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ASN Wikibase Occurrence # 150932
Last updated: 26 April 2019
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Type:Silhouette image of generic B222 model; specific model in this crash may look slightly different
Bell 222UT
Owner/operator:Lifelink III
Registration: N225LL
C/n / msn: 47539
Fatalities:Fatalities: 0 / Occupants: 2
Other fatalities:0
Aircraft damage: Substantial
Location:St Paul, MN -   United States of America
Phase: En route
Departure airport:St. Paul, MN (PVT)
Destination airport:
Investigating agency: NTSB
During cruise flight the pilot lost control of the helicopter and an uncontrolled forced landing was made onto the top of a two-story industrial warehouse. The pylon mounted actuator support assembly had separated from the transmission case. The support assembly, attachment hardware, and portions of the transmission case were sent to the NTSB Materials Laboratory for analysis. According to the NTSB Materials Laboratory Factual Report, "... all of the studs showed progressive fatigue cracking from multiple origins." The report stated, "All but one stud fracture ... showed progression from diametrically opposed sides, typical of reversed bending fatigue loads." The report stated that all of the stud and dowel holes in the actuator support were, "... elongated on opposite sides from contact with the respective dowel or stud." The report further stated, "In addition to the elongation of the holes, the faying surfaces of the support and the transmission case were severely worn from relative movement. The directions of indicated movements and wear correspond to the axis of elongation of the respective support holes." The lead mechanic for the helicopter reported that one of the dowel pins was found during routine maintenance approximately one year prior to the accident date and the maintenance staff did not determine the identify the source of the dowel pin.
Probable Cause: The loss of clamp-up force between the transmission case and the pylon mounted actuator support assembly which resulted in fatigue failure of the threaded studs and dowel pins, the failure of the flight control system, helicopter control not being possible after the flight control failure, and the inadequate maintenance procedures by the company maintenance personnel.



Revision history:

30-Nov-2012 03:10 TB Added
21-Dec-2016 19:28 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
12-Dec-2017 18:33 ASN Update Bot Updated [Operator, Departure airport, Destination airport, Source, Narrative]

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