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ASN Wikibase Occurrence # 188621
Last updated: 23 September 2021
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Time:11:23 LT
Type:Silhouette image of generic B407 model; specific model in this crash may look slightly different
Bell 407
Owner/operator:Tennessee Valley Authority (TVA)
Registration: N427TV
MSN: 54106
Fatalities:Fatalities: 1 / Occupants: 1
Aircraft damage: Substantial
Location:Folsomdale, N of Hickory, Graves County, KY -   United States of America
Phase: Landing
Departure airport:Clarksville, TN (CKV)
Destination airport:Hickory, KY (NONE)
Investigating agency: NTSB
The pilot was performing a visual approach to a landing zone to board an additional crewmember. A witness reported that there were no abnormalities in the helicopter's sound or position, until it was approximately 75 to 100 feet above the ground. Suddenly, the main rotor tilted to the right. Immediately after, the entire helicopter banked to its right and fell to the ground on its right side, where it came to rest. The main rotor blades broke apart during the impact sequence. The engine continued to run after the accident, and was subsequently shut down by responding personnel.

An examination of the wreckage revealed that the collective lever, located at the front and bottom of the swashplate support, was disconnected from the pivot sleeve. The collective lever was designed to move the pivot sleeve vertically on the swashplate support, via direct linkage from the cockpit collective control, to change the pitch on all the main rotor blades simultaneously. The collective lever pins and screws that attached the collective lever to the pivot sleeve were missing; they were later found loose, near the main rotor area. The safety wires intended to secure the screws to the pins were missing. Examination of the hardware at the NTSB Materials Laboratory revealed that the safety wires not present, and the screws backed out over time, resulting in the complete loss of collective control in flight.

Maintenance on the helicopter was performed about 38 flight hours prior to the accident. The maintenance included a 24-month inspection that required examination of the flight control bolts and nuts. The collective lever pins were not specifically included in that inspection. Two mechanics and a maintenance foreman, all employees of the operator, performed the maintenance, and all reported during postaccident interviews that they did not recall removing the safety wire or examining the pins. However, the foreman added, "I could see why it [examination of the collective lever pins] could have been done. The 24-month flight control bolt inspection was being performed, why not pull them and look at them too. I've done it before." Two of the mechanics reported that they would occasionally be "pulled off" one aircraft to work on another, and there was no work interruption policy in place. Thus, given that the safety wires were missing, it is likely that they were removed and not replaced during the most recent maintenance and that maintenance personnel did not recall taking that action due to possible work interruptions.

Subsequent to the accident, the operator implemented numerous safety initiatives to prevent recurrence, including two independent safety audits, a formal fatigue risk management program, a Safety Management System, a formal tool/material accountability program, new work interruption policies, creation of a formally-trained Safety Officer position, and a formal process for the communication of safety-critical information.

Probable Cause: Company maintenance personnel's inappropriate removal without replacement of the safety wires on the collective lever pin screws during a recent maintenance inspection, which resulted in the screws backing out and led to a loss of collective control in flight.



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


KFVS12 News & Weather Cape Girardeau, Carbondale, Poplar Bluff

Revision history:

12-Jul-2016 06:51 gerard57 Added
12-Jul-2016 12:44 CTYONE Updated [Time, Aircraft type, Operator]
12-Jul-2016 16:52 Anon. Updated [Location]
12-Jul-2016 16:53 harro Updated [Registration, Cn, Operator, Location, Source]
12-Jul-2016 20:59 Geno Updated [Location, Phase, Nature, Destination airport, Source, Narrative]
13-Jul-2016 19:26 harro Updated [Embed code, Narrative]
22-Jul-2016 07:36 Aerossurance Updated [Time, Location, Departure airport, Source, Narrative]
21-Jul-2017 13:19 Aerossurance Updated [Narrative]
23-Jul-2017 18:53 Aerossurance Updated [Narrative]
24-Jul-2017 07:44 Aerossurance Updated [Source]
19-Aug-2017 16:44 ASN Update Bot Updated [Time, Operator, Other fatalities, Nature, Departure airport, Destination airport, Source, Embed code, Damage, Narrative]
11-Jul-2020 09:40 Aerossurance Updated [Time, Operator, Location, Source, Embed code]

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