Longeron Still Issue in F-15 Fleet

The Air Force grounded 83 of its two-seat F-16Ds late last month due to cracks in the aircraft’s canopy sill longeron, an issue that also has plagued the F-15 fleet for years. Laura McGowan, a spokeswoman for the 88th Air Base Wing, told Air Force Magazine the F-15 longerons and the associated back up structure continue to be a “hot spot” for the aircraft after three years of stress testing. The stress test puts years’ worth of strain and pressure on various parts of an example airframe in a compressed time period, to discover what parts of the structure are likely to fail in the future. “The primary findings from the test, thus far, have been known problem areas which are already inspected and repaired as part of the current depot maintenance package,” she said. These problem areas include the aft box of the wing and the longeron, which failed in 2007 causing an Air National Guard F-15C to break apart in mid-air. “Several new locations on the longeron have been identified as potential crack initiation sites, and as a result, the entire fleet has been inspected at these locations,” McGowan said. Recurrent inspections and repairs in the F-15 fleet are being developed and analyzed. “To date, no life limiting structural issues have been identified,” she added.