As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FOUND CENTER IRU FAULT LIGHT ON AFTER ALIGNMENT. GROUND SPEED WAS INCREASING BEYOND 500 MPH. INERTIAL REFERENCE UNIT FAULT. SWAPPED CENTER IRU WITH RIGHT IRU. PROBLEM FOLLOWED CENTER IRU. AC REDUCED TO CAT 1 & IRU DEFERRED. REPLACED BAD IRU. OP CHECK OK FOR SERVICE. SUSPECT FAULTY CIRCUIT.