Narrative:

The aircraft had not flown in some 8 weeks and had been in a maintenance shop where moisture had built up, unknown to me, in the pitot static system. While at FL290, elevator trim went to full down, the left side instruments iced over. They showed the aircraft maintaining level flight, the airspeed building slowly. A look at the right side after many seconds showed that the aircraft was in a descent and that the speed was not actually building since I had pulled off power and applied back pressure before I moved my lazy eyes to the right. We had lost some 800 ft and the autoplt would not release. As the autoplt would not disconnect with the go around button, it was necessary to pull the circuit breaker. It took both leg and arm power to hold aircraft from descending as the trim seemed to be frozen in the full down position. While at FL290, there were altitude excursions of under 1000 ft in both directions because the pressure would not release and the hand trim would not operate. I called ATC, told them what was happening, declared an emergency and descended to FL230. At FL230, the mechanical trim again operated and the emergency was basically over. The aircraft was landed at cha. We will remove the autoplt and the trim pitch servo and send out to be checked. The pitot system has been checked and is dry now.

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Original NASA ASRS Text

Title: A TURBO COMMANDER 690A IN CRUISE AT FL290 DECLARED AN EMER AND DSNDED DUE TO PITOT STATIC INST FAILURES CAUSED BY ICE IN TUBING.

Narrative: THE ACFT HAD NOT FLOWN IN SOME 8 WKS AND HAD BEEN IN A MAINT SHOP WHERE MOISTURE HAD BUILT UP, UNKNOWN TO ME, IN THE PITOT STATIC SYS. WHILE AT FL290, ELEVATOR TRIM WENT TO FULL DOWN, THE L SIDE INSTS ICED OVER. THEY SHOWED THE ACFT MAINTAINING LEVEL FLT, THE AIRSPD BUILDING SLOWLY. A LOOK AT THE R SIDE AFTER MANY SECONDS SHOWED THAT THE ACFT WAS IN A DSCNT AND THAT THE SPD WAS NOT ACTUALLY BUILDING SINCE I HAD PULLED OFF PWR AND APPLIED BACK PRESSURE BEFORE I MOVED MY LAZY EYES TO THE R. WE HAD LOST SOME 800 FT AND THE AUTOPLT WOULD NOT RELEASE. AS THE AUTOPLT WOULD NOT DISCONNECT WITH THE GAR BUTTON, IT WAS NECESSARY TO PULL THE CIRCUIT BREAKER. IT TOOK BOTH LEG AND ARM PWR TO HOLD ACFT FROM DSNDING AS THE TRIM SEEMED TO BE FROZEN IN THE FULL DOWN POS. WHILE AT FL290, THERE WERE ALT EXCURSIONS OF UNDER 1000 FT IN BOTH DIRECTIONS BECAUSE THE PRESSURE WOULD NOT RELEASE AND THE HAND TRIM WOULD NOT OPERATE. I CALLED ATC, TOLD THEM WHAT WAS HAPPENING, DECLARED AN EMER AND DSNDED TO FL230. AT FL230, THE MECHANICAL TRIM AGAIN OPERATED AND THE EMER WAS BASICALLY OVER. THE ACFT WAS LANDED AT CHA. WE WILL REMOVE THE AUTOPLT AND THE TRIM PITCH SERVO AND SEND OUT TO BE CHKED. THE PITOT SYS HAS BEEN CHKED AND IS DRY NOW.

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