FLC OF CPR ACFT MAKES INCORRECT RESPONSE TO TCASII COMMANDS.

Narrative

WE WERE APCHING WHITE PLAINS; NY; ON THE BUONO ARR; HAVING JUST BEEN GIVEN A VECTOR OFF OF THE ARR. ATC GAVE US AN ADVISORY OF TFC; THEN THE TCASII GAVE A TA. A FEW SECONDS LATER; THE TCASII GAVE AN RA 'MONITOR VERT SPD;' WITH A DISPLAY ON THE EADI OF A RED DSCNT LINE. THIS WAS THE HONEYWELL ED800 EADI WHICH DISPLAYS VERT SPD AS A GREEN LINE ABOVE AND BELOW CENTER. THE RED LINE EXTENDING BELOW CENTER BY TCASII MEANS DO NOT DSND. I MISINTERPED THIS AS A DSCNT COMMAND AND DISENGAGED THE AUTOPLT AND BEGAN DSNDING. BEFORE I HAD DSNDED MORE THAN 50 FT; THE CAPT (PNF) ADVISED ME OF MY ERROR AND PULLED BACK ON THE CTL YOKE TO BEGIN A CLB. WE CLBED ABOUT 200 FT; THEN THE RA CLRED. WHAT I SHOULD HAVE DONE WHEN I HEARD AND SAW THE RA WAS TO SIMPLY STAY LEVEL AT MY PRESENT ALT. THE AUDIO ANNUNCIATION 'MONITOR VERT SPD' INSINUATED TO ME THAT I SHOULD BE CLBING OR DSNDING -- THIS IS THE REASON I CLICKED OFF THE AUTOPLT. I HAD READ THE TCASII MANUAL AT SOME TIME BEFORE THIS HAPPENED. I THOUGHT I UNDERSTOOD THE SYS AND THE PROPER RESPONSE TO AN RA. IF SOMEONE ASKED ME WHAT THE PROPER REACTION TO THE SIT I EXPERIENCED WAS; I WOULD HAVE GIVEN THE CORRECT ANSWER. MY KNOWLEDGE WAS ALL RIGHT -- MY REACTION WAS NOT. THE TCASII ANNUNCIATION 'MONITOR VERT SPD' WHEN LEVEL IS MISLEADING. IT IMPLIES THERE SHOULD BE SOME VERT SPD. HOWEVER; WHEN LEVEL WITH ZERO VERT SPD IT BECOMES A NON SEQUITUR; THUS CONFUSING THE PLT. IT SHOULD SAY 'MAINTAIN PRESENT ALT' IF YOU AREN'T SUPPOSED TO DO ANYTHING WHILE LEVEL.