As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE OPERATION CAPTAIN’S RMI CARD AND FO`S HSI CARD STOPPED TURNING IN FLIGHT, BOTH RMI NEEDLES FROZE IN POSITION. AC RETURNED TO DEPARTURE WHERE IT LANDED WITHOUT INCIDENT. POST FLIGHT INSPECTION REVEALED THE FLIGHT INSTRUMENT ACCY UNIT AT FAULT. REMOVED AND REPLACED FLIGHT INSTRUMENT ACCY UNIT, OPS CHECK GOOD. NO OTHER DEFECTS WERE NOTED. AIRCRAFT WAS RETURNED TO SERVICE. (K)