ACFT EQUIP PROB. FLC DETECTS THAT THEY ARE RECEIVING ERRONEOUS DATA FROM THE AIR DATA COMPUTERS AND THE PERFORMANCE MGMNT SYS. OVERWATER OP.

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POSSIBLE CAUSE WAS A FAULTY INPUT FROM CADC #2 TO PMS; WHICH WAS COMMANDING AUTOTHROTTLES AND AUTOPLT. ON B-747 ACFT; ABNORMAL PROCS SHOULD WARN CREWS OF THE NEED TO DISENGAGE PMS AND AUTOTHROTTLES DURING PITOT STATIC SYS LOSS; BECAUSE ERRONEOUS SIGNALS ARE INPUT TO CADC #2 WHICH SENDS TRUE AIRSPD SIGNALS TO PMS. MALFUNCTION: FAILURE OF PITOT STATIC SYS; BOTH CAPT'S AND FO'S. DESCRIPTION: I WAS AT THE GALLEY FIXING A MEAL WHEN THE FE CALLED ME BACK TO THE COCKPIT SAYING THERE WAS A PROB WITH THE AIRSPD INDICATORS. I QUICKLY SCANNED THE FLT INSTS AND POINTED OUT THAT THE PITCH ATTITUDE ON BOTH ATTITUDE DIRECTOR INDICATORS CORRESPONDED TO NORMAL CRUISE PITCH; APPROX 2.6 DEGS ACFT NOSE UP. AT THIS TIME; THE CAPT'S MACH AIRSPD INDICATOR SHOWED ABOUT 20 KTS LOWER THAN FO'S; WHICH WAS INDICATING 262 KTS/.839 MACH. I XCHKED THE PMS PERFORMANCE PAGE AND INS GND SPD; WHICH CORRELATED WITH THE FO'S AIRSPD INDICATOR. AT THE SAME TIME I ASKED THE FE TO TAKE OUT THE ACFT OP MANUAL SO WE COULD REVIEW THE ABNORMAL PROCS. AFTER REVIEWING THE ABNORMAL AND SUPPLEMENTAL PROCS; AND CHKING PITOT HEAT CIRCUIT BREAKERS AND LIGHTS; AND INST AND CADC CIRCUIT BREAKERS; AS WELL AS CONSULTING WITH OUR FLT MECH; WE CONCLUDED THAT WE MIGHT HAVE PITOT BLOCKAGE DUE TO INEFFECTIVE PITOT HEAT OR BLOCKED DRAIN HOLES. SINCE THE FO'S AIRSPD CORRESPONDED WITH CHARTED DATA AND PMS; WE ELECTED TO SWITCH FROM AUTOPLT A TO AUTOPLT B AND RE- ENGAGE THE PMS WHICH WE HAD DISCONNECTED AT THE BEGINNING OF THE PROB. AFTER CONCLUDING THE ABNORMAL PROCS; I ASKED THE FO HOW OUR FLT PLAN FUEL AND TIME SCORE LOOKED AND HE REPLIED FUEL IS PLUS 6000 LBS AND WE HAD FALLEN BEHIND 8 MINS ON THE FLT PLAN. THE FO SUGGESTED WE MUST HAVE ENCOUNTERED AN INCREASE IN HEADWIND. I SAID THAT CAN'T BE RIGHT AND TOOK THE FLT PLAN AND PROCEEDED TO CHK THE MATH AS WELL AS INS GND SPD AND WIND AGAINST THE FLT PLAN. DURING THIS TIME I CONTINUED TO SCAN THE FLT INSTS. FO'S AIRSPD INDICATOR STILL SHOWED OUR CHARTED 262 KTS/.84 MACH WITH ADI AT 2.6 AND PMS ENGAGED. WHILE CHKING THE FLT PLAN AGAINST THE INS GND SPD AND WIND; I FOUND THAT THE GND SPD WAS DOWN TO 358 KTS; WIND COMPONENT WAS ONLY 10 KTS OVER FLT PLAN. I MADE A COMMENT TO THE CREW THAT SOMETHING IS TERRIBLY WRONG HERE. I LOOKED AT CAPT'S AND FO'S ADI AND BOTH HAD GONE UP TO 6.5 DEGS. AT APPROX XA05Z; AND IN MODERATE TURB; I TOLD THE FO TO ASK GANDER TO LET US DSND TO FL370-FL350 TO GET TO A WARMER TEMP. HE TRIED SEVERAL TIMES TO COMMUNICATE OUR PROB TO GANDER BUT WAS CONTINUALLY COVERED BY SEVERAL OTHER ACFT XMITTING ON THE FREQ. AT THIS TIME THE ACFT CONTINUED TO PITCH UP; AUTOPLT B WAS THEN DISENGAGED AND MAX PWR APPLIED AS I COULD FEEL AN IMPENDING STALL. I INSTRUCTED THE FO TO DECLARE AN EMER AND STARTED A SHALLOW TURN TO THE S TO CLR THE TRACK WHILE COMMENCING A DSCNT. PASSING FL380 THE CAPT'S AIRSPD INDICATOR SUDDENLY INCREASED TO NEAR NORMAL WHILE THE FO'S AIRSPD AND ALTIMETER INDICATORS BECAME ERRATIC. AT THIS TIME; GANDER INFORMED US OF TFC OPPOSITE DIRECTION AT FL330; FL350; AND FL370. I CONTINUED MY TURN S TO CLR THE TRACK AND TFC. SINCE INDICATIONS APPEARED NORMAL ON CAPT'S AIRSPD AND ALTIMETER; AT APPROX 8-9 MI S OF TRACK; I DECIDED TO CLB BACK TO FL390 AND THEN RETURN TO THE TRACK; WHILE INFORMING GANDER. THE LOWEST LEVEL ATTAINED DURING DSCNT WAS FL375. ONCE BACK AT FL390; THE CAPT'S INDICATIONS WERE NORMAL WHILE THE FO'S AIRSPD AND ALTIMETER INDICATED MACH 1 PLUS AND 650 FT HIGHER THAN CAPT'S; RESPECTIVELY. SUBSEQUENTLY; DURING THE REMAINDER OF THE FLT; THE PMS FAILED; AND DURING DSCNT TO JFK; THE FO'S AIRSPD INDICATOR WENT TO '0.' WE WENT ON TO MAKE AN UNEVENTFUL LNDG AT JFK USING ILS AND INS GND SPD AS BACKUP. NOTE 1: DURING COMPLETION OF ABNORMAL PROCS; THE ALTERNATE STATIC SOURCES WERE TRIED ON BOTH SIDES AND HAD NO EFFECT ON AIRSPD INDICATIONS. NOTE 2: AFTER PMS FAILED; THE REMAINING WAYPOINTS WERE INSERTED INTO ALL 3 INS'S MANUALLY.