NTSB Identification: ANC05IA016.
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Nonscheduled 14 CFR (D.B.A. Nippon Cargo Airlines)
Incident occurred Sunday, December 05, 2004 in Anchorage, AK
Probable Cause Approval Date: 02/28/2006
Aircraft: Boeing 747SR-146B SF, registration: JA8158
Injuries: 3 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
The 14 CFR Part 129 non-scheduled international cargo flight had a rapid decompression at 30,000 feet msl, and returned to the takeoff airport. An examination revealed an elliptical tear in the right side of the pressure bulkhead web separating the electronics service bay from the nose wheel well. The tear extended about 12-inches along a horizontal rivet line, with both ends of the torn skin turned downward approximately 80-90 degrees. The damaged area (STA 260-280, WL 160-170) was excised from the structure, and an examination of the fracture mechanism was conducted. The fracture examination disclosed that the web fracture was initiated by fatigue from multiple origins on the outboard web surface within the pressure vessel. Ten separate fatigue cracks propagated through the full web thickness before the onset of rapid ductile tearing. Each fatigue crack formed adjacent to a fastener hole common with the WL 170 beam, and was in line with the edge of the bonded strip doublers on the inboard surface (wheel well side). The web material met all the engineering specifications. At the time of the incident, the airplane had logged 58,185 flight hours, and 27,243 cycles/landings. Inspection criteria for the affected area is contained in a manufacturer's Service Bulletin and their Alert Revisions 1 thru 4. Following the examination of the incident airplane, Alert Revision 4 was amended to specify more frequent inspections of the affected area.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The fatigue and subsequent fracture of a portion of the airplane's pressure bulkhead, which resulted in a rapid decompression during cruise flight. Full narrative available
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