ASN Wikibase Occurrence # 23446
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| Date: | Thursday 30 October 1997 |
| Time: | 16:15 LT |
| Type: |  Boeing Vertol BV234UT Chinook (CH-47) |
| Owner/operator: | Columbia Helicopters |
| Registration: | C-FHFH |
| MSN: | MJ001 |
| Year of manufacture: | 1981 |
| Fatalities: | Fatalities: 2 / Occupants: 2 |
| Aircraft damage: | Destroyed |
| Category: | Accident |
| Location: | Comox Lake, BC -
 Canada
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | External load operation |
| Departure airport: | |
| Investigating agency: | TSB |
| Confidence Rating: |  Information is only available from news, social media or unofficial sources |
The Boeing Vertol BV-234 helicopter with two pilots on board, was engaged in heli-logging operations in the Comox Lake area on Vancouver Island, British Columbia. At 1615 Pacific standard time, ground personnel attached a log, estimated to have weighed 16 000 pounds, to the hook at the end of the 250-foot long-line suspended below the helicopter. The helicopter had lifted the log two-thirds of the way off the steep terrain, with one end still in contact with the ground, when it commenced a rapid right turn. In the next 5 to 10 seconds, the helicopter continued to turn rapidly to the right several times, travelled laterally, then descended in a nearly-level attitude and struck the ground. The helicopter broke up at impact and the two pilots suffered fatal injuries; there was a limited post-accident fire.
Findings as to Causes and Contributing Factors
The U12 analog switch installed in the yaw axis of the No.2 AFCS computer failed in electrical overload, and sent an instantaneous extension signal to the No.2 yaw ELA.
The rapid ELA extension in the yaw flight control system almost certainly caused the yaw LBA to burst and broke the yaw connecting link, preventing the pilot from countering a right-yaw condition.
Without yaw control, the pilots likely became disoriented and could not prevent the helicopter from striking the terrain.
Findings as to Risk
The practice of not using shoulder harnesses during vertical reference flying exposes pilots to greater risk of ineffective restraint during an in-flight emergency.
Other Findings
No indication was found of any malfunction or pre-existing mechanical defect with the engines or related systems that could have contributed to the accident.
The only pre-impact anomalies identified with the helicopter during the investigation were the U12 analog switch in the yaw axis of the flight control system, the burst yaw LBA, and the fractured yaw connecting link. No other systems revealed pre-impact failures.
Accident investigation:
 |
|
Sources:
http://www.tsb.gc.ca/eng/rapports-reports/aviation/1997/a97p0303/a97p0303.asp
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 27-Sep-2008 01:00 | ASN archive | Added |
| 02-Jan-2010 07:38 | TB | Updated [Aircraft type, Other fatalities, Location, Source] |
| 21-Jan-2016 20:37 | Aerossurance | Updated [Time, Aircraft type, Source, Narrative] |
| 21-Jan-2016 20:40 | Aerossurance | Updated [Aircraft type] |
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