As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LAS - FLT 2976 - AIR TURN BACK, AT CLIMB POWER FL 200 NR 1 ENGINE COMMENCED SEVERE VIBRATIONS. ALL ENGINE INDICATIONS NORMAL. RETARDED THRUST LEVER. VIBRATIONS CONTINUED. SHUTDOWN ENGINE IAW QRH. RETURNED LAS. FOUND TURBINE WHEEL BLADES MISSING MATERIAL. REMOVED AND REPLACED NR 1 ENGINE. TEARDOWN FOUND NR 1 HIGH PRESSURE TURBINE BLADE FAILED DUE TO AN INTERNAL CASTING DEFECT KNOWN AS A COLD SHUT. (M)