By Michael Sirak
The Air Force on Wednesday stood down its single-seat F-15A and F-15C Eagle fighter aircraft and F-15B and F-15D two-seat trainers for the second time this month pending new safety inspections, according to Air Combat Command (ACC).
The stand-down, the command said, does not affect the Air Force’s F-15E Strike Eagle multirole fighter jets, which are newer and somewhat structurally different than the Eagles.
ACC Commander Gen. John Corley made the decision on Nov. 28 after results came back the previous day from metallurgical tests of the Missouri Air National Guard F-15C that crashed at the beginning of the month. The test results indicated a potential fleet-wide airworthiness issue surrounding the F-15’s upper longerons near the canopy of the aircraft. The longerons, which are major structural components running along the length and side of the aircraft, appear to have cracked and failed, ACC said.
“Based on those new findings, all F-15 A through D models will undergo a stand down that will require additional inspections and possible repair actions,” the command wrote Nov. 28.
The duration of the stand-down is pending the completion of the inspections and any necessary repair actions, ACC said. Each Eagle will undergo a tailored inspection of the upper longerons in the area of concern, the command said.
The stand-down came only about one week after Corley had authorized the F-15A/B/C/Ds to return to flight status after undergoing a safety inspection. The Air Force grounded its entire fleet of F-15s, about 670 aircraft in total, on Nov. 3 after the F-15C crash on the previous day, since the mishap pointed to a catastrophic structural failure to which other F-15s might be susceptible. The grounding affected not only the 440-plus F-15A/B/C/D air superiority fighters, but also the Air Force’s 224 F-15Es.
After preliminary analysis conducted by the accident investigation board, ACC allowed at first the Strike Eagles and then the Eagles to return to flight status after each aircraft underwent an inspection (Defense Daily, Nov. 14, Nov. 19 and Nov. 27).
However, based on the new information, ACC said Wednesday’s stand-down was warranted.
“We have a lot more information now,” ACC spokesman Maj. Tom Crosson told Defense Daily. “We have levels of details now that we didn’t have immediately after the mishap.
“In this circumstance,” he continued, “we have engineers reporting to us and saying they are finding cracks in this particular area consistently. There is no speculation.”
Indeed, “manufacturer simulations have indicated a catastrophic failure could result in this particular area,” ACC wrote. Recently cracks were discovered along the same longeron area during two inspections of F-15C aircraft, prompting their immediate grounding, the command noted.
ACC said although the longeron area was covered in general by previous inspections as a result of the Nov. 2 crash, technical experts at the Warner Robins Air Logistics Center in Georgia are recommending a specific inspection technique for the suspect area based on the findings of the metallurgical tests.
In the interim, ACC said it continues to work with the Air National Guard, Air Force Reserve, U.S. Air Forces in Europe, Pacific Air Forces as well as joint and coalition partners, to ensure mission coverage of the gaps caused by the F-15 stand-down.
The Air Force says there is a difference between grounding aircraft, as happened with the F-15s on Nov. 3, and standing them down, as occurred on Nov. 28.
ACC spokeswoman Tech. Sgt. Cindy Dorfner told Defense Daily yesterday a stand-down generally provides commanders time to assess an incident or finding and the actions required to safely resume operations. Conversely, groundings are typically linked to specific maintenance actions, she explained in a written correspondence.