But pilots are not the only Airmen raving about the Raptor. Maintainers are finding the Raptor's new technology a quantum leap over the legacy systems of the past.

"The Raptor [contains] fourth-generation stealth technology and has a fully integrated avionics suite, yet it remains the most maintenance-friendly airplane ever," said Capt. Rognald Christensen, the 43rd Aircraft Maintenance Unit?s officer in charge.

One maintenance-friendly feature is the portable computer that hooks directly into the aircraft. It enables maintenance crews to conduct operational checks on the ground, eliminating the need to get into the cockpit during engine runs. It also contains a library of 1,300 technical orders.

Integrating technical orders with maintenance tasks ensures fingertip access to information and that each step is completed correctly before allowing the maintainer to proceed, Captain Christensen said.

Easy access to components is another feature. On other aircraft, changing components is not a maintainer-friendly experience, said Master Sgt. Richard Street, the 43rd Aircraft Maintenance Unit section chief.

"On the Raptor, I don't have to remove one component in order to reach another," Sergeant Street said.

Interesting to see what the thrust vector nozzles add to the maintenance equation. Example: I think the TV nozzles on a SU-30MKI need some kind of maintenance procedure at 100 hours. I just don't know what that involves.

When asked what effect age has on aircraft, U.S. Air Force Staff Sgt. William Pyle pushed his wire-rimmed glasses up the bridge of his nose, shook his head and chuckled.

"Where do you want me to begin?" he asked.

Pyle is an F-15 Eagle maintainer who, for the past eight years, has worked to keep Langley's fighters airworthy. He helps inspect the aircraft after every 200 hours of flight - and that job is getting more difficult every year, Pyle said.

As the aircraft get older, more in-depth inspections are required. More panels have to be pulled off the airplanes to check for internal cracks and corrosion that might have cropped up. It's the law of numbers, Pyle said. The more problems you look for, the more you will find.

Pyle is not alone in his fight. Practically every maintainer of every airframe is facing similar troubles. The Air Force's aircraft are aging at a rapid rate. Fighters are an average of 19 years old, the average bomber is about 22 years old and the KC-135 tanker fleet is pushing 50 years, according to data provided by the service.

Air Force leaders say they are taking steps to solve the aging aircraft dilemma, but a high operational tempo and shrinking budgets are hampering progress.

For Pyle and his peers, the outlook is grim.

From F-15 fighters to C-5 transports to MH-53 Pave Low helicopters, the service is operating a rapidly aging fleet.

The average age of the operation force is "something like 22.7 years," according to James Roche, Air Force secretary. The problems that come with age are showing throughout the service, he said.

If the Air Force respects its elders, then the KC-135 Stratotanker is arguably the most respected aircraft in the fleet. It entered the inventory in 1956, but the average KC-135 is 42 years old.

"Close to half of the KC-135Es that are flying today were flying when I was commissioned ensign," said Roche, who entered the U.S. Navy in 1960, according to his biography.

Out on the flight line, maintainers are finding leaks in the fuel bladders. Corrosion on the engine struts is causing depot workers to spend thousands of man-hours grinding out the decaying metal.

The KC-135E's depot work package has doubled in the past 13 years, an Air Force spokesman said. In 1991, it took 17,000 man-hours to get just one aircraft through the depot. In 2003, that number jumped to 35,000.

Maintainers can expect the numbers to get worse. Richard Aboulafia, vice president of analysis for the Teal Group, a Fairfax, Va.-based think tank, said that's one thing almost everyone can agree on.

"Per flight hour, certainly, as the fleet ages, you will have to spend more both in terms of money and man-hours," Aboulafia said.

The situation will only get worse unless the Air Force retires large numbers of its aging weapon systems, he said.

Even when problems are located, fixing them is not always easy. The aircraft are so old that it's difficult to get some spare parts because the original manufacturers are no longer making them or have closed down altogether.

So jets that are already down for maintenance are cannibalized and their parts used to fix other aircraft. And with increasing frequency and innovation, maintain-ers also have started to make parts from scratch.

Past Their Expiration Dates

Despite the relentless efforts of maintainers and depots, planes are starting to show their age.

