Narrative:

Possible cause was a faulty input from CADC #2 to pms, which was commanding autothrottles and autoplt. On B-747 aircraft, abnormal procedures should warn crews of the need to disengage pms and autothrottles during pitot static system loss, because erroneous signals are input to CADC #2 which sends true airspeed signals to pms. Malfunction: failure of pitot static system, both captain's and first officer's. Description: I was at the galley fixing a meal when the flight engineer called me back to the cockpit saying there was a problem with the airspeed indicators. I quickly scanned the flight instruments and pointed out that the pitch attitude on both attitude director indicators corresponded to normal cruise pitch, approximately 2.6 degrees aircraft nose up. At this time, the captain's mach airspeed indicator showed about 20 KTS lower than first officer's, which was indicating 262 KTS/.839 mach. I crosschecked the pms performance page and INS ground speed, which correlated with the first officer's airspeed indicator. At the same time I asked the flight engineer to take out the aircraft operation manual so we could review the abnormal procedures. After reviewing the abnormal and supplemental procedures, and checking pitot heat circuit breakers and lights, and instrument and CADC circuit breakers, as well as consulting with our flight mechanic, we concluded that we might have pitot blockage due to ineffective pitot heat or blocked drain holes. Since the first officer's airspeed 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 problem. After concluding the abnormal procedures, I asked the first officer how our flight plan fuel and time score looked and he replied fuel is plus 6000 pounds and we had fallen behind 8 mins on the flight plan. The first officer suggested we must have encountered an increase in headwind. I said that can't be right and took the flight plan and proceeded to check the math as well as INS ground speed and wind against the flight plan. During this time I continued to scan the flight instruments. First officer's airspeed indicator still showed our charted 262 KTS/.84 mach with ADI at 2.6 and pms engaged. While checking the flight plan against the INS ground speed and wind, I found that the ground speed was down to 358 KTS, wind component was only 10 KTS over flight plan. I made a comment to the crew that something is terribly wrong here. I looked at captain's and first officer's ADI and both had gone up to 6.5 degrees. At approximately XA05Z, and in moderate turbulence, I told the first officer to ask gander to let us descend to FL370-FL350 to get to a warmer temperature. He tried several times to communicate our problem to gander but was continually covered by several other aircraft transmitting on the frequency. At this time the aircraft continued to pitch up, autoplt B was then disengaged and maximum power applied as I could feel an impending stall. I instructed the first officer to declare an emergency and started a shallow turn to the south to clear the track while commencing a descent. Passing FL380 the captain's airspeed indicator suddenly increased to near normal while the first officer's airspeed and altimeter indicators became erratic. At this time, gander informed us of traffic opposite direction at FL330, FL350, and FL370. I continued my turn south to clear the track and traffic. Since indications appeared normal on captain's airspeed and altimeter, at approximately 8-9 mi south of track, I decided to climb back to FL390 and then return to the track, while informing gander. The lowest level attained during descent was FL375. Once back at FL390, the captain's indications were normal while the first officer's airspeed and altimeter indicated mach 1 plus and 650 ft higher than captain's, respectively. Subsequently, during the remainder of the flight, the pms failed, and during descent to jfk, the first officer's airspeed indicator went to '0.' we went on to make an uneventful landing at jfk using ILS and INS ground speed as backup. Note 1: during completion of abnormal procedures, the alternate static sources were tried on both sides and had no effect on airspeed indications. Note 2: after pms failed, the remaining waypoints were inserted into all 3 INS's manually.

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Original NASA ASRS Text

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

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.