(US) Air Force Fighter Fleet in 'Crisis'

WASHINGTON (AP) — Years of stress on the Air Force's aging jet fighter fleet have led to serious structural problems that could grow worse even after expensive repairs are made, senior service officials said Thursday.

Gen. John Corley, the top officer at Air Combat Command at Langley Air Force Base, Va., called the situation a "crisis" that would be best solved by an infusion of costly new aircraft rather than fixing jets that are 25 years old.

The mechanical troubles, most acute in the F-15 Eagles used to protect the United States, also have led to a patchwork approach to filling critical air missions at home and in Iraq and Afghanistan.

With nearly a third of the F-15 fleet grounded due to a defective support beam in the aircraft's frame, other fighter aircraft, including F-16s and new F-22s, are being shifted from duty in Iraq and Afghanistan.

"It's a rob Peter to pay Paul," Corley said at a Pentagon news conference. "It's unprecedented to have an air superiority fleet that's on average 25 years old."

The Air Force's dilemma has been largely overshadowed by the equally urgent demands from the Army and Marine Corps for new equipment to replace the battle gear worn down by more than six years of war. That changed on Nov. 2 when an F-15C aircraft broke in two during a training flight over Missouri.

The pilot, Maj. Stephen Stilwell, barely had time to eject from the front half of the F-15. His left shoulder was dislocated and his left arm shattered as the cockpit blew apart.

An investigation of the crash released Thursday concluded that a defective aluminum beam in the frame cracked, causing the $42 million jet to disintegrate in the air. There was no pilot error.

More troubling, however, were the findings of a parallel examination that determined as many as 163 of the workhorse F-15s also have the flawed beams, called longerons. The aircraft remain grounded as the Air Force tries to determine how broad the problem is and whether fixes should be made. Another 19 of the aircraft have yet to be inspected and also remain grounded.

In the report on Stilwell's crash, Col. William Wignall, the lead investigator, said that prior to Stilwell's flight, "no inspection requirements existed for detecting a crack in the longeron."

The F-15A through D models were built by McDonnell Douglas. That company merged with the defense manufacturing giant, Boeing Co., in August 1997.

The faulty longerons "failed to meet blueprint specifications," according to the Air Force. No decision has been reached as to whether Boeing might be liable for the repairs, however.

"This is the starting point of answering that question," said Lt. Gen. Donald Hoffman, a senior Air Force acquisition official. "So now that we have the evidence of what happened in (Stilwell's) case, it will all boil down to what our contractual relationship was with the manufacturer at the time."

Nearly 260 of the A through D model F-15s, first fielded in the mid-1970s, were returned to flight status Tuesday following fleet-wide inspections.

The Air Force's fleet of 224 newer F-15E Strike Eagles do not have defective longerons. Those jets, whose role is more oriented toward ground attack missions, were temporarily grounded after Stilwell's crash, but returned to service shortly thereafter.

The longeron helps support the cockpit and strengthen the jet as it moves through high-stress maneuvers while traveling hundreds of miles per hour.

Corley said even if the longerons in the older F-15s are replaced — a procedure that costs $250,000 per beam — there's no guarantee that other parts won't go bad.

"You may wind up with an airplane that is already so far beyond it's economic service life, that to throw a quarter of million dollars at it to replace a bad part may be a bad idea," he said. "That may be buying way too much risk. We've already bought too much risk because we've bought too little iron over the years."

The F-16, fielded in the late 1970s, is undergoing an extensive modernization program, Corley said. So, too, is the tank-killing A-10, a 30-year old plane used to support troops on the ground.

The Air Force has fielded more than 90 F-22 Raptors, a stealth fighter made by defense contractor Lockheed Martin Corp. But these aircraft cost $160 million apiece and the Pentagon has decided to buy only 183. The Air Force has said it needs 381 F-22s and has support on Capitol Hill for a larger acquisition that would keep require tens of billions of dollars.

The F-35 Lightning is another new fighter that is being built but won't be in use for several more years.

"I flew this airplane 30 years ago," said Corley, an F-15 instructor pilot in 1979 when he was a captain. "It was best of breed at its time. It's not anymore. All options on the table, yes. But is it where I would turn to now? No."

By contrast, the F-22 is a modern plane that meets the Air Force's needs for an air combat jet, he said.

"The hot running production line that the United States Air Force has right now for fighter aircraft is the F-22," Corley said. "That line has the capacity. So you'd have to ask yourself, 'Can I buy F-22s?'"

"We are operating a fleet of aircraft to battle the now defunct Soviet Union, except our current enemies are uneducated, third world thugs armed with AKs and RPGs.

Wait until China get their military upgrades completed in the next decade."

