Narrative:

Initial approach controller gave us runway 4R for approach (ATIS reported 4R, 9R in use). First officer and I crew coordinated our approach plates and instruments and radios for 4 right. Position and direction of aircraft through radar vectors consistent with approach to 4R. Apparently, the final approach controller switched the approach to 9R but my first officer and myself all continued to hear 4R which we read back to the ATC on 3 occasions. Final approach controller gave us clearance to intercept localizer and maintain 2500 ft MSL until established, then cleared for ILS approach. Just then, radios tuned to 4R localizer and GS came alive and were followed. ATC said to report deana to ord tower. First officer checked approach chart and was about to query ATC when localizer and GS flags all showed unable to verify our position we tried to call ATC but frequency was in use. ATC then noticed our attempt to align with 4R and corrected the heading altitude for proper approach to 9R which was subsequently accomplished without further incident. I was in error in not verifying unmistakably the runway of intended use. However, we did read back 4R on 3 occasions with no correction from ATC, probably due to pressure of traffic flow into ord. No conflict arose at either end of the conversation to warn of potential misunderstanding. In retrospect, if the approach radar controller (final) had stated the approach was to 'niner' right, we would have instantly noticed it was not 4R, but 4 and 9 sound a lot alike in a busy radar environment. Also the coordination between initial and final approach controller left something to be desired. If the initial controller had told the final he had stated ILS 4R, the final could have stated 'change approach to niner right' eliminating the potential for confusion. This should be done because most crews set up for the instrument approach they are initially given and thereafter are predisposed to bias communications received to that particular runway unless specifically cued that a change to another approach is contemplated. This whole episode is a replay of a continuing scenario creeping into the system. Standard procedures and phrases designed for maximum safety lose their effectiveness when taken for granted by either the user of the airspace system or its mgrs.

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Original NASA ASRS Text

Title: ACR GIVEN APCH TO 4R. VECTORED AND SET UP APCH ACCORDINGLY. FINAL APCH CTLR SWITCHED TO 9R BUT CHANGE NOT EMPHASIZED, NOR PICKED UP BY FLC.

Narrative: INITIAL APCH CTLR GAVE US RWY 4R FOR APCH (ATIS RPTED 4R, 9R IN USE). FO AND I CREW COORDINATED OUR APCH PLATES AND INSTS AND RADIOS FOR 4 R. POS AND DIRECTION OF ACFT THROUGH RADAR VECTORS CONSISTENT WITH APCH TO 4R. APPARENTLY, THE FINAL APCH CTLR SWITCHED THE APCH TO 9R BUT MY FO AND MYSELF ALL CONTINUED TO HEAR 4R WHICH WE READ BACK TO THE ATC ON 3 OCCASIONS. FINAL APCH CTLR GAVE US CLRNC TO INTERCEPT LOC AND MAINTAIN 2500 FT MSL UNTIL ESTABLISHED, THEN CLRED FOR ILS APCH. JUST THEN, RADIOS TUNED TO 4R LOC AND GS CAME ALIVE AND WERE FOLLOWED. ATC SAID TO RPT DEANA TO ORD TWR. FO CHKED APCH CHART AND WAS ABOUT TO QUERY ATC WHEN LOC AND GS FLAGS ALL SHOWED UNABLE TO VERIFY OUR POS WE TRIED TO CALL ATC BUT FREQ WAS IN USE. ATC THEN NOTICED OUR ATTEMPT TO ALIGN WITH 4R AND CORRECTED THE HDG ALT FOR PROPER APCH TO 9R WHICH WAS SUBSEQUENTLY ACCOMPLISHED WITHOUT FURTHER INCIDENT. I WAS IN ERROR IN NOT VERIFYING UNMISTAKABLY THE RWY OF INTENDED USE. HOWEVER, WE DID READ BACK 4R ON 3 OCCASIONS WITH NO CORRECTION FROM ATC, PROBABLY DUE TO PRESSURE OF TFC FLOW INTO ORD. NO CONFLICT AROSE AT EITHER END OF THE CONVERSATION TO WARN OF POTENTIAL MISUNDERSTANDING. IN RETROSPECT, IF THE APCH RADAR CTLR (FINAL) HAD STATED THE APCH WAS TO 'NINER' R, WE WOULD HAVE INSTANTLY NOTICED IT WAS NOT 4R, BUT 4 AND 9 SOUND A LOT ALIKE IN A BUSY RADAR ENVIRONMENT. ALSO THE COORD BTWN INITIAL AND FINAL APCH CTLR LEFT SOMETHING TO BE DESIRED. IF THE INITIAL CTLR HAD TOLD THE FINAL HE HAD STATED ILS 4R, THE FINAL COULD HAVE STATED 'CHANGE APCH TO NINER R' ELIMINATING THE POTENTIAL FOR CONFUSION. THIS SHOULD BE DONE BECAUSE MOST CREWS SET UP FOR THE INST APCH THEY ARE INITIALLY GIVEN AND THEREAFTER ARE PREDISPOSED TO BIAS COMS RECEIVED TO THAT PARTICULAR RWY UNLESS SPECIFICALLY CUED THAT A CHANGE TO ANOTHER APCH IS CONTEMPLATED. THIS WHOLE EPISODE IS A REPLAY OF A CONTINUING SCENARIO CREEPING INTO THE SYS. STANDARD PROCS AND PHRASES DESIGNED FOR MAX SAFETY LOSE THEIR EFFECTIVENESS WHEN TAKEN FOR GRANTED BY EITHER THE USER OF THE AIRSPACE SYS OR ITS MGRS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.