Earlier in April, a hole opened up in the roof of the jet, forcing an emergency landing.
ABC News has learned that part of the problem may have been a defect when the Boeing plane was manufactured in 1996.
Investigators believe thousands of metal pins that hold the airplane together were not sized correctly, and over time, that's what caused cracking in the metal.
Meantime, the damaged plane has been patched up and is expected to go back into service.
