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ASN Wikibase Occurrence # 158020
Last updated: 17 August 2021
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Type:Silhouette image of generic B06 model; specific model in this crash may look slightly different
Bell 206B-3 JetRanger III
Registration: N90146
MSN: 1614
Fatalities:Fatalities: 0 / Occupants: 1
Aircraft damage: Substantial
Location:Near Gonzales, Chualar, CA -   United States of America
Phase: Landing
Departure airport:Chualar, CA
Destination airport:Chualar, CA
Investigating agency: NTSB
The pilot stated that he was operating the helicopter at a low altitude when he heard a loud boom and then noted a decrease in main rotor rpm. During the ensuing emergency landing, the helicopter impacted the ground, the tail boom separated from the fuselage, and the helicopter rolled onto its right side. Postaccident examination revealed that the main driveshaft had disconnected and that the bolts attaching the forward coupling to the transmission had failed. Portions of two of the four bolts that attached the forward coupling to the transmission were found, and the fractured threaded remnants (with nuts attached) were examined. One of the remnants was fractured through its entire cross-section due to fatigue, and the other remnant fractured through about 75% of its cross-section due to fatigue; the remainder of the failure on this remnant occurred in overload. Both fracture faces had multiple fatigue origins around about 1/4 of their circumferences, indicating relatively high stresses. No mechanical damage was noted at the fatigue origin locations. One of the remnants displayed smearing of adjacent threads and decreased height of the nut, suggesting this bolt had a relatively large amount of play. It is likely that the large amount of play was due to improper torqueing of the bolts when the driveshaft was reinstalled after extensive maintenance that was performed on the helicopter about 3 months and 197 flight hours before the accident.
Probable Cause: Maintenance personnel's failure to properly tighten the bolts securing the main driveshaft to the transmission, which resulted in fatigue failure of the bolts and disconnection of the driveshaft during low-altitude flight.



Accident investigation:
Investigating agency: NTSB
Status: Investigation completed
Download report: Final report

Revision history:

05-Aug-2013 21:35 Geno Added
08-Aug-2013 22:09 Geno Updated [Time, Aircraft type, Location, Departure airport, Destination airport, Source, Narrative]
21-Dec-2016 19:28 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
29-Nov-2017 08:58 ASN Update Bot Updated [Operator, Other fatalities, Departure airport, Destination airport, Source, Narrative]

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