Lockheed denies such claims, however, and says "our supplier base is the best in the industry."

The plane's famed 'gold canopy' a million-dollar, radar-absorbing cause of envy for other fighter pilots has also caused problems. A stuck hatch imprisoned a pilot for hours in 2006 and, to date, engineers have been unable to extend the canopy's lifespan beyond about 18 months of flying time.

Ex-Pentagon official Ahern and Air Force Gen CD Moore, have both confirmed that canopy visibility has been declining more rapidly than envisaged, forcing $120,000 of repairs at 331 hours of average flying time, instead of the stipulated 800 hours.

The plane's first operational flight test in September 2004 saw it meet two of 22 key requirements and display a total of 351 deficiencies. In 2006, it fully met five, and in 2008 when the sixth squadron was fully deployed, the Raptor had fully met seven key requirements.

Pentagon officials stress that the F-22s are on track to meet all its key performance parameters by next year.