As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: PILOT REPORTS ON DESCENT, FMC MESSAGE- IR5-L DRIFT THEN VERIFY POSITION LEFT PFD TUMBLED AND HEADING WAS INCORRECT. FINALLY THE LEFT IRS FAULT LIGHT ILLUMINATED. ON FINAL AIRSPEED LOW WARNINGS. THE F/O INSTRUMENTS WERE NORMAL THROUGHOUT. MAINTENANCE REMOVED AND REPLACED LEFT AIR DATA INERTIAL REFERENCE UNIT IAW AMM 34-21-01 . OPS CHECKS GOOD.