all air worth niness directives were complied with and were up to date. >> reporter: because those earlier inspections found nothing, it's calling into question the nation's entire system for inspecting older aircraft. >> i think this could really move the bar up a bit. we may have to change when we start inspecting these aircraft. we did not expect to see this type of failure occur in an aircraft this young. >> reporter: could this have really caused the plane to crash, this crack? >> anytime a cabin opens up in a passenger airline at 36,000 feet, it's bad and it's potentially catastrophic. this had a happy ending. the indents in the past have had happy endings. at some point you can get to the point where there's structural failure on the aircraft because the skin on the aircraft is part of that structural foundation of the aircraft. >> reporter: the large section that failed? on tuesday, investigators will begin a microscopic examination of the metal as they try to piece together what happened. for "nightline," i'm lisa stark, in baltimore. >> lisa has been on this story since it broke