MD11 CREW HAD CONFUSED NAV DISPLAY ON APCH AT ATL. ACFT HAD LESS THAN LEGAL SEPARATION FROM ANOTHER ACFT.

Narrative

PRIOR TO TOP OF DSCNT; ARR ATIS WAS ACQUIRED AND THE EXPECTED APCH (ILS RWY 8L) WAS ENTERED INTO THE FMS. THIS ALLOWS THE FMS TO TUNE AND IDENT THE SELECTED ILS AND SET THE CORRECT INBOUND COURSE FROM THE ILS DATABASE. DURING DSCNT; THE PF ENTERED 'PRESELECTS' INTO THE 'NAV/RAD' PAGE OF THE FMS AND ANNOUNCED SO DOING. THE PNF WAS PREOCCUPIED WITH OTHER DUTIES AND DID NOT VERIFY THE DATA ENTERED INTO THE 'NAV/RAD' PAGE. THE 'PRESELECTS' ON THE 'NAV/RAD' PAGE ALLOW THE PNF TO QUICKLY 'HARD TUNE' AN APCH IF THERE IS A LAST MIN RWY CHANGE. THE 'PRESELECTS' CONSIST OF RADIO IDENT OR FREQ AND INBOUND COURSE (EG; IABC/092 OR 109.3/092). IT IS POSSIBLE TO HARD TUNE THE EXPECTED ILS AND INBOUND COURSE AND STILL HAVE 'PRESELECTS' FOR OTHER RWYS. HARD TUNING THE EXPECTED ILS OR OTHER APCH IS CONSIDERED TECHNIQUE AND IS NOT CONSISTENTLY DONE AT OUR COMPANY. WHEN THE FMS HAS DECODED THE ILS IDENT; A DISPLAY ON THE PRIMARY FLT DISPLAY CHANGES FROM THE ILS FREQ TO THE ILS IDENT (EG; 109.3 TO IABC). THE PLT IS NOT REQUIRED TO LISTEN TO THE IDENT IN THIS CASE. WHEN THE ILS IDENT WAS OBSERVED ON THE PRIMARY FLT DISPLAY ON DOWNWIND LEG; THE PNF CALLED OUT 'ILS RWY 8L TUNED AND IDENTED.' ON DOGLEG (120 DEGS MAGNETIC) TO FINAL; THE ENTIRE CREW WAS SLIGHTLY DISTR WHEN THE PF REACHED ACROSS THE OVERHEAD PANEL AND DESELECTED THE L OUTBOARD AND INBOARD AND R INBOARD LONGITUDINAL STABILITY AUGMENTATION SYS INSTEAD OF CALLING FOR 'ENG ANTI-ICE ON.' THE NEED FOR ENG ANTI-ICE WAS ALREADY DISCUSSED AND THE PNF ASSURED THE PF THAT IT WOULD BE USED AS NECESSARY. THE TURBINE AIR TEMP NEVER WENT BELOW 16 DEGS C SO ENG ANTI-ICE WAS NEVER NECESSARY. THE ERROR WAS QUICKLY CORRECTED BY THE PF; BUT THE NOISE OF THE AUTOPLT DISCONNECT ALERT PROBABLY DROWNED OUT AN APCH CLRNC CALL. PRIOR TO LOC INTERCEPT; THE PNF SWITCHED HIS DISPLAY FROM 'MISSED APCH' MODE TO 'APCH' MODE TO CHK THE COURSE DEV INDICATOR. THIS TACTIC IS STRICTLY TECHNIQUE AND A HOLDOVER FROM HIS MD88 DAYS WHEN THE ACFT WERE NOT AS NAVIGATIONALLY ACCURATE (NO INS). THE IMMEDIATE CALL WAS 'THIS PICTURE IS BAD!' FOLLOWED CLOSELY BY 'YOU HAVE REVERSE SENSING.' WE WERE WITHIN 1 DOT OF THE LOC SO I ASKED APCH CTL IF WE WERE CLRED TO INTERCEPT THE LOC AND HE SAID 'YES; YOU'RE CLRED FOR THE ILS APCH TO RWY 8L.' MY NEXT CALL WAS 'YOU'RE ON THE LOC...COME L.' THE ACFT WAS BEING FLOWN THROUGH THE AUTOPLT AND I BELIEVE AT THIS POINT THE PF SELECTED THE 'APCH/LAND' MODE. THE PNF WAS 'HEAD DOWN' CHKING THE 'NAV/RAD' PAGE TO DETERMINE WHY THE LOC HAD REVERSE SENSING. IT HAD THE CORRECT RWY 8L ILS IDENT BUT AN INCORRECT COURSE OF 272 DEGS ON THE 'ILS/CRS' LINE. SINCE THE ILS WAS HARD TUNED WITH A BAD COURSE ENTERED; THE AUTOPLT ATTEMPTED TO FLY INBOUND ON A 272 DEG COURSE WHICH MEANT IT WAS TURNING THE ACFT TO THE L THROUGH ABOUT 050 DEGS MAGNETIC WHEN THE PF SELECTED HDG MODE AND CORRECTED BACK TO THE LOC. THE PNF CLRED THE HARD TUNED INFO AND THEN GOT BACK IN THE LOOP. THE HDG WAS NOW 150 DEGS MAGNETIC AND THE PNF SAID 'THAT'S TOO BIG OF A CUT...COME BACK L.' THIS WAS BEFORE BEING ABLE TO INTERPRET OUR POS RELATIVE TO THE NEW LOC INFO. THE APCH CTLR ASKED IF WE WERE INTERCEPTING THE LOC AND THE PNF SAID 'WE HAVE BAD SENSING ON THE LOC.' HE GAVE US A HDG OF 360 DEGS AND MAINTAIN 5000 FT. WE PROBABLY CAME WITHIN 3/4 - 1/2 MI OF A B727 ABOUT 800 FT ABOVE US ON A PARALLEL APCH. DURING AN APCH USING THE FMS DATABASE FOR TUNING; IDENTING AND SETTING THE INBOUND COURSE FOR THE ILS; THE MD11 ONLY DISPLAYS THE ILS IDENT (EG; IABC) WHEN YOU ARE READY FOR THE APCH. IF THE ILS IS ALSO HARD TUNED; THERE IS NO ADDITIONAL DISPLAY ON THE PRIMARY FLT DISPLAY OR THE NAV DISPLAY. IF THE HARD TUNED INBOUND COURSE IS INCORRECT; THE ONLY WAY TO DISCOVER IT IS TO CHK THE 'NAV/RAD' PAGE; USE THE 'APCH' MODE OF THE NAV DISPLAY; OR SELECT 'APCH/LAND' AND CHASE THE WRONG COURSE. IN A PERFECT WORLD (ONE WITHOUT CONFLICTING DEMANDS ON ONE'S ATTN); THE PNF WOULD HAVE CAUGHT THE MISTAKE EARLY ON BY XCHKING WHAT WAS ENTERED INTO THE 'NAV/RAD' PAGE. WHEN THIS RPTR IS THE PF; HE NEVER HARD TUNES THE ILS BUT HE DOES ENTER 'PRESELECTS' FOR OTHER POSSIBLE RWYS. THIS DIFFERENCE IN TECHNIQUE PROBABLY LESSENED THIS RPTR'S URGENCY TO XCHK THE 'NAV/RAD' PAGE.