EA50 EXPERIENCE ALT DEV WHEN AUTOPLT MALFUNCTIONS DURING TROUBLESHOOTING OF NAV AND PITOT SYSTEM FAULTS.

Narrative

I HAD DSNDED FROM FL270 TO FL210. I LOST THE #2 GPS THEN ABOUT 34 MINS LATER I HAD AN AIRSPD DISAGREEMENT WARNING. SHORTLY AFTER THIS; THE AUTOPLT DISENGAGED AND THE ACFT PITCHED UP. I PRESSED THE AUTOPLT DISCONNECT BUTTON AND CORRECTED THE ATTITUDE AND ALT. AT THE TIME OF THE TRANSIENT I HAD SEVERAL THINGS GOING ON. ALT CHANGE/LEVELOFF. MULTIPLE MALFUNCTIONS AND THE PITCH CHANGE. IT WAS CTLED QUICKLY BUT AN ALT TRANSIENT DID OCCUR. BEFORE TKOF WE HAD AN 'AVIONICS DATA BUS' FAILURE 3 TIMES. I CALLED MAINT AND UPLOADED THE COMPUTER HISTORY. THEY ADVISED US TO START ENGS AGAIN AND SEE IF THE MALFUNCTION WAS PRESENT AGAIN. THEY SAID THAT IF ALL WAS NORMAL THIS TIME WE COULD FLY. THERE IS SOME HISTORY OF COMPUTER/AVIONICS MALFUNCTIONS IN THE SYS BUT I AM ONLY AWARE OF UNCOMMANDED COM FREQ CHANGES. I CAN'T HELP BUT THINK THAT THESE PROBS MIGHT BE RELATED AND I KNOW THAT ECLIPSE IS WORKING ON IT. THEORETICALLY; IF I HAD KNOWN THAT THIS MALFUNCTION WAS COMING; IT MIGHT HAVE BEEN POSSIBLE TO REDUCE THE AMOUNT OF THE ALT TRANSIENT ALTHOUGH I NOTICED IT RIGHT AWAY AND MADE THE CORRECTION. AS I WAS MAKING THE CORRECTION; ATC ASKED US ABOUT THE ALT AND I RESPONDED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER ADVISED THAT THE PROBLEM WAS TRACED TO WATER IN THE PITOT/STATIC/AIR DATA SYSTEM THAT FROZE AT ALTITUDE.