Narrative:

The event occurred while shooting the ILS approach to runway 8L in atl. ATC told us to fly 180 KTS until crossing the marker and to descend to 3500' on a heading of 120 degree to intercept the localizer inbound. The problem started because we were descending from 6000' MSL and were high and fast for the distance to atl. We were shooting a coupled approach because of the WX conditions in atl. On a 120 degree heading I selected navigation localizer on the large transport autoplt because we were cleared to intercept the localizer but not the approach. The autoplt and 'F/D' showed capture indications and initiated a left turn, but at only 15 degree angle of bank. This caused some momentary confusion on my part and I did not know if I should believe the F/D or the autoplt inputs. At this time atl approach told us that we had flown through the localizer and to turn left to 060 degree heading to reintercept the localizer inbound and that we were cleared for the approach. I went back to the turn knob mode to a 060 degree heading and reengaged the autoplt in the automatic GS mode. The autoplt flew into a capture but again went through the inbound course. I had just disconnected the autoplt to fly manually when atl approach told us to go missed approach. We shot the missed approach and the RVR was reported 5000' so I flew a manual ILS with no further problems. Supplemental information from acn 139374. Flew across parallel runway (9R) final approach course.

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Original NASA ASRS Text

Title: ACR-LGT OVERSHOT LOC DURING VECTORS TO ILS AT ATL. MULTIPLE PARALLEL RWY APCHS IN PROGRESS.

Narrative: THE EVENT OCCURRED WHILE SHOOTING THE ILS APCH TO RWY 8L IN ATL. ATC TOLD US TO FLY 180 KTS UNTIL XING THE MARKER AND TO DSND TO 3500' ON A HDG OF 120 DEG TO INTERCEPT THE LOC INBND. THE PROB STARTED BECAUSE WE WERE DSNDING FROM 6000' MSL AND WERE HIGH AND FAST FOR THE DISTANCE TO ATL. WE WERE SHOOTING A COUPLED APCH BECAUSE OF THE WX CONDITIONS IN ATL. ON A 120 DEG HDG I SELECTED NAV LOC ON THE LGT AUTOPLT BECAUSE WE WERE CLRED TO INTERCEPT THE LOC BUT NOT THE APCH. THE AUTOPLT AND 'F/D' SHOWED CAPTURE INDICATIONS AND INITIATED A LEFT TURN, BUT AT ONLY 15 DEG ANGLE OF BANK. THIS CAUSED SOME MOMENTARY CONFUSION ON MY PART AND I DID NOT KNOW IF I SHOULD BELIEVE THE F/D OR THE AUTOPLT INPUTS. AT THIS TIME ATL APCH TOLD US THAT WE HAD FLOWN THROUGH THE LOC AND TO TURN LEFT TO 060 DEG HDG TO REINTERCEPT THE LOC INBND AND THAT WE WERE CLRED FOR THE APCH. I WENT BACK TO THE TURN KNOB MODE TO A 060 DEG HDG AND REENGAGED THE AUTOPLT IN THE AUTO GS MODE. THE AUTOPLT FLEW INTO A CAPTURE BUT AGAIN WENT THROUGH THE INBND COURSE. I HAD JUST DISCONNECTED THE AUTOPLT TO FLY MANUALLY WHEN ATL APCH TOLD US TO GO MISSED APCH. WE SHOT THE MISSED APCH AND THE RVR WAS RPTED 5000' SO I FLEW A MANUAL ILS WITH NO FURTHER PROBS. SUPPLEMENTAL INFO FROM ACN 139374. FLEW ACROSS PARALLEL RWY (9R) FINAL APCH COURSE.

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.