As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INERTIAL REFERENCE SYSTEM DRIFT OR FLIGHT MANAGEMENT COMPUTER NAV PROBLEM IN FLIGHT. *S/D* BOTH NR 1 AND NR 2 INERTIAL REFERENCE UNITS (NAV UNITS) WERE REPLACED PRECAUTIONARY. SYSTEM OPERATION HAS SINCE BEEN NORMAL. THE SHOP REPORTED THEY WERE UNABLE TO FIND ANY FAULT IN THE REPLACED IRU'S, TESTED NORMAL.