NMAC BTWN AN LTT RESPONDING TO A TCASII RA AND AN ACR CLBING IN RESPONSE TO ATC CLRNC. TCASII RESOLUTION DIRECTED A CLB RATHER THAN A DSCNT WHICH WOULD HAVE MORE EFFECTIVELY REMOVED THE CONFLICT.

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ACR Y FLT WAS AT OUR 2 O'CLOCK AND 10 MI. ATC CALLED TFC TO BOTH OF US. WE BOTH ANSWERED; 'ACFT IN SIGHT.' FLT XXX WAS AT 15000 FT. ATC GAVE FLT XXX A VISUAL CLB TO HIGHER ALT. FLT XXX ASKED WHAT OUR HDG WAS. IT TOOK A MIN OR SO FOR ATC TO ANSWER '310 DEGS.' ABOUT 2 MI SEPARATION; I COULD TELL WE WERE ON AN INTERCEPT COURSE. I STARTED TO LOOK AT THE TCASII TO SEE HIS ALT BECAUSE HE LOOKED TO BE CLBING. AT ABOUT THE SAME TIME THE TCASII CALLED 'TFC; TFC.' ALMOST IMMEDIATELY; IT CHANGED TO 'CLB; CLB.' MY FIRST THOUGHT WAS TO DSND SINCE FLT ACR Y WAS CLBING BUT SINCE I HAD NO WAY OF KNOWING IF HE WOULD STOP HIS CLB IF HE HAD TCASII; I FOLLOWED THE TCASII AND STARTED A CLB. THE TCASII WAS INDICATING ROUGHLY A 2000-3000 FPM CLB. AS I ROTATED THROUGH ABOUT 15 DEG PITCH-UP I STARTED A R TURN TO PASS BEHIND FLT ACR Y. DURING THIS TIME THE TCASII CALLED 'INCREASE CLB; INCREASE CLB;' AND INDICATED APPROX A 3500-4000 FPM CLB. AS I GOT TO ABOUT 30 DEGS OF BANK THE TCASII CHANGED TO 'DSND; DSND;' FOLLOWED SOON AFTER BY 'CLR OF CONFLICT.' DURING THE MANEUVER I REACHED 20-25 DEG PITCH UP; 3000-3500 FPM CLB; 30-40 DEG BANK. WE CLBED TO 17800 FT BEFORE LEVELING AND RETURNING TO 16000 FT. WHILE I UNDERSTAND ATC WAS WITHIN THEIR RIGHTS TO ISSUE THE VISUAL CLB TO FLT ACR Y; I FEEL THE RULE IS DANGEROUS BECAUSE IT IS NEARLY IMPOSSIBLE TO JUDGE AN ACFT'S DIRECTION AT NIGHT AND THE ABILITY TO JUDGE SEPARATION IS EXTREMELY IMPAIRED AT NIGHT. (NOTE: FLT ACR Y HAD TO ASK OUR HDG.) I THINK THESE FACTORS DIRECTLY LED TO FLT ACR Y STARTING AN ILL ADVISED CLB RIGHT INTO OUR FLT PATH.