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

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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.