WEEK 8
H2F brings you the ‘helicopter mayday of the week’ with a short accident report summary. I tell you what happened. You think more about why it happened. We all learn from it. Because that’s what accident reporting is for.
TITLE
Low-altitude ridge flight resulting in tree strike CFIT.
WHAT?
A Eurocopter AS-350-B3 operating under contract to the U.S. Forest Service was tasked with transporting a relief fire lookout and moving supplies using external cargo baskets attached to the skids. After dropping off personnel at a mountaintop lookout, the helicopter departed with three occupants and cargo. During the return flight over mountainous terrain, the helicopter struck a tree near a ridgeline, leading to loss of control, breakup, and a post-impact fire further down the slope.
WHERE?
Near Yellow Pine, Idaho, along a mountain ridge-line in steep, rugged forested terrain.
WHEN?
August 13, 2006, at approximately 17:10 local time. The NTSB final report was published on May 29, 2007.
HOW?
Evidence indicated the helicopter was flying at intentionally low altitude while maneuvering along terrain contours. The aircraft struck a tall dead conifer near the ridge crest. Debris distribution indicated a rotor strike and sudden stoppage event followed by uncontrolled descent. The wreckage path extended 2,000 feet downslope before the helicopter came to rest on a forest road, where it was consumed by fire. Investigators found no pre-impact mechanical anomalies.
CONDITIONS?
Mountainous terrain with narrow valleys and ridgelines, and multiple forest fires in the region reduced visibility in lower areas. The return leg was flown toward the late afternoon sun. Weather conditions were otherwise VMC with light winds, and the pilot was known by crew to frequently follow ridge-lines during navigation.
OUTCOME?
The helicopter was destroyed by impact forces and post-crash fire. The pilot and three passengers sustained fatal injuries. All major components were accounted for, and the investigation determined that the accident sequence began with a tree strike near the ridge-line.
WHY?
- Pilot’s intentional low-altitude flight and maneuvering near terrain.
- Failure to maintain adequate altitude..
- Mountainous terrain environment increasing manoeuvring risk.
- Possible low contrast light conditions and flight into sun reducing visibility.
REFERENCE?
National Transportation Safety Board. (2007, May 29). Aviation investigation final report: Accident number SEA06GA158 (Eurocopter AS-350-B3, N355EV). National Transportation Safety Board. https://data.ntsb.gov/Docket?ProjectID=64316
https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/64316/pdf
https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/66303/pdf
Note:
Accident reports selected from the following open source databases: US NTSB; UK AAIB; Flight Safety Foundation’s Aviation Safety Network; Australia’s ATSB. Ireland’s AAIU; Taiwan’s TTSB; France’s BEA; Spain’s CIAIAC. Germany’s BFU.
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