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December 10, 2007— The F-15A-D fleet is in far worse shape than inspections of even a month ago revealed, according to top Air Force leaders. These earlier model F-15s have been grounded almost continuously since a 27-year-old F-15C broke up during a mild maneuver on Nov 2. Continued inspections, analysis, and computer simulations run since that crash have identified likely culprits—the “band-aids” applied over the years to fix smaller cracks. So far, the service has found eight aircraft that are "hard broke." Inspections continue. 

The initial F-15 design allowed a certain degree aircraft flexing, but as the fatigue-stressed tail structure received splices and stiffeners and were beefed up or banded with metal straps to keep the airplane together, the patched areas got more rigid. The aircraft’s natural torque shifted to areas of the longerons that were never expected to bear those loads. Worse, it looks like the affected areas weren’t routinely inspected because they weren’t supposed to be subject to torque. Even worse, some of the load has spread out to the F-15’s skin itself, and years of removing and re-attaching access panels has made the skin a dubious bearer of aerodynamic flex.

USAF has ruled out bad maintenance, bad part lots, bad manufacturers, or bad production periods, as the affected aircraft are of various vintage and production groups. Eight aircraft so far have been condemned as “hard broke,” meaning they can’t be economically repaired. Inspections continue.
“Fooling Itself”
One top leader admitted that the Air Force has been “fooling itself” that it could push the Eagle fleet so far past its intended mid-1990s retirement, delegating it to less-stressing missions. The initial plan called for the F-22 to reach squadron strength in the early 1990s. It is now 17 years later, and “the piper must be paid,” one top official said.

Incidentally, the F-15Es and later export models such as the F-15I for Israel and F-15K for South Korea are still flying because lessons learned from the A-D fleet were incorporated into their design. They are not suffering from the same problems. The Air Force cleared the E model, built for the highly stressful close air support mission, on Nov. 11.
Lengthening Window of Vulnerability
Even if the grounded F-15s were all cleared to fly again today, it would still take six months to re-qualify F-15 pilots who have mostly been unable to fly for six weeks, top service leaders said. The Eagle pilots certainly won’t be able to resume flying until mid-January, if then, as the Air Force has decided not to fly until the Accident Investigation Board completes its report. That would normally come within about 60 days, but the AIB is likely to get a waiver to take longer.

In the meantime, F-15s are not only prohibited from flying combat air patrols for homeland defense, they aren’t participating in joint-force exercises like Red Flag, and the F-15 schoolhouse at Tyndall AFB, Fla. is idle. That means proficiency across the force, as well as the flow of replacement pilots, is being badly disrupted, and it won’t be easily or quickly brought back up to speed.

Simulators can help keep the pilots from thoroughly losing the ball, but there are typically only a couple at any base, vs. dozens of real aircraft on the flight line. Sim time is also considered an inadequate substitute, especially for landing qualifications. Some F-15s are available to fly if combat commanders deem it crucial, such as in the US Central Command area of responsibility.
What Now?
Technical experts at USAF's F-15 depot, the Warner Robins Air Logistics Center in Georgia, are working to complete new inspection techniques for field units to use. Right now, maintainers at F-15 units are working through current intensive inspections. They will continue inspecting each aircraft once they receive the new procedures, which the ALC is basing directly on findings from investigation of the pieces of the aircraft that crashed.

Once units have completed inspections of each aircraft, those F-15s that USAF thinks can be economically fixed will get repaired at WRALC. A top USAF official said the ALC can fix the F-15s “faster and cheaper” than Boeing, which is the prime contractor for the Eagle.