ASN Wikibase Occurrence # 157845
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| Date: | Saturday 27 July 2013 |
| Time: | 12:55 |
| Type: |  Robinson R44 Raven II |
| Owner/operator: | Rocky Mountain Rotors |
| Registration: | N25WH |
| MSN: | 10481 |
| Year of manufacture: | 2004 |
| Total airframe hrs: | 786 hours |
| Engine model: | Lycoming IO-540 SER |
| Fatalities: | Fatalities: 1 / Occupants: 3 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | 10 miles up Prospect Creek Road, near Thompson Falls, MT -
 United States of America
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | Survey |
| Departure airport: | Polson, MT (8S1) |
| Thompson Fall, MT | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The helicopter was flying northeast following a line of utility poles for the aerial survey flight. A surviving passenger, who occupied the left rear seat, reported that the helicopter began to rotate in a clockwise direction just before impact. A second surviving passenger, who occupied the left front seat, stated that the helicopter was flying straight and level before it began to spin. He added that, before impact, he heard the low rotor rpm warning horn. The helicopter impacted heavily forested terrain in a steep nose-down, right-bank attitude. At the time of the accident, the helicopter was about 200 lbs below its maximum gross weight. Wind was calculated to be between 2 and 16 knots from the southwest with maximum gusts of about 20 knots near the accident site, which would have resulted in a tailwind condition. Examination of the helicopter did not reveal any anomalies that would have precluded normal operation.
Video footage recorded by a passenger showed the helicopter traveling about 39 knots on a northeasterly heading and at an altitude of about 200 ft above ground level. The groundspeed then began to decay to about 30 knots over a period of about 30 seconds. The helicopter then yawed right, and the groundspeed dropped to 22.6 knots. The helicopter then appeared to develop an uncontrollable right spin, and the video ended with the helicopter crashing into the forest below. It is likely that the combination of the helicopter's high gross weight, the reduction in airspeed, and the tailwind condition led to a loss of tail rotor effectiveness, which resulted in the right yaw from which the pilot did not recover control.
Probable Cause: The pilot's failure to maintain helicopter control while operating in conditions conducive to a loss of tail rotor effectiveness.
Accident investigation:
 |
|
Sources:
NTSB
FAA register: http://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=N25WH
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 29-Jul-2013 02:15 | gerard57 | Added |
| 29-Jul-2013 19:29 | Geno | Updated [Aircraft type, Registration, Cn, Operator, Location, Phase, Nature, Source] |
| 21-Dec-2016 19:28 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 29-Nov-2017 08:48 | ASN Update Bot | Updated [Operator, Other fatalities, Departure airport, Destination airport, Source, Narrative] |
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