First entering servicein the 1980s, thetwin-enginefighterplanewasthe U.S.'sfirststrike fighter - an aircraft capable of attackingboth ground and aerialtargets.
There were new designs for the plane's rocket engine, landing equipment and the small rockets needed to move it in space.
VOA: special.2010.07.07
Extensive tests on the plane's engine revealed the crack was a result of the "unique operating environment" of the test flight, and was not a widespread issue, he added.
The cause of the crash has not yet been officially confirmed but Mr Shahi said he had been informed the plane's engine burst into flames after being hit by a bird.
The plane's left engine, which detached from the plane, evidently upon impact with the water, was found Wednesday in about 50 feet of water, and recovery is expected sometime Thursday, the NTSB said.