NTSB Identification: ANC07FA109.
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Accident occurred Sunday, September 30, 2007 in King Salmon, AK
Probable Cause Approval Date: 09/26/2008
Aircraft: Helio H-295, registration: N295BA
Injuries: 4 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The float-equipped airplane was transporting sport-fishing clients returning to a lodge from a remote fishing site. The pilot contacted lodge personnel while en route, and estimated his arrival time in about 3 minutes. When the airplane failed to arrive, an aerial search discovered the wreckage about 10 miles from the lodge, along the anticipated flight route. The NTSB's investigation revealed evidence that the airplane's lower left wing to fuselage attachment cap fitting had failed in flight, which resulted in the airplane's uncontrolled descent. The deformation at the upper forward and aft wing attachment points suggested that the airplane's left wing, in part, had failed in flight, but did not completely separate from the airplane. A subsequent metallurgical examination revealed that the fractured wing to fuselage attachment cap fitting displayed evidence of fatigue cracking, which emanated from areas of corrosion pitting. A Safety Board metallurgist noted that the corrosion pitting was located in the interior portion of the pin/bolt hole, where a large bore pin/bolt resides when the wing is attached to the fuselage, which is not visible when the bolt/pin is installed. The metallurgist also noted that there was corrosion on the forward and aft faces of the fitting that would have been visible. Other than the corrosion pitting on the attachment cap fittings and pins/bolts, no metallurgical anomalies were discovered. On September 9, 2008, the FAA issued a special airworthiness information bulletin (SAIB CE-08-47) recommending a visual inspection for evidence of corrosion, cracking, and other damage on the spar fittings, attachment bolts and related structure, to preclude a structural in-flight failure of the wings.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: A corrosion-induced fatigue fracture of the airplane's left wing to fuselage attachment cap fitting, which resulted in a partial separation of the left wing, and an uncontrolled descent. Full narrative available
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