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ASN Wikibase Occurrence # 41006
Last updated: 1 August 2020
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Date:05-NOV-1996
Time:14:00
Type:Silhouette image of generic UH1 model; specific model in this crash may look slightly different
Garlick TH-1L (Bell 204)
Owner/operator:private
Registration: N465JR
C/n / msn: 6423
Fatalities:Fatalities: 1 / Occupants: 1
Other fatalities:0
Aircraft damage: Written off (damaged beyond repair)
Category:Accident
Location:Leavenworth, WA -   United States of America
Phase: Unknown
Nature:External load operation
Departure airport:
Destination airport:
Investigating agency: NTSB
Narrative:
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. CAUSE: 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.

Sources:

http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20001208X07115&key=1


Revision history:

Date/timeContributorUpdates
24-Oct-2008 10:30 ASN archive Added
29-Jun-2014 17:50 TB Updated [Aircraft type, Cn, Nature, Source]
29-Jun-2014 18:03 TB Updated [Aircraft type]
21-Dec-2016 19:23 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]

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