ACR ON VISUAL APCH DSNDS BELOW GS AND EXITS TCA FLOOR.

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ON APCH TO ATL. CAPT HAND FLYING. FO WITH RAW DATA SELECTED TO COMPLY WITH RECENT PROC CHANGE. AT 3500 FT MSL APPROX 10-15 SE OF ATL VOR WITH PRECEDING TFC IN SIGHT; ATC CLRED US FOR VISUAL APCH. WE ARMED APCH MODE SO FLT DIRECTOR WOULD WORK ON SELECTED ILS FREQ WTS. GS CAPTURED AND CAPT DSNDED BELOW 3500 FT SETTING OFF ALT ALERT. SINCE 3500 FT IS PUBLISHED CLB OUT ALT AND WE WERE HAND FLYING A VISUAL APCH THAT IS WHERE WE WANTED THE MCP ALT. CAPT ASKED ABOUT A GATE AND I CALLED RAMP CTL DISTRACTING MYSELF (MY FAULT). ON SLOPE AT APPROX 2500- 2600 FT THE CAPT AND I BOTH THOUGHT WE LOOKED LOW AND LEVELED OFF TILL WE REINTERCEPTED A GOOD VISUAL GLIDE PATH. SIMULTANEOUSLY THE ILS GS CHANGED ITS WTS INDICATION AND SHOWED US LOW. WE WERE ON A VISUAL AND CAUSED NO CONFLICT; BUT TECHNICALLY WE DSNDED BELOW THE TCA FLOOR OF 3500 IN THAT AREA (I THINK). THE PROBLEMS: THE CAPT HAND FLEW AND DIDN'T MONITOR POS/ALT VERSUS THE HSI DISPLAY. THE FO (ME) CALLED FOR A GATE INSTEAD OF WATCHING; AND THE FO (ME) IS NOT ACCUSTOMED TO LOOKING AT RAW DATA ANY MORE. (I'VE BEEN ON LGT/WDB FOR ALMOST 2 YRS.)