LTT FLC CLRED TO DSND; BUT ACFT BEGINS A SUBTLE CLB DUE TO APPARENT SELECTION OF WRONG BUTTON ON MCP. ALTDEV. IMPROPER MODE CTL PANEL USE.

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OPERATING CVG TO ROA; APPROX 80 MI W OF ROA. CTLR CLRED US FOR PLT'S DISCRETION DSCNT FROM FL220 DOWN TO 13000 FT OR 15000 FT (CAN'T REMEMBER WHICH). I RESET ALT WINDOW AND PUSHED 'DSC' (DSCNT) BUTTON; NOTED ALT ARMED ILLUMINATED FOLLOWED BY SLIGHT PITCHOVER. AFTER A FEW SECONDS; WITH ABOUT 1500 FPM RATE ESTABLISHED; I AGAIN PUSHED DSC TO STABILIZE RATE; OR SO I THOUGHT. I PICKED UP THE CHART I HAD BEEN LOOKING AT BEFORE THE CALL FROM CTR. ABOUT A MIN LATER; FO SAID 'HEY; WE'RE CLBING.' I DROPPED THE CHART; NOTING THAT WE HAD ENTERED A SUBTLE CLB; OR AT LEAST SUBTLY ENTERED A CLB. IMMEDIATELY DISCONNECTED AUTOPLT AND PUSHED OVER AS GINGERLY AS I DARED WITH THE SEAT BELT LIGHT OFF. I'M NOT SURE HOW HIGH WE GOT; BUT IT WAS ABOVE INITIAL ALT. AS FAR AS I KNOW THERE WAS NO TFC CONFLICT; AND CTLR SAID NOTHING. MY OBSERVATIONS ON THIS EVENT: I WAS NEGLIGENT IN HOLDING THE CHART UP OBSCURING THE PANEL LONG ENOUGH FOR THIS TO HAPPEN; AND FOR NOT NOTING INCORRECT ANNUNCIATOR LIGHTS. I THINK THERE ARE SEVERAL FACTORS THAT MIGHT HAVE CONTRIBUTED. I WAS COMPLETELY UNFAMILIAR WITH ROA; HAVING NEVER BEEN ANYWHERE NEAR THERE BEFORE; AND IT IS A 'SPECIAL ARPT.' AS WE WERE EXPECTING A CHANCE OF THE WX BEING LOW IN RW/TRW; I WAS VERY CONCERNED WITH FAMILIARIZING MYSELF WITH TERRAIN; OBSTRUCTIONS; AND ALTERNATES. AT THE TIME OF THE EVENT I WAS LOOKING AT THE ORIENTATION OF POSSIBLE ALTERNATES ON THE ENRTE LOW CHART. FLT CTL PANEL MODE BUTTONS ARE TINY; AND VERY CLOSE TO EACH OTHER. ALMOST CERTAINLY I MUST HAVE PUSHED CLB VICE DSCNT; BUT THIS IS VERY EASY TO DO; AND ONE MUST BE VIGILANT TO LOOK FOR THE CORRECT ANNUNCIATOR LIGHT TO COME ON (OR GO OFF). AT THIS POINT I HAD LESS THAN 50 HRS IN TYPE ACFT SINCE TRANSITIONING/UPGRADING FROM CL65 WITH ENTIRELY DIFFERENT AUTOPLT CTLS. WE HAD JUST DONE A CONTINUOUS DUTY OVERNIGHT; LNDG AT DAY AT XA02 AM; AND DEPARTING DAY AT XF45 AM; WITH ABOUT 4 1/2 HRS ACTUAL REST TIME IN THE HOTEL. NEITHER OF US WAS AS SHARP AS WE WOULD NORMALLY BE.