As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT 2767, ALTITUDE AND HEADING RED FLAGGED ON F/O'S SIDE. USED X-SIDE DATA AS PER QRH. AIR RETURN TO SUX. MAINTENANCE INSPECTED AC AND FOUND SAFE FOR ONE TIME FERRY FLIGHT FROM SUX TO MSP FOR INTERMITTANT F/O'S AHARS. MSP MAINTENANCE REMOVED AND REPLACED NR 2 AHRS COMPUTER PN 622-6190-113 SN/ON 2950 SN/OFF 2940, NR 2 AHRS OPS CHECKS GOOD IAW SF340MM CHAP 34.