What was found
WHILE ON CLIMBOUT, "ALT DISAGREE" EICAS FLASHED MULTIPLE TIMES. TRIED CENTER ADC ON CAPT SIDE, MESSAGE CONTINUED TO INTERMITTENTLY OCCUR. EVENTUALLY RAN ALT DISAGREE (2 ADC'S REMAINING) CHECKLIST. ONCE THIS CHECKLIST WAS COMPLETED, DETERMINED THAT MOST LIKELY RH ADC FAILED AND L AND C ADC'S OKAY. RETURNED TO HKG WITHOUT MESSAGE RETURNING. ALSO DIFFERENCE BETWEEN ALTIMETERS WAS 300 FT LH TO RH, 200 FT CTR TO RH.(<P>FIM 34-12 TASK 864 AND 34-12 TASK 903 FOLLOWED. RH UPPER PITOT STATIC PROBE AND RH ADC REPLACED IAW AMM 34-11-01 AND 34-12-01. OPS TEST OF RH ADC AND RH UPPER PITOT STATIC PROBE HEAT TEST RESULT SATISFACTORY. LEAK CHECK OF PITOT STATIC SYSTEM, RESULT NORMAL. BOTH ALT AND AIRSPEED INDICATION ON L, R & CTR ADC CHECKED NORMAL. SN: 316987 & 97014873 / PN: 0856RE6 & 4040800-911</P>)