As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) ACFT ELECTED TO DO AN AIR TURNBACK DUE TO THE AVAILABILITY OF MAINTENANCE AT DESTINATION. THE ACFT EXPERIENCED AN IRS MESSAGE IN FLT VERIFY POSITION IRS. ACFT RETURNED. MAINTENANCE REPLACED THE LT ADIRU. SYSTEM WAS TESTED SERVICEABLE IAW AMM 34-21-01.