AN AEROSTAR 602P IN CRUISE AT 15000 FT HAS THE AUTOPLT COMMAND A PITCH UP AND WAS UNABLE TO DISCONNECT AUTOPLT WITH YOKE SWITCH. CONSOLE SWITCH OK. ELECTRIC STABILIZER TRIM ALSO INOP.

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IFR FLT FROM OCF TO ILG; 15000 FT. APPROX 30 NM N OF FAY ON COURSE DIRECT RIC; THE AUTOPLT EXPERIENCED AN UNCOMMANDED PITCH UP. ATTEMPT TO DISCONNECT AUTOPLT VIA YOKE MOUNTED TRIM SWITCH WAS UNSUCCESSFUL. DISCONNECT WAS OBTAINED BY USING THE CONSOLE MOUNTED AUTOPLT SWITCH. THIS OCCURRED AT APPROX FL180. HOWEVER; THE ELECTRIC TRIM FAILED TO OPERATE (THIS ACFT HAS NO MANUAL TRIM). WITH THE ACFT SERIOUSLY OUT OF PITCH TRIM; IT WAS DIFFICULT TO CTL. ZDC CTLR DIRECTED US TO RDU WHERE THE APCH CTLR ASSISTED US WITH VECTORS TO A VISUAL APCH TO RWY 5L. CONDITIONS AT RDU WERE BASES 2400 FT MSL. WE OBTAINED MAINT ASSISTANCE AT RDU; EXACT CAUSE NOT DETERMINED. AUTOPLT WAS DISABLED AND ELECTRIC TRIM RE-ESTABLISHED. THE NEXT DAY (MAR/TUE/04) WE FILED IFR FOR RDU DIRECT ILG WITHOUT THE AUTOPLT. THIS INCIDENT WAS IN IMC. AT ONE POINT; THE ACFT DEVELOPED A FULL STALL; RECOVERY REQUIRED ABOUT 4000 FT. I HAVE FLOWN THIS TYPE ACFT FOR 12 YRS AND HAVE TAKEN RECURRENT TRAINING EVERY 12 MONTHS DURING THAT PERIOD. WITHOUT THIS TRAINING; I DOUBT THE OUTCOME WOULD HAVE BEEN THE SAME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED NOT ONLY DID THE AUTOPLT FAIL; BUT THE ELECTRIC TRIM WAS INOP AND THIS IS A PROB WITH THIS AIRPLANE AS IT HAS NO MANUAL ELEVATOR TRIM. THE RPTR SAID ON THE GND THE AUTOPLT COMPUTER AND SERVOS OPERATED NORMALLY BUT THE COMPUTER WAS SENT TO A REPAIR FACILITY FOR A COMPLETE TEST. THE RPTR STATED THE TESTING HAS NOT BEEN COMPLETED AND HAS RECEIVED NO STATUS ON THE COMPUTER. THE RPTR SAID NO EMER WAS DECLARED AS THE RPTR WANTED TO 'WORK OUT THE PROB FOR HIMSELF.'