ASN Wikibase Occurrence # 188621
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| Date: | Monday 11 July 2016 |
| Time: | 11:23 LT |
| Type: |  Bell 407 |
| Owner/operator: | Tennessee Valley Authority (TVA) |
| Registration: | N427TV |
| MSN: | 54106 |
| Year of manufacture: | 2012 |
| Total airframe hrs: | 1390 hours |
| Engine model: | Rolls Royce 250-C47B |
| Fatalities: | Fatalities: 1 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Folsomdale, N of Hickory, Graves County, KY -
 United States of America
|
| Phase: | Landing |
| Nature: | Executive |
| Departure airport: | Clarksville, TN (CKV) |
| Hickory, KY | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
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:
 |
|
Sources:
NTSB
http://aerossurance.com/helicopters/b407-maintenance-hf/
Location
Media:
KFVS12 News & Weather Cape Girardeau, Carbondale, Poplar Bluff
#OTD in 2016: critical flying control component was unnecessarily removed during an inspection say the #NTSB and when refitted, the fasteners were not lock-wired with fatal consequences. https://t.co/w90fNikuj8 #airworthiness #maintenance #accident #flightsafety #aviationsafety pic.twitter.com/71s76kXQ3I
— Aerossurance (@Aerossurance) July 11, 2020
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 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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