AN ACR FLC FAILED TO FOLLOW A VECTOR CLRNC AS A RESULT OF HDG SELECT UTILIZATION OF THE AUTOFLT SYS; AND RECEIVED A TCASII ALERT.

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ENRTE STL TO JFK. FL370; AND 40-50 NM SW OF ROSEWOOD (ROD). TRACKING TO ROD ON 250 DEG RADIAL AND HDG 065 DEGS CTR TOLD US TO TURN L 15 DEGS; FOR TFC. CAPT TURNED HEAD SEL KNOB TO 050 DEGS; I OBSERVED. BANK WAS 10 DEGS. I PICKED UP CHART FOR FREQ OF DEYER (DJB). EXPECTING DIRECT DJB 'AFTER TFC;' SINCE THIS IS WHERE WE OFTEN RECEIVE CLRNC DIRECT TO DJB. AS I LOOKED UP; ACFT HAD TURNED TO APPROX 70 DEGS. CTR TOLD US TURN L TO 040 DEGS NOW. AT THE SAME TIME; TOLD ANOTHER ACR TO INCREASE RATE OF TURN. IN OUR TURN; WE VISUALLY NOTED THE TFC. TCASII ALERTED 'TFC;' ALSO; AT 1:30 POS. WE INCREASED BANK. TCASII SAID; DSND. AS CAPT STARTED TO DSND; THE TCASII STOPPED. THE TFC DID NOT GET CLOSER THAN THE OUTER EDGE OF TCASII SCREEN (12-14 MI). THIS WAS VERY GOOD DEMONSTRATION OF THE VALUE OF TCASII. THE AUTOFLT SYS OF THE MD80; WILL LULL ONE INTO A FALSE SENSE OF SECURITY. IT IS EASY TO THINK IT WILL ALWAYS WORK THE WAY WE THOUGHT WE PROGRAMMED IT. THIS SIT DEMONSTRATES THE NEED TO FOLLOW UP ON COMMANDS GIVEN TO AUTOFLT.