ASN Wikibase Occurrence # 155589
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| Date: | Thursday 25 April 2013 |
| Time: | 10:16 |
| Type: |  Bell 407 |
| Owner/operator: | Flathead Co Sheriff's Office |
| Registration: | N937GR |
| MSN: | 53282 |
| Year of manufacture: | 1998 |
| Total airframe hrs: | 1308 hours |
| Engine model: | Allison 250-C47B |
| Fatalities: | Fatalities: 0 / Occupants: 3 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Mount Aenaes, Jewel Basin, MT -
 United States of America
|
| Phase: | Landing |
| Nature: | Unknown |
| Departure airport: | Kalispell, MT (S27) |
| Kalispell, MT (S27) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The pilot reported that, while conducting a reconnaissance orbit over mountainous terrain, he crossed over a ridgeline and then lost directional control of the helicopter. He applied full left pedal and lowered the nose and collective in an attempt to regain control. The helicopter subsequently impacted the uneven snow-covered terrain and rolled onto its right side.
Postaccident examination of the airframe and engine revealed no evidence of mechanical malfunction or failures that would have precluded normal operation. A weather study for the area around the accident site revealed that the temperature profile and windy environment supported strong up/downdrafts with the potential for mountain wave formation near the altitude at which the flight was maneuvering. It is likely that the pilot was unable to maintain control of the helicopter as a result of a loss of tail rotor effectiveness while operating in the high-altitude environment and in an area with strong up/downdrafts and possible mountain wave activity.
Probable Cause: The pilot’s failure to maintain helicopter control while maneuvering over mountainous terrain in strong up/downdrafts and possible mountain wave activity, which resulted in a loss of tail rotor effectiveness.
Accident investigation:
 |
|
Sources:
NTSB
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 26-Apr-2013 02:56 | gerard57 | Added |
| 26-Apr-2013 10:53 | krasatpi | Updated [Cn] |
| 26-Apr-2013 18:31 | Geno | Updated [Time, Operator, Location, Nature, Source, Narrative] |
| 21-Dec-2016 19:28 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 28-Nov-2017 14:32 | ASN Update Bot | Updated [Operator, Total occupants, Other fatalities, Nature, Departure airport, Destination airport, Source, Narrative] |
| 30-May-2023 07:39 | Ron Averes | Updated [[Operator, Total occupants, Other fatalities, Nature, Departure airport, Destination airport, Source, Narrative]] |
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