As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE NR 1 ENGINE SPOOLED DOWN ACCOMPANIED BY A LOUD EXPLOSION WHILE CLIMBING THROUGH FL 310. ABNORMAL PROCEDURES WERE COMPLIED WITH AND THE AIRCRAFT WAS RETURNED TO SFO WHERE IT LANDED WITHOUT INCIDENT. THE NR 1 ENGINE WAS REMOVED AND REPLACED. THE SDR WILL REMAIN OPEN FOR PART INFORMATION PENDING INVESTIGATION. *S/D* SHOP FINDINGS REVEALED A WORN T2 INNER AIRSEAL.