ACR MD80S FLC ENCOUNTER LOC FLUCTUATIONS WHILE CONDUCTING AN ORD ILS RWY 4R APCH. DEFLECTIONS ENCOUNTERED SOON AFTER INTERCEPTING LOC. VISUAL APCH ASSIGNED WHEN ARPT OR TFC WAS SIGHTED.

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RWY 4R LOC DEFLECTIONS EXPERIENCED ON FINAL APCH. WX VMC AND CLRED FOR VISUAL APCH. HOWEVER; IF IT HAD BEEN IMC INSIDE THE FAF; A GAR DUE TO LOC DEFLECTIONS MIGHT HAVE BEEN REQUIRED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CONCERNED WITH WHAT HE PERCEIVES AS CONSTANT AND ERRATIC LOC DEFLECTIONS FOR MOST ILS'S CONDUCTED AT ORD. RPTR RECOGNIZES MD80S 'STRAY ELECTRON' ANOMALY. BUT HE ALSO HAS PROB WITH THE WAY ATC HANDLES THESE TYPES OF COMPLAINTS -- LOC DEFLECTIONS. EVEN THOUGH THE PLT RPTS THE PROB; PLT OBSERVES THAT IF VISUAL APCH CRITERIA EXISTS; TRACON STILL HAS THE PLT INTERCEPT THE LOC UNTIL TFC OR ARPT IS IN SIGHT. WITH THE TFC/ARPT IN SIGHT; ALL THINGS 'GO AWAY;' FOR THE ACFT CAN PROCEED VISUALLY TO THE ARPT. BUT THE PLT IS CONCERNED WITH THAT PERIOD OF TIME WHEN HE HAS TO DEPEND ON THE LOC FOR COURSE GUIDANCE (COMPANY PROCS) AND BEGINS TO SEE THE DEFLECTIONS OCCUR. RPTR IS CONCERNED IF HE 'DRIFTS' INTO PROTECTED AIRSPACE OF ANOTHER ACFT AND IS VIOLATED. THE PLT MUST WEIGH THE PROBABILITIES IN SMOOTHING OUT THE DEFLECTIONS; ASK ATC FOR CLARIFICATION FOR ANOTHER CLRNC OR EXECUTE A GAR. RPTR 'KNOWS' THAT WHEN VISUAL CRITERIA EXISTS; TWR NO LONGER PROTECTS THE ILS CRITICAL AREA AND ACFT TAXI THROUGH THAT AREA. RPTR BELIEVES THIS MAY HAVE SOMETHING TO DO WITH THE PROB. THE RPTR ALSO UNDERSTANDS THE 'MOVEMENT OF COMMERCE;' AND EVERYONE MUST 'MAKE DO.' RPTR WONDERS IF THERE CAN BE ENOUGH TIME TO MAKE A DECISION; CONSIDERING ALL THE FACTORS; AND NOT GET INTO A 'VIOLATION.' ON A SECOND CALLBACK CONVERSATION; ATCT SPECIALIST ADVISES THAT THE POSITIONING OF THE RWY 4R LOC WAS APPROX 120 FT CLOSER TO THE RWY THAN OTHER RWYS DUE TO THE HWY. THE SPECIALIST ADVISED THAT WHEN WDB ACFT EXIT RWY 4R AT THE END; THEY TURN MORE OR LESS PERPENDICULAR TO THE LOC AS THEY TAXI ONTO TXWY Q AND D. THEIR SIZE AND THE PHYSICAL PROX TO THE LOC IS KNOWN TO CAUSE A MOMENTARY INTERRUPT IN THE LOC SIGNAL. ALSO; THIS INFO IS ALLEGEDLY DISSEMINATED TO THE USERS. THE SPECIALIST ALSO ADVISED THAT DUE TO THIS ANOMALY; SOME AIRLINES HAVE ISSUED COMPANY BULLETINS NOT AUTHORIZING COUPLED APCHS TO RWY 4R.