The US Air Force has detected a possibly "catastrophic" design weakness in the Boeing F-15A-D. Air Combat Command on 28 November grounded all F-15s excluding the F-15E Strike Eagle.
Preliminary findings from an investigation of an accident on 2 November - in which an F-15C disintegrated in mid-air - revealed cracks in the F-15's upper longerons near the canopy seal.
Moreover, recent inspections found cracks in the same area on two other F-15s. According to the USAF, simulations by Boeing indicate such cracks could cause "catastrophic failure".
The order to ground the jets came one week after the full fleet returned to flight. The 2 November crash prompted a round of inspections, but the longeron cracking issue was not detected from a metallurgical analysis of the wreckage until 27 November.
Warner-Robins Air Logistics Center, which is responsible for sustaining the F-15s, was preparing an inspection checklist late last week, the ACC says.
The grounding order for each jet will remain in effect until the longerons in their forward fuselages are inspected for cracks.
The severity of the cracking problem will not be clear until the inspections are complete, but the USAF may face the need to fund a structural redesign of the forward fuselage.
The grounding affects about 450 USAF F-15A-Ds, and could spread to Boeing's overseas customers, such as Israel, Japan and Saudi Arabia.
The USAF eventually intends to replace a portion of the F-15C/D fleet with the Lockheed Martin F-22A, but about 179 aircraft of the type are planned to remain in service through 2025. More than 200 F-15Es, meanwhile, are scheduled to be retired after 2030.