Narrative:

I had descended from FL270 to FL210. I lost the #2 GPS then about 34 mins later I had an airspeed disagreement warning. Shortly after this; the autoplt disengaged and the aircraft pitched up. I pressed the autoplt disconnect button and corrected the attitude and altitude. At the time of the transient I had several things going on. Altitude change/leveloff. Multiple malfunctions and the pitch change. It was controled quickly but an altitude transient did occur. Before takeoff we had an 'avionics data bus' failure 3 times. I called maintenance and uploaded the computer history. They advised us to start engines 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 system but I am only aware of uncommanded communication frequency changes. I can't help but think that these problems 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 altitude transient although I noticed it right away and made the correction. As I was making the correction; ATC asked us about the altitude and I responded. Callback conversation with reporter revealed the following information: reporter advised that the problem was traced to water in the pitot/static/air data system that froze at altitude.

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Original NASA ASRS Text

Title: 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.

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.