Since 1991, the KC-135 fleet's mission-capable rate - the percentage of aircraft that are available for their mission at any given time - has declined. In fiscal 1991, the KC-135 fleet had a mission-capable rate of 82.4 percent. Thirteen years later, the rate has dropped to 77.3 percent.

The F-15s have experienced a similar decline, going from 81.2 percent in 1991 to 74.6 percent in 2004.

As the F-15s get older, the maintainers have to conduct more intensive inspections, or "phase dock" in maintenance jargon. The number of "work cards" or checklists of tasks that must be accomplished has more than doubled in Pyle's eight years here.

The average F-15 is 17.8 years old, according to data provided by the Air Force. But Pyle and his colleagues at Langley have to deal with jets that are almost 30.

It's not just the number of years that causes problems. It's the number of flight hours and the type of flying being done in the F-15 that are degrading the aircraft's structural integrity.

"It's just like when you take your car in for service," Pyle said. "Look at your driver's manual and see what's required for a 30,000-mile inspection vs. the 100,000-mile inspection."

More panels have to get opened up, which means they have a greater chance of finding more problems such as corrosion and wire chafing.

And cracks.

Because the F-15 flies in a high-stress environment and has to sustain multiple G maneuvers, the airplanes are cracking.

"We know that when these aircraft come in, they're going to be cracked, stressed, fatigued [and] leaking," Pyle said.

To prove his point, Pyle knocked on the side of an engine inlet, one of the most hollow parts of the aircraft.

"Do you hear that twang?" he asked. "There's a crack there."

In July, with temperatures climbing to 100 degrees and sweat beading off his brow, Pyle crouched under the belly of an F-15 to point out more cracks. The vertical tails also are vulnerable to cracking, he said.

"Instead of finding one or two cracks, we're finding 10," Pyle said, comparing the numbers from when he began working on the jet to today. "Cracks on the intake are an everyday thing."

To fix the cracks, sheet metal experts have to cut holes in the plane to see what's going on behind the outer skin. Once the metal is removed, maintainers can find a variety of problems. Around the wings where the fuel is stored, corrosion and leaking often occur.

"The older these jets get, the more work we have," said Staff Sgt. Derek Aubuchon, a sheet metal expert at Langley. "They're not like wine. They don't age well."

Over time, the metal becomes more brittle and worse at handling the G forces that push against the plane during high-stress maneuvers, Aubuchon said. The phenomenon is called fatiguing.

"The jets can take less and less over time," he said.

To repair a crack, Aubuchon creates a metal patch to cover the hole he makes to inspect behind the crack. The metal he uses is thicker than the rest of the aircraft skin, which puts more stress on the surrounding structure.

It's not uncommon to see a row of patches - some of which are 30 square inches or bigger - down the side of an engine inlet, Aubuchon said.

And this problem will only worsen with time.

"My personal opinion is that these jets weren't supposed to fly this long," Aubuchon said. "They've passed their expiration dates."

Officials from the Aging Aircraft System Program Office at Wright-Patterson Air Force Base, Ohio, seconded Aubuchon's opinion and said fighters are being flown well past the age when they were initially intended to be retired.

As a result, issues that engineers and maintainers never would have expected now crop up daily.

The F-16 Fighting Falcon, for example, is seeing more frequent cracks on the landing gear and throughout the fuselage.

F-16 maintainers at Luke Air Force Base, Ariz., are discovering chafed wiring - something they never anticipated and have no set protocol to fix.

These problems are "due to the operation of many aircraft in excess of their original projected service life," Air Force officials wrote in response to questions.

And the F-16s are not alone.

The A-10 attack jet has encountered split layers and cracks in the flight control surfaces, and corrosion around the fuel cell floor. The C-141 airlifter has fuel system leaks. The C-130 Hercules has "increasing ?aging aircraft' issues such as corrosion [and] cracking," officials also wrote.

Cutting Aircraft To Cut Costs

Isolating the cost associated with aging aircraft is difficult. But no one denies the basics of aircraft math: The older an aircraft is, the more expensive it is to maintain.

"In certain of our aircraft, the cost to maintain is going up by 10 percent a year. And that includes inflation, so that's 7 percent real," Roche said, referring to cost per flying hour for the C-5 fleet.

"You can keep old planes going, but they tend to cost more in maintenance, like keeping an old car going," Roche said.