Narrative:

10,000 MSL was the requested cruise altitude for this flight. A 1000' callout by the non flying pilot was made leaving 9000' for 10,000' and verified by the flying pilot. A call and subsequent confirmation was noted reaching 10,000'. The flying pilot's instruments were stabilized and the cruise checks were performed and sterile cockpit procedures were no longer in effect. A minute or so later we were switched from one center frequency to the following sector. Upon checking in 'level at one zero thousand' the center replied with 'roger' and an altimeter setting slightly higher (about .09' hg) than what was already set in. Both pilots dialed in the new altimeter setting and two things occurred. One, the flying pilot's altimeter did not budge and stayed at 10,000'. Two, the non flying pilot's altimeter jumped from 10,000' to 11,200'. Immediately we asked for a mode C verification from center to which they showed us at 10,000'. The encoder was on the flying pilot's side. We switched encoders and center replied 11,200'. We were unsure which was correct and requested 8000'. We were in VMC conditions, marginal, but VMC. Leaving what we were sure was 10,000 both altimeters responded within appropriate limits of each other with the flying pilot's altimeter now responding to the higher altimeter setting. Both encoders responded appropriately also below 10,000. Maintenance was told to clear flying pilot's altitude and check the whole system. Probable cause of situation was deicing crew's possibly getting deicing fluid in the static system. No way to actually know. I feel that since both altimeters stuck, that was probably the cause. I'm not sure if we actually busted an assigned altitude since at 10,000' and above, at that time, both systems seemed suspect. Corrective action I feel is better vigilance from deicing crews. All pitot static heat systems were indicating normal.

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Original NASA ASRS Text

Title: LTT TYPE ACFT HAD ERRONEOUS ALTIMETER READING AT 10,000'. SWITCHED STATIC AIR SOURCE. HAD CHANGE IN ALTIMETER READING.

Narrative: 10,000 MSL WAS THE REQUESTED CRUISE ALT FOR THIS FLT. A 1000' CALLOUT BY THE NON FLYING PLT WAS MADE LEAVING 9000' FOR 10,000' AND VERIFIED BY THE FLYING PLT. A CALL AND SUBSEQUENT CONFIRMATION WAS NOTED REACHING 10,000'. THE FLYING PLT'S INSTRUMENTS WERE STABILIZED AND THE CRUISE CHECKS WERE PERFORMED AND STERILE COCKPIT PROCS WERE NO LONGER IN EFFECT. A MINUTE OR SO LATER WE WERE SWITCHED FROM ONE CENTER FREQ TO THE FOLLOWING SECTOR. UPON CHECKING IN 'LEVEL AT ONE ZERO THOUSAND' THE CENTER REPLIED WITH 'ROGER' AND AN ALTIMETER SETTING SLIGHTLY HIGHER (ABOUT .09' HG) THAN WHAT WAS ALREADY SET IN. BOTH PLTS DIALED IN THE NEW ALTIMETER SETTING AND TWO THINGS OCCURRED. ONE, THE FLYING PLT'S ALTIMETER DID NOT BUDGE AND STAYED AT 10,000'. TWO, THE NON FLYING PLT'S ALTIMETER JUMPED FROM 10,000' TO 11,200'. IMMEDIATELY WE ASKED FOR A MODE C VERIFICATION FROM CENTER TO WHICH THEY SHOWED US AT 10,000'. THE ENCODER WAS ON THE FLYING PLT'S SIDE. WE SWITCHED ENCODERS AND CENTER REPLIED 11,200'. WE WERE UNSURE WHICH WAS CORRECT AND REQUESTED 8000'. WE WERE IN VMC CONDITIONS, MARGINAL, BUT VMC. LEAVING WHAT WE WERE SURE WAS 10,000 BOTH ALTIMETERS RESPONDED WITHIN APPROPRIATE LIMITS OF EACH OTHER WITH THE FLYING PLT'S ALTIMETER NOW RESPONDING TO THE HIGHER ALTIMETER SETTING. BOTH ENCODERS RESPONDED APPROPRIATELY ALSO BELOW 10,000. MAINT WAS TOLD TO CLEAR FLYING PLT'S ALT AND CHECK THE WHOLE SYSTEM. PROBABLE CAUSE OF SITUATION WAS DEICING CREW'S POSSIBLY GETTING DEICING FLUID IN THE STATIC SYSTEM. NO WAY TO ACTUALLY KNOW. I FEEL THAT SINCE BOTH ALTIMETERS STUCK, THAT WAS PROBABLY THE CAUSE. I'M NOT SURE IF WE ACTUALLY BUSTED AN ASSIGNED ALT SINCE AT 10,000' AND ABOVE, AT THAT TIME, BOTH SYSTEMS SEEMED SUSPECT. CORRECTIVE ACTION I FEEL IS BETTER VIGILANCE FROM DEICING CREWS. ALL PITOT STATIC HEAT SYSTEMS WERE INDICATING NORMAL.

Data retrieved from NASA's ASRS site as of August 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.