TO THE GROUND WITH NUMEROUS SMALL FRAGMENTS FALLING IN THE SAME VICINITY. THE #5 SYNCHRONIZATION SHAFT WAS FOUND TO BE FRACTURED AT THE FORWARD END ABOUT 9 INCHES AFT OF THE CONNECTION ASSY TO THE #4 SHAFT. THIS RESULTED IN AN OUT OF SYNCHRONIZATION CONDITION BETWEEN THE FORWARD & AFT ROTOR BLADES AS WELL AS A LOSS OF POWER TO THE FORWARD ROTOR. A FATIGUE FRACTURE ORIGINATED IN THE AFT MOST RING OF RIVET HOLES. THE FATIGUE CRACKS PROPOGATED FROM MULTIPLE ORIGINS WITHIN THOSE RIVET HOLES WHERE A "STEP" WAS FOUND AT THE BASE OF THE HOLE & CLOSEST TO THE INSIDE DIAMETER OF THE SHAFT.ALL RIVET HOLES IN THE FORWARD END OF THE SHAFT HAD TOPOGRAPHIC FEATURES SIMILAR TO THOSE PRODUCED IN A STEEL PLATE BY DELIBERATELY DRILLING HOLES WITHOUT COMPLETE PENETRATIONS.

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

ROTOR DRIVE SYSTEM,ENGINE TO TRANSMISSION DRIVE..IMPROPER

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

INADEQUATE QUALITY CONTROL..PRODUCTION/DESIGN PERSONNEL

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

ROTOR DRIVE SYSTEM,ENGINE TO TRANSMISSION DRIVE..FATIGUE

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

ROTOR DRIVE SYSTEM,ENGINE TO TRANSMISSION DRIVE..FAILURE,TOTAL

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

ROTOR DRIVE SYSTEM,ENGINE TO TRANSMISSION DRIVE..DISABLED

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