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ASN Wikibase Occurrence # 39234
Last updated: 3 December 2021
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Date:13-JUL-1996
Time:13:25
Type:Silhouette image of generic S64 model; specific model in this crash may look slightly different
Sikorsky CH-54A (S-64A)
Owner/operator:Silver Bay Logging
Registration: N541SB
MSN: 64-035
Fatalities:Fatalities: 1 / Occupants: 2
Other fatalities:0
Aircraft damage: Written off (damaged beyond repair)
Category:Accident
Location:16 mls NNE of Ketchikan, AK -   United States of America
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Nature:External load operation
Departure airport:Shelter Cove, AK
Destination airport:
Investigating agency: NTSB
Narrative:
The pilot & copilot were on an external load, aero logging operation in a military surplus helicopter, lifting an estimated load of 18,000 lbs. Ground personnel heard a popping sound, then saw the tailrotor begin to slow down as the helicopter began to yaw/spin. It descended to sloping terrain in an area of cut logs. Postcrash exam of the tailrotor drive shaft revealed a separation at the number 5 bearing position. The shaft separation exhibited evidence of high heat & melting of adjoining shaft surfaces. The bearing & its housing were not recovered. The bearing had accrued 505 hrs of service, & was 1 of 2 bearing model numbers that were in use. The bearing was manufactured in 1991, & was purchased by the operator from surplus military supplies. The supplier (of the bearing to the operator) had performed an exterior exam of the bearing & marked 'relubed 10/95' on the bearing box. Exam of the remaining tailrotor drive shaft bearings revealed evidence of low grease fill, water & glycol contamination, & wear patterns consistent with misalignment. In civilian service, the bearing was an 'on condition' part. The operator established a service life of 1,000 hours for aero logging operations. A shelf life for the bearing was not established. The manufacturer indicated the bearing should support a 5 year shelf life. Other operators of the accident helicopter in aero logging reported similar examples of low grease fill & bearing contamination from water in both available models of bearing. CAUSE: failure of the number 5 tailrotor bearing. A factor relating to the accident was: the uneven/steep sloping terrain, where the pilot was forced to land. Possible factors were: inadequate handling/labeling of the 'relubed' bearing by intermediate supplyier(s), and/or insufficient shelf life/service limits for military surplus parts.

Sources:

1. http://www3.ntsb.gov/aviationquery/brief.aspx?ev_id=20001208X06129&key=1
Ex CH-54A Tarhe 68-18433 US Army


Revision history:

Date/timeContributorUpdates
24-Oct-2008 10:30 ASN archive Added
24-Dec-2009 12:20 TB Updated [Cn, Operator, Other fatalities, Location, Source]
26-Dec-2009 07:33 TB Updated [Aircraft type]
19-Mar-2011 09:36 TB Updated [Time, Location, Source]
21-Dec-2016 19:23 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]

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