ASN Wikibase Occurrence # 247567
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| Date: | Friday 5 February 2021 |
| Time: | 14:00 LT |
| Type: |  Hughes OH-6A Cayuse |
| Owner/operator: | U.S. Department of Agriculture APHIS |
| Registration: | N6639R |
| MSN: | 66-078784 |
| Total airframe hrs: | 14627 hours |
| Engine model: | Alison 250-C20B |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | between Horseshoe Bend and Gardena, Boise County, ID -
 United States of America
|
| Phase: | En route |
| Nature: | Unknown |
| Departure airport: | Nampa-KMAN, ID (MAN/KMAN) |
| Caldwell Industrial Airport, ID (KEUL) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
While conducting wildlife damage management operations at low altitude over hilly terrain, the pilot of the helicopter noted a loss of main rotor rpm. To regain main rotor rpm, he reduced the engine power demand by descending into a draw; however, the helicopter impacted terrain, rolled over, and came to rest on its left side. Two days before the accident flight, the pilot experienced a similar loss of main rotor rpm; however, he was able to safely land the helicopter. The pilot was unable to replicate the loss of main rotor rpm and continued the flight. The pilot believed that the event was an isolated anomaly and did not notify maintenance personnel.
Postaccident examination of the helicopter revealed an air leak located in the fuel cell outlet valve near the firewall. Subsequent examination of the fuel cell outlet valve revealed circumferential scratch marks around the barrel of the pipe. Damage due to cross-threading was observed on the first two threads. When the O-ring was removed, metal chips were located embedded throughout the O-ring. A review of the maintenance records indicated that the fuel system components were inspected during the 100-hour inspection, along with correspondence from the maintenance facility that a vacuum check of the fuel system was conducted during that inspection, with no anomalies noted. No entries were found in the maintenance records of any work done to the fuel outlet valve. The approved maintenance manual for the helicopter contained multiple warnings that air in the fuel system will cause a power reduction or flame out. It could not be determined when, or how, the fuel cell outlet valve developed a leak.
Probable Cause: A partial loss of engine power due to a leak in the fuel cell outlet valve.
Accident investigation:
 |
|
Sources:
NTSB WPR21LA107
FAA register: https://registry.faa.gov/aircraftinquiry/Search/NNumberResult?nNumberTxt=6639R
https://flightaware.com/live/flight/N6639R
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 07-Feb-2021 00:56 | Captain Adam | Added |
| 07-Feb-2021 01:35 | Geno | Updated [Time, Location, Source] |
| 09-Feb-2021 02:59 | Geno | Updated [Time, Aircraft type, Registration, Cn, Phase, Nature, Departure airport, Source, Narrative] |
| 11-Feb-2021 08:26 | RobertMB | Updated [Aircraft type, Cn, Source, Narrative] |
| 11-Feb-2021 12:34 | Aerossurance | Updated [Operator, Location, Nature, Source, Narrative] |
| 26-Sep-2022 19:03 | ASN Update Bot | Updated [Time, Cn, Operator, Other fatalities, Nature, Departure airport, Destination airport, Source, Narrative, Category, Accident report] |
| 26-Sep-2022 19:11 | harro | Updated [Operator, Source, Narrative] |
| 12-Nov-2022 02:15 | Ron Averes | Updated [Operator] |
Corrections or additions? ... Edit this accident description
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