Narrative:

We were approaching white plains, ny, on the buono arrival, having just been given a vector off of the arrival. ATC gave us an advisory of traffic, then the TCASII gave a TA. A few seconds later, the TCASII gave an RA 'monitor vertical speed,' with a display on the eadi of a red descent line. This was the honeywell ED800 eadi which displays vertical speed as a green line above and below center. The red line extending below center by TCASII means do not descend. I misinterped this as a descent command and disengaged the autoplt and began descending. Before I had descended more than 50 ft, the captain (PNF) advised me of my error and pulled back on the control yoke to begin a climb. We climbed about 200 ft, then the RA cleared. What I should have done when I heard and saw the RA was to simply stay level at my present altitude. The audio annunciation 'monitor vertical speed' insinuated to me that I should be climbing or descending -- 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 system and the proper response to an RA. If someone asked me what the proper reaction to the situation I experienced was, I would have given the correct answer. My knowledge was all right -- my reaction was not. The TCASII annunciation 'monitor vertical speed' when level is misleading. It implies there should be some vertical speed. However, when level with zero vertical speed it becomes a non sequitur, thus confusing the pilot. It should say 'maintain present altitude' if you aren't supposed to do anything while level.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.