A source familiar with the investigation told SPACE.com that investigators had discovered that the doomed shuttle was outfitted with a pair of faulty bolt-catchers. Manufactured by SUMMA Technology, Inc., bolt-catchers are dome-shaped devices designed to capture the frangible, or fracturable, bolts that attach the vehicles twin solid rocket boosters to the orange external tank.

Each solid rocket booster is equipped with a bolt-catcher to secure the large, heavy bolts, which are broken in half to release the spent solid rocket boosters from the external tank about two minutes after launch. The catchers are meant to prevent the broken bolt segments from striking the vehicle Investigators closing out the so-called fault tree of possible sources of debris that could have struck Columbia during its climb to orbit were unable to verify that one of the vehicles bolt-catchers had operated properly, raising the possibility that the orbiters wing may have also been struck by a wayward bolt.

There is no telemetry or visual evidence that such an incident occured. 

But more troubling to the CAIB is the fact that the faulty hardware somehow slipped through the quality control inspection process, which had hard evidence the equipment was faulty. The Board requested that NASA inspect and test a similar flight-qualified bolt-catcher awaiting installation on a future shuttle.

Tests revealed that the bolt-catcher failed under far lower stress load levels than it was designed for. X-rays of the bolt-catcher were then scrutinized and found to clearly show the device to be defective. Investigators determined that this particular bolt-catcher should have never passed inspection, yet it carried an approved for flight tag signed by a quality assurance inspector.

It is unclear whether that inspector worked for NASA or the prime shuttle contractor, United Space Alliance. Investigators then pulled the x-rays for both of Columbias bolt-catchers. Closer inspection revealed that both bolt-catchers installed on Columbia were also clearly defective; yet again, both devices were approved as flight qualified.

According to the source, this discovery does not change the CAIB's overall scenario that insulating foam from the external tank broke off and struck Columbia's wing, possibly -- although still not conclusively -- damaging the wing and setting up conditions that led to the Feb. 1 disaster in which all seven astronauts were lost. The CAIB is scheduled to hold its first Washington, D.C. press briefing beginning today a 1 p.m. EDT (1700 GMT).