What was found
(CAN) PILOT NOTED ON MULTIPLE OCCASIONS THE HEADING MISCOMPARE FLAG IN VIEW. IN CRUISE HEADING WOULD DRIFT ON THE CO-PILOTS PFD UP TO 14 DEGREES AND DRIFT BACK. WHEN COMPARING HEADINGS WITH THE STAND ALONE SAND INSTRUMENT, THE NR 1 SIDE, PILOT PFD, DID NOT DRIFT. AT BASE, A GROUND RUN WAS PERFORMED, WHILE STATIC, ENGINE RUNNING, 2 PFD HEADING WAS OBSERVED DRIFTING AFTER 5-6 MINUTES. THE NR 2 PFD WAS ALSO NOTED TO EVENTUALLY DISPLAY A 2 DEGREES LT BANK AND A 2 DEGREES NOSE DOWN ATTITUDE. ADAHRS ASSY REPLACED. ON A SUBSEQUENT POWER CYCLE, AHRS NR 2 FAIL CAS MESSAGE WAS IN VIEW.