What was found
SHIP 1817 -MISC/DE- DUE TO IAS DISAGREE MESSAGE. CAPTAIN'S AIRSPEED UNRELIABLE. CAPT'S AIRSPEED FOLLOWED ALTITUDE CHANGE FINISHED QRH WITH CAPT ON R AIR DATA STAY OUTSIDE RVSM AIRSPACE ALT F340 MACH .80 SPEED CAPT STARTED TO DECLINE DESCEND TO F300 CAPT A/S DECREASE 40 KTS COMPARED TO F/O IN THE DESCENT F/O AND STANDBY A/S MATCHED AT ALL TIMES CORRECTIVE ACTION: FAULT CODE 34-21050 (L ADIRU) RECORDED. REPLACED LEFT ADIRU AND CAPTAIN'S PITOT ADM. OPS CHECKS GOOD. (LP 4714886)