ASN Wikibase Occurrence # 4870
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| Date: | Saturday 17 July 1976 |
| Time: | 18:04 |
| Type: |  Bell 47G-3B1 |
| Owner/operator: | Shasta Helicopter |
| Registration: | N7901S |
| MSN: | 6576 |
| Fatalities: | Fatalities: 2 / Occupants: 2 |
| Aircraft damage: | Destroyed |
| Category: | Accident |
| Location: | Petersburg, AK -
 United States of America
|
| Phase: | Take off |
| Nature: | Private |
| Departure airport: | Big John Bay Camp, AK |
| Petersburg, AK | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Information verified through data from accident investigation authorities |
The helicopter was used to move fire crews to remote work sites in the morning and returned them in the afternoon to the Rowan Bay Camp.
At about 17:15 hours Alaska Daylight Time, the helicopter departed from the Rowan Bay Camp headed for the Big John Bay Camp with a final destination of Petersburg. A Forest Service employee was on board, desiring to go to Petersburg on his day off. At about 17:30 ADT, the helicopter landed at the Big John Bay Camp, the pilot loaded two empty propane bottles onto the external racks, and secured the bottles with a bungee cord. At about 17:50 ADT, the helicopter again took off with one passenger enroute to Petersburg. At a point five miles from Petersburg in Duncan Pass, the helicopter crashed.
The helicopter was not missed until Monday, July 19th, when it could not be located for work. A search was then initiated and the wreckage was located.
Upon investigation of the wreckage, it was determined that initial impact into a large snag occurred about 25 feet above the ground. However, there was lack of tree and branch breakage near the major wreckage.
The helicopter was believed to be on a true course of 095 degrees at the point of impact. After contacting the snag, the helicopter slid down it, scarring it heavily, and came to rest inverted at its base. A fire erupted, burning the cockpit and engine areas. The main rotor mast was broken and the main rotor was separated from the helicopter. The broken piece of mast was not found. The tail rotor blades were separated from the gearbox and the tail rotor gearbox was separated from the helicopter. The tail rotor blade was found 411 feet from the fuselage of the helicopter.
The tail rotor blade had a mandatory change time of 600 hours. At the time of the mishap, the blades had been installed on this helicopter for a total of 622 hours.
Weather at the time of the mishap was estimated at 1,500 feet overcast, better than five miles visibility, and gusty winds to 20 knots from the south. There were rain showers of varying intensity in the area.
Further analysis of tail rotor blade Serial #A-376016 A-376008, which had been found 411 feet from the
fuselage of the helicopter, revealed that this blade had a separation fracture at the grip area. Initial National Transportation Safety Board (NTSB) reports indicated that the separation was caused by fatigue failure of the tail rotor blade material. This caused severe vibration, separating the tail rotor gearbox and remaining blade from the helicopter. This then caused the loss of control of the helicopter, which resulted in the mishap.
The pilot and passenger died instantly of injuries sustained in the mishap.
Accident investigation:
|
Sources:
NTSB
https://www.researchgate.net/publication/2840945_United_States_Department_of_Agriculture_Forest_Service
History of this aircraft
Other occurrences involving this aircraft
| 15 January 1998 | N7901S | Desert Eagle Helicopters Inc. | 0 | Magdalena, NM | |
sub |
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 25-Feb-2008 12:00 | ASN archive | Added |
Corrections or additions? ... Edit this accident description
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