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January 10, 2008— The Air Force anticipates having 290 of its F-15 A-D models return to flight status today. This will still leave roughly 150 of its Eagles on stand down. All of these remaining aircraft, Air Combat Command says, have been found to have some kind of “issue” with fatigue stress.

Indeed, these airplanes “have at least one longeron that does not meet blueprint specifications” and will require additional evaluation, ACC writes in yesterday’s release on clearing some F-15s for flight. Engineers at Warner Robins Air Logistics Center will analyze these deviations over the next month to determine which of these aircraft will require repair or additional inspection before a return to flight, ACC says.

But are they worth fixing? The issue has certainly ignited the debate over whether it makes more sense to invest in modern airplanes (read as: more than 183 F-22s) vice continually pumping dollars into older platforms that have already exceeded their design lives and are increasingly more ornery and costly to maintain.

The Los Angeles Times reported yesterday that the Air Force is considering grounding “dozens” of these remaining F-15s permanently. 

“Do you try to patch a 25-year-old airplane that has been patched and patched and patched?” it quoted a senior Air Force official as asking. “After the repairs, it will not be the same aircraft it was before.”

The Daily Report has learned that USAF senior leaders believe 159 F-15s may never fly again.

To date inspections have turned up nine F-15Cs with fatigue cracks in their longerons, the structural support beams around the cockpit. (The nine aircraft are: two F-15Cs at Kadena AB, Japan; one at Tyndall AFB, Fla.; four Air National Guard F-15Cs at Kingsley Field, Ore.; and one ANG Eagle each at St. Louis, Mo., and Barnes Airport in Westfield, Mass.) The structural failure of a longeron is the most likely cause of the Nov. 2 Air Guard F-15C crash that led to the fleet’s stand down.

These nine aircraft are currently “broke,” Air Force officials say. To fly again, they would require new longerons, a 40-day-plus fix estimated to cost about $200,000 per aircraft.

Like those nine airframes with cracks, the remaining F-15s may require new longerons. Or they may be cleared for flight upon closer examination. ACC spokesman Maj. Tom Crosson tells the Daily Report that this will depend on the outcome of the forthcoming evaluations and inspections.

The Air Force had plans on the books before the longeron issue surfaced to start retiring some F-15s starting in 2009 so a phaseout of some Eagles is not unexpected in the near term, Crosson said. USAF might juggle the order of retirement of the tail numbers to mitigate the impact of the longeron issue.

Nonetheless, this issue is not trivial. Yesterday’s Times piece quotes Defense Secretary Robert Gates as acknowledging the seriousness of the F-15 fleet’s condition, among the aging aircraft challenges that USAF is facing.

“The Air Force's top priority has to be the replacement of the tanker fleet, but I think the notion that the Air Force is somehow pumping up the F-15 problem, I just don't believe that for a second. I think it's a real concern,” Gates said, according to the newspaper article.

The F-15 A-D models average 25 years in age. The Eagle entered service in 1975 about three years after the Navy’s F-14 Tomcat fighter aircraft, which the sea service retired in 2006. Conversely Eagles are expected to remain in use for about two more decades. Comparatively newer two-seat F-15E Strike Eagle multirole fighters have not been under the same restrictions due to a reinforced airframe to accommodate carrying bombs.