Sources: Wrongly-sized rivet holes caused hole in Southwest's 737
SEATTLE -- It was a harrowing moment at 34,000 feet when the skin of the Southwest jet opened up a 5-foot hole on April 1. Passengers could see daylight as oxygen masks dropped and the pilot began to dive to a lower altitude.
Investigators found widespread cracking in the metal, which was initially though to be metal fatigue that resulted from the plane's 39,000 takeoffs and landings.
But ABC News has learned that in fact, the part of the problem may have actually been a defect when the Boeing plane was manufactured in 1996.
Investigators are focused on rivets -- the thousands of metal pins that hold the pieces of an airplane together. The concern is that in the area that failed, those pieces were not held together as they should have been.
At this seam in the fuselage - where one piece of metal overlapped another, sources told ABC News some of the rivet holes were not sized correctly, that two pieces were not fastened together tight enough at the seam. Over time, it's believed, that stressed the area and resulted in the cracking.
Even as the investigation continues, that damaged plane has been patched, and it's expected to go back into service.
After this incident, Boeing ordered inspections of similar 737s worldwide, nearly 600 in all. But 190 were required to have inspections right away. Boeing says 75 percent of those planes have been looked at, and only five - all Southwest jets - were found to have slight cracks. Sources say most of those five planes were built about the same time as the aircraft that came apart.
Boeing on Friday said it had not received an update from the National Transportation Safety Board and as a result, could not comment.
"No conclusions have been reached about root cause of the inspection findings, nor of any relationship to the April 1 event. Any attempt to draw conclusions on either would be premature and speculative," Boeing said in a statement.
Investigators found widespread cracking in the metal, which was initially though to be metal fatigue that resulted from the plane's 39,000 takeoffs and landings.
But ABC News has learned that in fact, the part of the problem may have actually been a defect when the Boeing plane was manufactured in 1996.
Investigators are focused on rivets -- the thousands of metal pins that hold the pieces of an airplane together. The concern is that in the area that failed, those pieces were not held together as they should have been.
At this seam in the fuselage - where one piece of metal overlapped another, sources told ABC News some of the rivet holes were not sized correctly, that two pieces were not fastened together tight enough at the seam. Over time, it's believed, that stressed the area and resulted in the cracking.
Even as the investigation continues, that damaged plane has been patched, and it's expected to go back into service.
After this incident, Boeing ordered inspections of similar 737s worldwide, nearly 600 in all. But 190 were required to have inspections right away. Boeing says 75 percent of those planes have been looked at, and only five - all Southwest jets - were found to have slight cracks. Sources say most of those five planes were built about the same time as the aircraft that came apart.
Boeing on Friday said it had not received an update from the National Transportation Safety Board and as a result, could not comment.
"No conclusions have been reached about root cause of the inspection findings, nor of any relationship to the April 1 event. Any attempt to draw conclusions on either would be premature and speculative," Boeing said in a statement.
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