ASN Wikibase Occurrence # 23250
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| Date: | Thursday 3 November 2005 |
| Time: | 20:20 UTC |
| Type: |  Boeing Vertol 107-II (CH-46A) |
| Owner/operator: | Helifor Industries |
| Registration: | C-GHFT |
| MSN: | 402 |
| Year of manufacture: | 1963 |
| Engine model: | General Electric CT58-140-1 |
| Fatalities: | Fatalities: 2 / Occupants: 2 |
| Aircraft damage: | Destroyed |
| Category: | Accident |
| Location: | South Bentick Arm, BC -
 Canada
|
| Phase: | Initial climb |
| Nature: | External load operation |
| Departure airport: | |
| Investigating agency: | TSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The helicopter was seen to break apart in flight during logging operations near Bella Coola. The fuselage broke into 2 sections and fell from about 300 feet agl. Both pilots were fatally injured and the helicopter destroyed; there was a small post-crash fire.
Findings as to causes and contributing factors
1. The limit switches from the occurrence actuator did not meet the manufacturer's specification for switch arm travel. Since the switches cannot move in the vertical axis, it is likely that the greater arm travel distance prevented activation of the retract limit switch.
2. Failure of the retract limit switch to activate caused the end fitting adapter to be driven into the face of the torsion bar, imposing a tensile load on the jack screw nut of over 1300 pounds.
3. This high tensile load created a stress concentration within the 0.001-inch thread-root radius that was higher than the jack screw nut material endurance limit, which in turn caused the jack screw nut to fail.
4. The aft rotor blades became unstable following failure of the speed trim actuator jack screw nut. The aft rotor blades tilted forward into helicopter fuselage, causing an in-flight break-up.
Accident investigation:
 |
|
Sources:
TSB
Images:
(c) TSB
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 27-Sep-2008 01:00 | ASN archive | Added |
| 24-Dec-2008 12:10 | harro | Updated |
| 10-Jan-2011 07:23 | TB | Updated [Time, Aircraft type, Cn, Other fatalities, Location] |
| 10-Jan-2011 08:30 | TB | Updated [Nature, Source, Narrative] |
| 13-Dec-2021 17:55 | TB | Updated [Operator, Source] |
| 28-Sep-2023 17:39 | Anon. | Updated [[Operator, Source]] |
| 28-Sep-2023 17:41 | harro | Updated [[[Operator, Source]]] |
Corrections or additions? ... Edit this accident description
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