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Originally Posted by Global Security
On 02 November 2007 an F-15C mishap resulted in the loss of the aircraft. The Accident Investigation Board found defects which indicated potential structural damage in the rest of the fleet. A failure of the upper right longeron, a critical support structure in the F-15C Eagle, caused the crash of a Missouri Air National Guard F-15C, four miles south-southeast of Boss, Missouri. The initial findings of the Accident Investigation Board, while at the mishap site Nov. 27, indicate the fleet of F-15s A-D might not be airworthy after a metallurgical analysis of the mishap aircraft. The findings focus specifically on the upper longerons, major structural components of the aircraft, which are located near the canopy of the aircraft and run along the side of the aircraft lengthwise.
The discovery of more structural damage in the F-15s prompted a 03 December 2007 stand-down order from Air Combat Command Commander Gen. John Corley. The stand-down does not impact the operational status of the F-15 E Strike Eagle. Maintainers performed methodical and time-intensive inspections on all F-15 Eagle A, B, C and D model aircraft, which revealed more cracks in the aircraft longerons. Maintainers at Langley initially found no cracks or evidence of fatigue in F-15 longerons; however, throughout the Air Force, maintainers had found cracks in the upper longerons of eight F-15s (as of 10 December 2007). Four of these aircraft were assigned to the Air National Guard's 173rd Fighter Wing, Kingsley Field, Ore.; two were assigned to the 18th Wing, Kadena Air Base, Japan; another was assigned to the 325th Fighter Wing, Tyndall AFB, Fla.; and one assigned to the ANG 131st Fighter Wing, St. Louis, Mo.
Every aircraft underwent all previously published time compliance technical order inspections. However, the cleared aircraft did not immediately return to flight. Technical experts at Warner Robins Air Logistics Center, Ga., developed new inspection techniques based on findings in parts of the mishap aircraft. These inspections were performed as soon as the new TCTO [time compliance technical order] was available for the affected F-15s. As part of the previous TCTO, maintenance crews around the Air Force stripped paint and performed non-destructive inspections in the F-15's upper longeron just aft of the canopies. Inspections are more than just a visual check. After the paint is stripped and bare metal is exposed, Airmen from the non-destructive inspection shop apply chemicals that reveal cracks under a black light. Other inspections in hard-to-see areas are done with a borescope - a tool that uses a tiny camera and fits in tight areas.
According to the Air Combat Command Accident Investigation Board report [released 10 January 2008], a technical analysis of the recovered F-15C wreckage determined that the longeron didn't meet blueprint specifications. This defect led to a series of fatigue cracks in the right upper longeron. These cracks expanded under life cycle stress, causing the longeron to fail, which initiated a catastrophic failure of the remaining support structures and led to the aircraft breaking apart in flight. The one longeron, already not up to design specifications, cracked apart under the stress of a 7G turn, the colonel said. This led to the other longerons failing as well, which then caused the cockpit to separate from the rest of the fuselage. The pilot was able to eject, but suffered a broken arm when the canopy snapped off.
Air Combat Command officials cleared a portion of its F-15 A through D models to begin flying on 09 January 2008. As of that date, the Air Force had approved 60 percent of F-15 A through D models to return to service with no flight restrictions.
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01-22-2008, 06:32 PM
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