An engineer once employed by defense contractor Lockheed Martin Corp. is claiming in a federal lawsuit that the company knowingly used "defective" stealth coatings when building its F-22 Raptor jets.

Darrol Olsen says in the lawsuit that between September 1995 and June 1999 Lockheed had "falsely certified" the coatings, saying they had passed stealth tests and concealed test results that showed otherwise.

Olsen says in court filings he was told to "stay out of it" when he complained about the issue to his superiors.

Lockheed says in a statement that the allegations have no merit and it will "vigorously defend this matter in court." The Air Force did not immediately issue a comment.

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