As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER T/O 1 IRU FAILED, 2 IRU WAS ALREADY MEL'D INOP. RETURN TO DFW. REMOVED AND REPLACED THE 1 IRU PER MM 34-25-00 -05-1, PERFORMED IRS SYS ADJ/TEST IN CONJUNCTION WITH WRI 34-43-6941 (IRU 3) AND WRI 34-43-6937 (IRU 2). ALL IRU'S TESTED NORMAL. PERFORMED AFS/LAND TEST, TEST PASSED. A/C CAT STATUS PLACED INTO A/C CAT II; AP1 & 2 CK CAT III.