As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT 3541, BOTH VPU QUIT COMMUNICATING INFLIGHT. IRS'S ALSO STARTED TO DRIFT SEVERELY. LT NAV FLIGHT PLAN ON ND WAS ALSO SHOWING SEVER DEVIATION FROM COURSE. NO INDICATIONS OF BAD IR'S WERE GIVEN. AIR RETURN TO MSP. MAINTENANCE RELOADED GNS-X NAV DATABASES. NR 1 AND NR 2 GNS-X CHECK GOOD IAW AVRO MM CHAP 34.