We don't stand a chance against China now or 10 years in the future if we try to stay conventional, we will inly go broke trying to prepare for a conflict we can't win.

Look at the news article today about China "only" having 100,000 workers killed in on the job accidents THIS YEAR! And they say this is good because it represents a reduction (10%) fom last year.

If China trys a land grab anywhere in the world, they will be sucessful unless Nukes are used early and often against them. Plus, they understand the theory of strategic attack as opposed to our reliance on tactical attack only.

If you ask a teenager if he wants a low end pickup or a Ferrari as his work truck, they will pick the Ferrari every time. We need to stop letting these jetjocks pick their dream hotrods (unless they want to foot the bill.).

I was looking for an article that gave the flight hours of the mishap F-15 that forced this grounding, and here is finally is. Sounds to me like this one definately did not make it's numbers.

Manufacturing defects caused cracks that downed USAF F-15

Fatigue cracks started by manufacturing defects in a fuselage longeron caused the in-flight break-up of a Boeing F-15C Eagle on 2 November 2007, the US Air Force accident investigation has concluded.

Longeron cracks have been found in another nine F-15Cs, and manufacturing defects that could potentially cause fatigue cracking have been detected in a further 182 F-15A-Ds. All of these aircraft remain grounded.

Examination of the wreckage of the crashed F-15 revealed the right upper longeron, a critical load-carrying component in the forward fuselage, failed because of a fatigue crack that formed where the metal was thinner than specified in the blueprint.

Instead of being the specified 0.090-0.110in (2.3-2.8mm) thick, the flat top, or web, of the aluminium longeron that failed was as thin as 0.039in – less than a millimetre - in the area when the fatigue crack formed.

The thinning was caused when the longeron was machined by McDonnell Douglas during production of the aircraft, which was delivered in 1982. Similar manufacturing defects - undercuts, ridges or surface roughness that could potentially cause stress concentrations – have been detected in upper longerons in 40% of fleet.

This was by far the worst thinning of a web discovered by the fleet-wide inspections that followed the crash, says Maj Gen Thomas Owen, commander of Warner Robins Air Logistics Center, the USAF’s F-15 depot.

The accident aircraft had accumulated 5,700 flight hours, says Owen, or 11,000 “equivalent spectrum hours” taking in account the additional fatigue stress imposed by high-G manoeuvring. But the longeron was projected to last 31,000h, well past the life of the aircraft, he says.

In the 2 November in-flight break-up, the cockpit separated at canted fuselage station 377, where the forward and aft sections of the two-piece upper longerons are spliced. The fatigue crack had formed just forward of the splice, in an undercut produced when a sloping transition was machined in the underside of the longeron.

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.

The "real solution" to the aging F15 needs to be implemented before the F15s are so worn out as to be useless. There needs to be an overlap period.

All sorts of plans get tossed out the window when an unexpected flaw threatens to ground the backbone of the USAF air supremacy fleet. All of a sudden, the luxury of knowing there will be enough F15s on hand for another 10-20 years gets thrown out the window. That brings up more questions. Speed up F16 upgrades? Increase capacity to make more F22s faster? Start a crash program to get UAVs to replace the missing F15s?

Even if it costs "only" $1million to fix each each F15, you just don't mail the parts out to each squadron, and have them install it on a weekend. The part will have to be designed, and then tested to make sure it fixes the original problem, and doesn't introduce new ones down the road. Each F15 will have to be flown, gently, back to the factory, or a major depot, and be torn down into little pieces and then reinstalled around the new longeron. Who knows if there will be other nasty surprises waiting when a more complete teardown is done?

If they had a part designed today, and a fixed price to do the repair, it would take a couple of years to cycle all of the aircraft through the system. That would then bring us right back to where we were before that F15 broke up in mid air: how many new F22s should we build? What is the role of UAVs? How much time do we have to debate these questions before it's too late, and we have to work with whatever we have on hand at that moment?

And those wonderful B52s, still flying after 50 years, are still in the air because a lot of money was spent to upgrade and fly them, and because there are 500 or 600 older B52s in the boneyard available to strip for parts that can no longer be made for any amount of money. This wasn't some grand design of the USAF, it was a matter of survival when follow-on bombers were never produced in enough numbers to take the load off the B52.

I assume you read my post #85. The accident aircraft had "accumulated 5,700 flight hours ... or 11,000 “equivalent spectrum hours”".

Also, the longeron that failed was 0.039 inch thick at the point where it failed, where the spec called for 0.10 inch plus or minus 0.01 inch. That's only 40% of the specified thickness.

The part did not meet it's manufacturing tolerance (thus was defective) and did not meet it's design lifetime (quoted as 31,000 hours.)

It was 40% of the thickness it should have been, and lasted 40% as long as it should have.

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