Well we have a answer as to why the 9 F-15s that where found with forward longeron cracks. Its seems to be a problem in manufacturing.
Cracks were found in nine other F-15s where machining during manufacture had reduced the thickness of the longeron web below blueprint
specification or where there is surface roughness that could cause stress concentration.
And the go on to expand that the 40% that are still grounded may not fly again. Then they mention the 16s and A-10s but personally they need to be
more concerned with the KC-135s which are in a much worse position. Though it is true they are not subject to the same extreme g-forces etc.
"I have a fleet that is 100% fatigued, and 40% of that has bad parts. The long-term future of the F-15 is in question," says Gen John Corley,
commander of Air Combat Command. "The problem is systemic and goes beyond the F-15," he says, citing fatigue issues with A-10s and F-16s.
While the USAF has not decided which, if any, aircraft will be repairs, Warner Robins is manufacturing an initial batch of 15 longerons at a
cost of $15,000. Owen says replacement of the longeron in an aircraft will cost $250,000.
Im assuming that is minus man hours and down time etc. Investigators say the crack started on the underside of the longeron, working its way upwards
and outwards through the over-thin web until it reached the outer “posts”, which carry the bulk of the forward fuselage loads.
www.flightglobal.com...
[edit on 11-1-2008 by Canada_EH]