FLC RESPONDS TO TCASII RA.

Narrative

DSNDING TO CMH FOR RWY 28L; CLRED TO 6000 FT (?). AT ABOUT 8000 FT; ATC CALLED TFC AT 12 O'CLOCK AND 7 (?) MI. TFC WAS ON TCASII; BUT WE COULDN'T SEE IT VISUALLY. TFC CLOSED; WE GOT 'TFC' (TA) FROM TCASII. THEN CTLR ISSUED TURN L TO 360 DEG HDG (ABOUT A 30 DEG L TURN). CAPT REACHED UP TO ROTATE HDG KNOB TO 360 DEGS BUT; BEFORE ACFT RESPONDED; WE GOT AN RA TO 'DSND.' I SAW TFC AT 12 O'CLOCK ON A COLLISION COURSE; SO I TOOK CTL; CLICKED OFF THE AUTOPLT; INCREASED THE DSCNT RATE AND TURNED L. MANEUVER WAS QUICK BUT NOT VIOLENT. LIGHT TWIN PASSED ABOUT 1 TO 1 1/2 MI R AND ABOUT 100 FT HIGH. AFTER CLR OF TFC; I PUT ACFT BACK ON AUTOPLT AND FORMALLY TRANSFERRED CTL BACK TO THE CAPT. CAPT WAS VERY MILDLY MIFFED AT ME FOR TAKING CTL; BUT I FELT THERE WAS NO TIME FOR DISCUSSION. THIS IS A TCASII SAVE; EVEN WITH SOME HELP FROM ATC. I SHOULD HAVE AT LEAST SAID 'TALLY-HO' OR SOMETHING TO LET HIM KNOW I WAS MANEUVERING BASED ON A VISUAL. EVADING (OR RESPONDING TO RA) USING AUTOPLT INPUTS WOULD HAVE BEEN TOO SLOW IN THIS CASE. I SHOULD HAVE COMMUNICATED BETTER; BUT I WOULD DO THE SAME THING AGAIN. CAPT AND I DISCUSSED COORD AND CTL AFTER WE LANDED. NO CLRNC DEV. TCASII IS SAVING LIVES EVERY DAY.