What was found
AFTER REPLACEMENT OF THE NR 1 CARBON SEAL ON AIRCRAFT 7123 LEFT ENGINE 807393, A CRACK WAS DISCOVERED ON THE FAN DISK AT THE FORWARD 12:00 POSITION OF THE NR 21 FAN BLADE PIN RETAINING BORE. THE CRACK IS APPROXIMATELY 1.5 INCHES IN LENGTH AND EXTENDS FROM THE FORWARD/TOP TO THE AFT/TOP OF THE BLADE RETAINING PIN BORE. THE NR 21 BLADE RETAINING BUSHING ON THE DISK IS EXPOSED ON THE FRONT SIDE AND RECESSED ON THE AFT SIDE APPROXIMATELY .056 . REMOVED AND REPLACED FAN DISK AND ALL FAN BLADES.