HDG TRACK DEV.

Narrative

THE COPLT WAS FLYING THE ACFT BEING VECTORED FOR ILS 9L AT ORD. WE WERE ON DOWNWIND DSNDING FROM 6000 FT TO 4000 FT ON A 230 DEG HDG. I WAS TUNING THE ILS WHEN WE GOT A CALL FROM APCH CTL TO 'SLOW TO 170/HDG 260.' I'M SURE I READ BACK THE CTLR'S INSTRUCTIONS. BUT; AFTER IDENTING THE ILS AND WATCHING THE COPLT SET 170 IN THE SPD WINDOW; I WAS NO LONGER SURE OF THE HDG. I ASKED HIM WHAT THE HDG WAS AND HE REPLIED; '150 DEGS.' HE SEEMED SURE AND IT WAS A GOOD HDG FOR A BASE LEG; SO WE BEGAN A TURN TOWARD FINAL APCH. FOR SOME REASON; I DIDN'T FEEL COMFORTABLE AND DECIDED TO CONFIRM THE HDG WITH THE CTLR. THE CTLR PAUSED; SAID '270 -- WHAT IS YOUR HDG -- CLB AND MAINTAIN 5000.' HE THEN INSTRUCTED ANOTHER FLT TO DSND IMMEDIATELY TO 3000 FT. SEPARATION WAS ACHIEVED AND WE WERE PUT BACK IN THE LINE-UP FOR LNDG. STRICTLY HUMAN ERROR. I SHOULD HAVE CONFIRMED THE INSTRUCTIONS WITH THE CTLR AT THE FIRST INSTANCE OF DOUBT. NOT THE COPLT! EXCELLENT WORK BY THE CTLR TO REMAIN CALM AND SEPARATE THE ACFT. ALTHOUGH IT WAS CREW ERROR; I WOULD SAY THAT MULTIPLE CLRNCS TEND TO RUN TOGETHER -- IE; THE DSND; TURN; SLOW; ETC; TYPE OF CLRNC. IT WOULD MAKE IT EASIER TO REMEMBER AND UNDERSTAND IF THE INSTRUCTIONS WERE SEPARATED BY READBACK. THIS MAY NOT BE FEASIBLE IN AREAS LIKE ORD; BUT IT'S ALL I CAN COME UP WITH TO REDUCE MISUNDERSTANDINGS AND ERRORS.