Narrative:

We experienced a complete pitot static failure. During the descent from FL430 to FL350 both altimeters and airspeed indicators and the standby systems began to show erroneous readings. As we tried to diagnose the problem and determine which if any systems were accurate. ATC noticed that we had slowed our descent. We told them that we were not sure of our altitude and that we were somewhere in the '30's.' ATC then modified our clearance to stop at FL360 instead of FL350. At this point we were still fairly confident that my altimeter was accurate; however as we tried to descend we then realized that my altimeter; which we thought was correct; was indeed faulty. Our altitude was FL315 when we finally determined my altimeter was inaccurate. We then immediately stopped the descent and leveled off. As soon as we determined my altimeter was wrong we declared an emergency as we did not have any accurate idea of what our altitude was. ATC had turned us to the northwest throughout the whole time we were unsure of our altitude. As soon as we declared an emergency; ATC cleared us direct to ZZZ. As we descended further we felt fairly confident that we had a correct altimeter reading and since ZZZ was VMC we felt we could cancel the emergency. We then proceeded to the airport where we landed without incident. Callback conversation with reporter revealed the following information: not only were the altimeters unreliable but airspeed indications were also erratic and anomalous over-speed warnings were generated. ATC turned the aircraft away from traffic so there were no conflicts although the altitude readout from the transponder may have been off by several thousand feet. Once they got to a lower altitude the pitot static instruments came into agreement and we were able to continue to destination and land visually. Maintenance discovered that water had gotten into the pitot static system causing it to read incorrectly. Water may have entered through a static port while the aircraft was parked over night in a rain storm although pitot covers were installed and the aircraft spent the last night before departure in a hanger. This failure indicates that all three pitot static systems are interconnected in some way; which is troubling. Although the reporter was very new to this aircraft the first officer was very experienced.

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Original NASA ASRS Text

Title: LEAR31 CAPTAIN REPORTS PITOT STATIC SYSTEM FAILURE DURING DESCENT RESULTING IN DESCENT BELOW ASSIGNED ALTITUDE. THE CREW DECLARED AN EMERGENCY; AND AN UNEVENTFUL APPROACH AND LANDING ENSUED.

Narrative: WE EXPERIENCED A COMPLETE PITOT STATIC FAILURE. DURING THE DESCENT FROM FL430 TO FL350 BOTH ALTIMETERS AND AIRSPEED INDICATORS AND THE STANDBY SYSTEMS BEGAN TO SHOW ERRONEOUS READINGS. AS WE TRIED TO DIAGNOSE THE PROBLEM AND DETERMINE WHICH IF ANY SYSTEMS WERE ACCURATE. ATC NOTICED THAT WE HAD SLOWED OUR DESCENT. WE TOLD THEM THAT WE WERE NOT SURE OF OUR ALTITUDE AND THAT WE WERE SOMEWHERE IN THE '30'S.' ATC THEN MODIFIED OUR CLEARANCE TO STOP AT FL360 INSTEAD OF FL350. AT THIS POINT WE WERE STILL FAIRLY CONFIDENT THAT MY ALTIMETER WAS ACCURATE; HOWEVER AS WE TRIED TO DESCEND WE THEN REALIZED THAT MY ALTIMETER; WHICH WE THOUGHT WAS CORRECT; WAS INDEED FAULTY. OUR ALTITUDE WAS FL315 WHEN WE FINALLY DETERMINED MY ALTIMETER WAS INACCURATE. WE THEN IMMEDIATELY STOPPED THE DESCENT AND LEVELED OFF. AS SOON AS WE DETERMINED MY ALTIMETER WAS WRONG WE DECLARED AN EMERGENCY AS WE DID NOT HAVE ANY ACCURATE IDEA OF WHAT OUR ALTITUDE WAS. ATC HAD TURNED US TO THE NORTHWEST THROUGHOUT THE WHOLE TIME WE WERE UNSURE OF OUR ALTITUDE. AS SOON AS WE DECLARED AN EMERGENCY; ATC CLEARED US DIRECT TO ZZZ. AS WE DESCENDED FURTHER WE FELT FAIRLY CONFIDENT THAT WE HAD A CORRECT ALTIMETER READING AND SINCE ZZZ WAS VMC WE FELT WE COULD CANCEL THE EMERGENCY. WE THEN PROCEEDED TO THE AIRPORT WHERE WE LANDED WITHOUT INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: NOT ONLY WERE THE ALTIMETERS UNRELIABLE BUT AIRSPEED INDICATIONS WERE ALSO ERRATIC AND ANOMALOUS OVER-SPEED WARNINGS WERE GENERATED. ATC TURNED THE ACFT AWAY FROM TRAFFIC SO THERE WERE NO CONFLICTS ALTHOUGH THE ALTITUDE READOUT FROM THE TRANSPONDER MAY HAVE BEEN OFF BY SEVERAL THOUSAND FEET. ONCE THEY GOT TO A LOWER ALTITUDE THE PITOT STATIC INSTRUMENTS CAME INTO AGREEMENT AND WE WERE ABLE TO CONTINUE TO DESTINATION AND LAND VISUALLY. MAINTENANCE DISCOVERED THAT WATER HAD GOTTEN INTO THE PITOT STATIC SYSTEM CAUSING IT TO READ INCORRECTLY. WATER MAY HAVE ENTERED THROUGH A STATIC PORT WHILE THE AIRCRAFT WAS PARKED OVER NIGHT IN A RAIN STORM ALTHOUGH PITOT COVERS WERE INSTALLED AND THE AIRCRAFT SPENT THE LAST NIGHT BEFORE DEPARTURE IN A HANGER. THIS FAILURE INDICATES THAT ALL THREE PITOT STATIC SYSTEMS ARE INTERCONNECTED IN SOME WAY; WHICH IS TROUBLING. ALTHOUGH THE REPORTER WAS VERY NEW TO THIS AIRCRAFT THE FIRST OFFICER WAS VERY EXPERIENCED.

Data retrieved from NASA's ASRS site as of May 2009 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.