ST. LOUIS -- The Air Force released animation on Wednesday of an F-15 fighter jet crash near Salem, Mo., that led to the grounding of the entire fleet in November. The animation shows the jet breaking apart during a training exercise.

An Air Force report concludes a defective metal beam in the frame of the F-15 cracked, causing the crash. Major Stephen Stilwell ejected from the plane but suffered significant injuries.

The incident led to the grounding of the F-15 fleet. Some were cleared to return to the air on Wednesday. The Missouri Air National Guard resumed F-15 flights on Thursday. Col. Robert Leeker, commander of the 131st Fighter Wing, said one F-15 in St. Louis was found to have the cracked metal beam.

Stilwell says his career is on hold as he undergoes extensive rehabilitation for serious injuries to his left arm and shoulder. The rehab likely will take about a year.