Narrative:

On a 330 degree heading at 6000' to intercept runway 30L localizer at stl, crossing the mississippi river south of the gateway arch we were advised of medium large transport Y at 2:30 to 3 O'clock on a parallel approach to 30R. He was 1000' below us. Traffic was sighted and approach control was so advised. Flight visibility was hazy and about 3 to 5 mi with ground contact but the airport was not in sight. We were cleared for 30L ILS to maintain 2200' or higher until established on the localizer and to maintain 190 KTS to the outer marker. We visually sighted the runway in the descent and turned so as not to intercept the localizer but to remain slightly south of the runway centerline. Realizing that the parallel runways are close together, the captain elected to wait to center the localizer until he reconfirmed the position of medium large transport Y that was making the parallel approach. At the same time that I was going to alert the captain that medium large transport Y was getting too close he looked out the side window and saw medium large transport Y correcting back to the 30R localizer at a distance of approximately 100' above and 500' horizontally from us in a 20 to 30 degree bank to the right. This incident could have been avoided if the intercepts to the parallel locs had been staggered; i.e. Not wing tip to wing tip. For an airport like stl-lambert where parallel runways are too close together, simultaneous approachs should only be made with staggered intercepts. It is much easier and safer to visually maintain contact with your traffic if it is in front of you vs on your wing at 9 or 3 O'clock.

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Original NASA ASRS Text

Title: ACR MLG THAT STRAYED OFF THE FINAL APCH COURSE WHILE ON PARALLEL ILS APCH. CAUSES CONFLICT.

Narrative: ON A 330 DEG HDG AT 6000' TO INTERCEPT RWY 30L LOC AT STL, XING THE MISSISSIPPI RIVER S OF THE GATEWAY ARCH WE WERE ADVISED OF MLG Y AT 2:30 TO 3 O'CLOCK ON A PARALLEL APCH TO 30R. HE WAS 1000' BELOW US. TFC WAS SIGHTED AND APCH CTL WAS SO ADVISED. FLT VISIBILITY WAS HAZY AND ABOUT 3 TO 5 MI WITH GND CONTACT BUT THE ARPT WAS NOT IN SIGHT. WE WERE CLRED FOR 30L ILS TO MAINTAIN 2200' OR HIGHER UNTIL ESTABLISHED ON THE LOC AND TO MAINTAIN 190 KTS TO THE OUTER MARKER. WE VISUALLY SIGHTED THE RWY IN THE DSCNT AND TURNED SO AS NOT TO INTERCEPT THE LOC BUT TO REMAIN SLIGHTLY SOUTH OF THE RWY CENTERLINE. REALIZING THAT THE PARALLEL RWYS ARE CLOSE TOGETHER, THE CAPT ELECTED TO WAIT TO CENTER THE LOC UNTIL HE RECONFIRMED THE POS OF MLG Y THAT WAS MAKING THE PARALLEL APCH. AT THE SAME TIME THAT I WAS GOING TO ALERT THE CAPT THAT MLG Y WAS GETTING TOO CLOSE HE LOOKED OUT THE SIDE WINDOW AND SAW MLG Y CORRECTING BACK TO THE 30R LOC AT A DISTANCE OF APPROX 100' ABOVE AND 500' HORIZONTALLY FROM US IN A 20 TO 30 DEG BANK TO THE RIGHT. THIS INCIDENT COULD HAVE BEEN AVOIDED IF THE INTERCEPTS TO THE PARALLEL LOCS HAD BEEN STAGGERED; I.E. NOT WING TIP TO WING TIP. FOR AN ARPT LIKE STL-LAMBERT WHERE PARALLEL RWYS ARE TOO CLOSE TOGETHER, SIMULTANEOUS APCHS SHOULD ONLY BE MADE WITH STAGGERED INTERCEPTS. IT IS MUCH EASIER AND SAFER TO VISUALLY MAINTAIN CONTACT WITH YOUR TFC IF IT IS IN FRONT OF YOU VS ON YOUR WING AT 9 OR 3 O'CLOCK.

Data retrieved from NASA's ASRS site as of August 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.