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ASN Wikibase Occurrence # 30812
Last updated: 4 February 2020
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Date:14-DEC-1998
Time:11:00 PST
Type:Silhouette image of generic UH1 model; specific model in this crash may look slightly different
Bell UH-1H
Owner/operator:Northwest Helicopters
Registration: N94NW
C/n / msn: 5584
Fatalities:Fatalities: 0 / Occupants: 1
Other fatalities:0
Aircraft damage: Written off (damaged beyond repair)
Category:Accident
Location:Darrington, Washington -   United States of America
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Nature:Cargo
Departure airport:Darrington, Washington
Destination airport:Darrington, Washington
Investigating agency: NTSB
Narrative:
While in a hover during heavy-lift aero-logging operations, the vertical fin separated from the tail boom, resulting in an uncontrolled descent into the terrain. During the investigation, the NTSB Materials Laboratory determined that the separation was due to the propagation of a number of fatigue cracks which had initiated within the fourth rivet hole above where the left side of the spar fin cap protruded from the tail boom.

Although the FAA had previously issued Airworthiness Directive (AD) 97-20-09 to address the separation of vertical fins from UH-1 helicopters used in repeated heavy-lift operations, the Rotorcraft Directorate determined that the AD was not adequate. As a result, the Directorate initiated the formulation of a Priority Letter Airworthiness Directive requiring the replacement
of the original fin spar with one that '...has been shown to account for the effects of repeated heavy-lift operations.'

Sources:

http://dms.ntsb.gov/aviation/AccidentReports/t2k34lmwim5h0355g0wely451/E01292012120000.pdf


Revision history:

Date/timeContributorUpdates
27-Sep-2008 01:00 ASN archive Added
29-Jan-2012 19:26 Dr. John Smith Updated [Time, Total fatalities, Total occupants, Other fatalities, Location, Country, Phase, Nature, Departure airport, Destination airport, Source, Damage, Narrative]

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