WDB ON APCH DSNDS BELOW PROPER ALT DUE TO WRONG ALTIMETER SETTING. TCASII RA.

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DURING DSCNT; CAPT INADVERTENTLY ENTERED 30.46 IN ALTIMETER WINDOW; INSTEAD OF 29.46 (CORRECT) THAT I HAD SET IN MY SIDE. PASSING THROUGH 13900 FT ON MY ALTIMETER; I NOTICED THAT THE ALT ARM BUTTON WAS STILL ILLUMINATED; SCOREBOARD SHOWED ARM; 'A' AUTOPLT STILL ENGAGED DSNDING IN EXCESS OF 2000 FPM. AS I LOOKED AT CAPT'S ALTIMETER I NOTICED WRONG SETTING AND YELLED ALTIMETER; LEVEL OFF; AT THE SAME INSTANT THE TCASII CALLED CLB; TFC; CLB! CAPT IMMEDIATELY DISENGAGED AUTOPLT; WHILE PULLING UP AND ADDING PWR AT THE SAME TIME TO ARREST THE DSCNT AT 14600 FT ON CAPT'S 13400 FT ON MY SIDE. TARGET ON MY 10 MI EXPANDED RADAR WAS LEVEL AT 13000 FT AT 1 O'CLOCK 1 MI INITIALLY AND SHOWED A RED SQUARE WITH A MINUS 7 ABOVE. THEN TCASII CALLED MONITOR VERT SPD AS WE CLBED BACK TO 14000 FT WITH CORRECT SETTING; THEN TCASII CALLED CLR OF CONFLICT; SHOWING TARGET AT 6 O'CLOCK AND 1 MI. NEITHER ACFT NOR APCH CTLR SAID ANYTHING AS APCH CTL WAS VERY BUSY. TCASII WORKED AS PUBLISHED. SUPPLEMENTAL INFO FROM ACN 263857: PRIOR TO THIS SIT I THOUGHT THE TCASII SYS TO BE NOTHING BUT A POORLY DESIGNED COCKPIT DISTR. DFW AND ATL HAVE DSCNTS TO 11000 FT WITH TFC CLBING TO 10000 FT AND ONE RECEIVES TA ALL THE TIME. I WAS IN FAVOR OF A SOFTWARE CHANGE TO ELIMINATE THIS PROB. I NOW BELIEVE NO CHANGE IS NECESSARY TO CORRECT THIS DESIGN. TCASII MAY HAVE SOME PROBS BUT IT IS SOUND IN THEORY AND SHOULD ONLY BE CHANGED AFTER CAREFUL THOUGHT AND A GOOD AMOUNT OF FEEDBACK.