What was found
AT CRUISE (FL280) AMBER "ALT" FLAG APPEARED ON BOTH ALTIMETERS. FO WAS PILOT FLYING AND SRC WAS ON FO SIDE. IN FLIGHT DATA AS FOLLOWS: ADS1 - 28220', ADS2 - 28000', ADS3 - 28080' ALTIMETER 29.92, T=56 C, IESS - 28070. XPDR#1 WAS IN USE. NO CHANGE WHEN SELECTING XPDR#2. UPON DESCENT "ALT" FLAG EXTINGUISHED AND REMAINED SO FOR DURATION OF RETURN FLIGHT AT FL250, APPROACH AND LANDING. PERFORMED ALTITUDE SPLIT EVALUATION REF FIM 34-15-00-810-850-A ADSP 1 SHOWS 100% RESPONSIBLE PERFORMED GVI OF ADS PROBES, NO DEFECTS NOTED. I HAVE PERFORMED ALL INSPECTIONS AND/OR TESTS AS DETAILED IN PARAGRAPH C OF THIS FERRY PERMIT, AND HAVE DETERMINED THAT THE AIRCRAFT IS SAFE FOR FERRY FLIGHT FROM ANC TO PDX. REPLACED THE #1 AIR DATA PROBE.