ACR SPACE TOO CLOSE EXECUTES A MISSED APCH; CONFUSES CLRED ALT AND HAS RESULTING TFC CONFLICT.

Narrative

ORD APCH CTLR AND ORD TWR CTLR SEQUENCED US TOO CLOSE TO ANOTHER LNDG ACFT. ON FINAL; AT ABOUT 2 MI SEPARATION; I QUERIED THE TWR CTLR 'HOW DOES SPACING LOOK FOR US?' HE REPLIED 'IT LOOKS TIGHT.' I ALREADY HAD IN MIND THAT WE WOULD BE GOING AROUND. SHORTLY AFTER; WE RECEIVED THE GAR CLRNC. THE CTLR SAID 'TURN R TO A HDG OF ONE-FOUR-ZERO; CLB AND MAINTAIN ONE-FOUR-THOUSAND.' THE ALT SEEMED HIGH TO ME; SO I READ BACK; VERY DISTINCTLY; 'CLB TO ONE-FOUR THOUSAND' PLACING SPECIAL EMPHASIS ON THE 'ONE-FOUR-THOUSAND.' MY CAPT LATER SAID HE HAD DISTINCTLY HEARD ME. THE CTLR DID NOT CORRECT MY READBACK. AFTER SWITCHING TO ANOTHER APCH CTLR FOR SEQUENCING BACK TO ORD; AS WE WERE PASSING 6000 FT; I NOTICED TCASII TFC 2000 FT HIGHER THAN US. THEN I LOOKED OUT AND SAW THE B727 CRUISING AT 8000 FT AND XING OUR PATH FROM L TO R. THE CTLR ASKED US IF WE WERE GIVEN 4000 FT. WE SAID 'NO; 14000 FT.' THE CTLR SAID 'NO PROB; JUST LEVEL AT 6000 FOR TFC.' WE GOT A TA AT AROUND 6400 FT (NO RA) AND STARTED OUR DSCNT BACK TO 6000 FT. I BELIEVE THE PROB MAY HAVE BEEN WORKLOAD FOR THE CTLRS. IT WAS A BUSY TIME (AVERAGE; NOT UNUSUALLY HVY FOR ORD). THE ORIGINAL APCH CTLR KEPT US HIGH TOO LONG AND FORGOT TO CLR US FOR THE ILS APCH. AFTER HE DID; WE WERE TOLD TO KEEP OUR SPD UP. I HAD BEEN MONITORING THE SPACING BTWN US AND THE ACFT IN FRONT OF US ON FINAL. SPACING LOOKED TOO CLOSE TO ME. WHEN I SWITCHED TO TWR; HE CLRED US TO LAND; MAKING NO MENTION OF THE AIRPLANE IN FRONT OF US. I TRULY THOUGHT AT THE TIME HE DIDN'T KNOW WHERE WE WERE; PERHAPS CONFUSING OUR LOCATION WITH ANOTHER AIRPLANE. WHEN I COULD GET A WORD IN; AND KNOWING IT WAS ALREADY THE CTLR ABOUT THE SPACING. HIS REPLY WAS THE FIRST INDICATION HE GAVE US THAT HE THOUGHT THERE WOULD BE A PROB. I THINK IT MAY HAVE BEEN HIS FIRST REALIZATION THERE WAS A PROB WITH SPACING. WHEN HE GAVE US THE GAR INSTRUCTIONS; HE SEEMED FLUSTERED. I BELIEVE THE MISTAKE WAS INCORRECTLY SAYING 'ONE-FOUR-THOUSAND' IMMEDIATELY AFTER SAYING 'ONE-FOUR-ZERO.'