NTSB Identification: SEA97LA025.
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Accident occurred Tuesday, November 05, 1996 in LEAVENWORTH, WA
Probable Cause Approval Date: 08/14/2001
Aircraft: Garlick TH-1L, registration: N465JR
Injuries: 1 Fatal.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The pilot/operator, who had been utilizing the rotorcraft for heavy log lifting operations for the previous 18 months, was initiating a log lift cycle from a hover when the vertical stabilizer separated from the restricted category Garlick TH-1L. The rotorcraft subsequently descended out of control, impacting wooded, sloped terrain. Post-crash metallurgical examination discovered fatigue fractures emanating from a rivet hole within all five layers of the left side aluminum spar cap buildup for the vertical stabilizer. Additionally, fatigue cracking was observed within the tail boom skin near the vertical stabilizer and additional rivets were noted in both sides of the tail boom skin area. The tail boom skin crack was noted to have two separate stop holes drilled in its progression. Maintenance records showed no evidence of an inspection of the spar cap area or internal inspection of the tail cone or vertical fin at the time of installation of six blind rivets in the vertical fin, 18 months previous to the accident. No record was found recording the time of stop-drilling the skin crack progression. Examination of the riveted structure in the vicinity of the tailboom-to-vertical stabilizer junction revealed 30 blind rivets without paint on their exterior or interior ends on the left side of the vertical stabilizer, including seven that were directly adjacent to the separation point in the left cap of the stabilizer front spar. Four similar rivets were noted on the right side of the vertical stabilizer. Helicopter logging operations require repetitive high-stress/high-cycle operations.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: Fatigue failure of the vertical stabilizer spar cap and subsequent loss of the rotorcraft's vertical stabilizer. Factors include inadequate inspection or trouble-shooting of the aircraft tail cone and vertical stabilizer at and after the time sheet-metal skins were stop-drilled and rivets were replaced, and repetitive cycles associated with helicopter logging operations. Full narrative available
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