AN F900 CAPT; ON APCH TO HOU; NEGLECTED TO TURN AS CLRED; SPAWNING AN IMMEDIATE TURN REQUEST FROM ATC.

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DSNDING INTO HOU; ON THE ROKIT 5 ARR; I WAS INSTRUCTED TO CROSS THE FINAL FIX DRYLR; AND TURN TO HDG 310 DEGS. AS WE APCHED THE FIX; I WAS GETTING THE LATEST ATIS. PREMATURELY; THE ACFT COUPLED TO THE FMS AND STARTED A GENTLE TURN TOWARD ANOTHER FIX. WHEN I REALIZED WE WERE IN A TURN; I REACHED UP AND STARTED TURNING WHAT I THOUGHT WAS THE 'HDG KNOB.' IT WAS ACTUALLY THE AIRSPD KNOB. THE AIRSPD DECREASED AND THE ACFT KEPT TURNING. WHEN I REALIZED THE AUTOPLT WAS NOT DOING WHAT I WANTED IT TO DO; I DISCONNECTED IT AND STARTED A TURN BACK TO THE FIX. AT THAT TIME; ZHU INSTRUCTED ME TO MAKE AN 'IMMEDIATE L TURN;' WHICH I DID. AT NO TIME WERE WE IN IMMEDIATE DANGER; BUT WE MAY HAVE EXCEEDED; OR COME CLOSE TO EXCEEDING; HIS AIRSPACE. I HAVE BEEN FLYING THE G4 FOR THE PAST 11 YRS. I HAVE JUST COMPLETED MY OPERATING EXPERIENCE (100 HRS) AND AM NOW BACK FLYING THE FALSON 900EX WITH JUST OVER 100 HRS IN IT. THE COCKPIT AUTOPLT CTL PANEL LOOKS SIMILAR ON THE GX AND F900EX; BUT THE KNOBS AND DIALS ARE IN DIFFERENT PLACES; IE; HDG AND AIRSPD. THE CORRECTIVE ACTION I THOUGHT I WAS TAKING WAS ONLY MAKING THE SIT WORSE UNTIL I TOOK OVER MANUALLY. I CERTAINLY WISH THE UNITED STATES; CANADIAN; AND FRENCH COCKPIT DESIGNERS COULD COME UP WITH A MORE STANDARDIZED COCKPIT!