November 30, 200718 yr From Flight International DATE: 30/11/07 SOURCE: Flightglobal.com USAF: F-15s risk catastrophic design weakness By Stephen Trimble The US Air Force Boeing F15A-D Eagle fleet is grounded after preliminary findings of a crash investigation show signs of a design weakness. Air Combat Command (ACC) ordered the stand-down until the airframes can be inspected. An inspection checklist is being prepared by the Warner-Robins Air Logistics Center, an ACC spokesman says. An ongoing investigation of a 2 November crash is focusing on potential failure of the F-15’s upper longerons near the canopy seal. Recent inspections found cracks in this same area on two other F-15Cs. A Boeing simulation analysis shows such cracks could lead to “catastrophic failure”, the air force says. The second grounding comes a week after the full F-15 fleet returned to flight. The initial order to ground the fleet came immediately after the 2 November crash, in which the aircraft partially disintegrated in mid-air during a routine training flight above Missouri.
December 6, 200718 yr Author From Flight International DATE: 05/12/07 SOURCE: Flightglobal.com USAF F-15s remain grounded as more cracks found By Graham Warwick US Air Force Boeing F-15A-Ds are to remain grounded, even after structural inspections are completed, until investigation of the November crash is complete and a solution to fuselage longeron cracking is developed. The F-15s had been returning to flight after undergoing inspections, called time compliance technical orders (TCTO), but on 3 December the head of USAF Air Combat Command, Gen John Corley, ordered the aircraft to remain grounded. ACC says the decision followed a briefing on the investigation into the 2 November crash of a Missouri Air National Guard F-15C following structural failure, in which investigators reported they had found additional longeron cracking in the mishap aircraft. Since ordering inspection of all F-15A-Ds, the USAF has found longeron cracks in two aircraft operated by the Oregon Air National Guard. Both were built in the early 1980s, and are about the same age as the Missouri mishap aircraft, says ACC. Additional TCTOs were ordered on 29 November and so far more than 195 of the USAF’s 445 F-15A-Ds have undergone these inspections, says the command. “The TCTOs are still out there, and aircraft will still undergo inspection, but even if they pass they will not fly,” says ACC. The command does not know whether the solution to the cracking problem will be “a repair, more TCTOs or what, and we are not putting a date to it.” Grounding of the F-15s continues to be used by US Air Force leadership to underline its need for additional funding to continue procurement of the Lockheed Martin F-22A beyond the planned 183 aircraft.
February 20, 200818 yr Author From Flight International DATE: 20/02/08 SOURCE: Flightglobal.com US Air Force clears remaining Boeing F-15s to fly By Graham Warwick All remaining US Air Force Boeing F-15A-D Eagles have been returned to flight, contingent on completion of individual inspections on each aircraft's fuselage longerons. The USAF does not expect any of the 149 aircraft to require repair and says there will be no operating restrictions on Eagles that pass these final inspections. But all F-15A-Ds will require repetitive checks for longeron cracks every 400 flying hours. After a lengthy series of grounding and inspections following the 2 November 2007 crash of a Missouri Air National Guard F-15C, caused by structural failure, longeron cracks have been found in only nine of the US Air Force's 438 A- to D-model Eagles. The fatigue cracks were found where machining during manufacture had reduced the thickness of the upper fuselage longerons below blueprint specification or where there was surface roughness that could cause stress concentration. On 8 January, the USAF returned 259 of the F-15s to flight after they passed inspections for manufacturing deficiencies. The remainder remained grounded because at least one longeron on each aircraft did not meet blueprint specification at one or more points. The F-15s that remained grounded are undergoing tailored inspections unique to each tail number. The USAF has recommended that aircraft with longerons that do not meet specification, but pass these inspections, be returned to flight, effectively ending the groundings. Air Combat Command says it has not been decided whether the nine aircraft with longeron cracks will be repaired, although the Warner Robins Air Logistics Center responsible for F-15 depot overhaul is manufacturing a batch of replacement longerons.
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