CRP LTT CLIMBED ABOVE ASSIGNED ALT.

Narrative

GSO APCH CLRED US TO 10000' AND ON COURSE AND I IMMEDIATELY CLBED TO AND LEVELED AT 10000'. A SHORT PERIOD OF TIME ELAPSED AND THEN THE DEP CTLR CALLED AND SAID HE WANTED US ON UP TO 10000' AND THAT HE SHOWED US ABOUT 6000' AND DSNDING. MY COPLT THEN DREW MY ATTN TO THE COPLT'S INSTRUMENTS WHICH INDICATED THAT WE WERE DSNDING OUT OF 6000'. MY COPLT TOLD THE CTLR WE HAD CONFLICTING ALTIMETER READINGS WITH ONE SHOWING LEVEL AT 10000' AND THE OTHER SHOWING JUST UNDER 6000'; DSNDING SLIGHTLY. HE CONFIRMED SEEING US DSNDING OUT OF 6000'. THEN; BECAUSE OF THE URGING OF THE CTLR THAT WE WERE DSNDING; AND THE CONFUSION OF THE MOMENT; I BEGAN ANOTHER CLB; CONVINCED THE CTLR WAS CONFIRMING THAT I WAS BELOW 10000'. DURING THIS CLB; WHICH WAS IN EXCESS OF 3000 FPM; I TRIED TO DETERMINE WHAT THE PROB WAS. I THEN SAW THE COPLT'S AIRSPD INDICATOR READING 0 AND THE COPLT'S VVI READING ABOUT A 400 FPM CLB. TOTAL CONFUSION NOW EXISTED. DURING THIS SAME TIME; THE GSO CTLR HANDED US OFF TO ZDC. WHEN THE CENTER CTLR TOOK THE HDOF; I TOLD HIM THAT I HAD A SEVERE ALTIMETER PROB AND WASN'T SURE HOW HIGH I WAS. I THEN USED THE CABIN ALTIMETER AND DIFFERENTIAL PRESSURE GAUGE AS ANOTHER SOURCE TO DETERMINE OUR ALT. THESE INSTRUMENTS IMMEDIATELY TOLD ME THAT MY PROB WAS IN THE COPLT'S INSTRUMENTS. I THEN PUT MY FAITH BACK INTO THE PLT'S INSTRUMENTS; WHICH INDICATED WE WERE RAPIDLY CLBING OUT OF 17000'. I STOPPED THE CLB AND TOLD THE CENTER CTLR THAT I THOUGHT I WAS ABOVE 17000'; BUT WASN'T SURE. WE DECIDED TO CANCEL IFR AND CONTINUE VFR; AND CONTINUED W/O FURTHER INCIDENT. MAINT PROB: COPLT'S ALTIMETER HAD DEVELOPED A LARGE STATIC LEAK. THE #2 ENCODER WAS IN OPERATION WHEN THIS OCCURRED.