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Cracks: The culprit in the Nov. 2 F-15 crash was a crack in a longeron behind and to the right of the pilot. The longeron was supposed to have a design life of 31,000 hours, which is longer than the anticipated life of the airplane. The part was improperly made, having a thickness in some areas that was too thin by several thousandths of an inch, and years of fatigue stress have caused it to crack. Cracks similar to that on the mishap aircraft have been found on nine other F-15s, but there is no rhyme or reason to them—they did not come from a particular lot, batch of materials, and affect aircraft made from 1978 to 1985. Accident Investigation Board director Col. William Wignall said the pattern is “random.” That, however, poses a dark question—what other bad parts might be lurking in the fleet? The Air Force expected to begin retiring some F-15s in the mid-1990s. Air Combat Command chief Gen. John Corley, observing the fact that his Eagles are long past retirement age, said, “100 percent of my fleet is fatigued.” (AIB executive board summary; see The Document File for multiple-volume AIB report)