Originally designed and built to replace other fighter and ground attack aircraft in the U.S. military's arsenal, the radar-evading F-22 is an evolutionary dead end. The Air Force acquired only 188 of them from aerospace maker Lockheed and doesn't plan to have any more produced.

Even though they formally came into service in 2005, the F-22 had been grounded repeatedly because of what were indeterminate causes that resulted in pilots losing consciousness in the air.

U.S. military's fighter fleet

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The Air Force is confident it solved the problem, but some top pilots still refused to fly the plane, citing safety concerns.

Today, the Air Force has 187 of the fighters after one crashed in 2010, killing the pilot. A subsequent report by the Pentagon watchdog found the Air Force initially blamed the crash on pilot error when in fact a mechanical error was at fault.

The F-22 has also been accused of causing a mysterious illness in mechanics charged with maintaining it.

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Last year, the Air Force lifted all flight restrictions on the F-22, saying the plane is now safe to fly.

The military's other prized fighter program, the F-35 fighter-bomber, has faced similar questions about massive cost overruns and mechanical problems.