Narrative:

At the time stl was using runway 30R for landing, and taking off on runway 30L. Parallel approachs were not being used because of the low ceiling. We were cleared for an ILS approach to runway 30 right with the first officer flying the aircraft. It is common for the captain and first officer to alternate legs, and it was his turn. The WX conditions were not bad enough to require a monitored approach: therefore, the first officer would fly the entire approach and landing. The approach was normal until just inside the OM, at which point we started drifting to the left. The first officer corrected back to the localizer, but on returning to the original heading we drifted very rapidly to the left again. By this time, since we were getting close to minimums and still in the clouds, I had decided that we would go around. Before I could verbalize my thoughts the first officer said, 'we had better go around,' (or something to that effect) and I responded: 'go around.' which he did. Stl vectored us around for another approach and we landed on runway 30 right, without incident. Supplemental information from acn 298105: as I proceeded along the approach, I started to deviation to the right (north) of the localizer. I began to correct towards the localizer, and in so doing, recaptured the localizer. At this point I began to track away from the localizer to the left (south) at an unusually fast rate, even given the crosswind from the right (350 degrees at 10 KTS at a point before approach minimums I elected to make a missed approach. The localizer behaved in a most peculiar manner, in its rate of movement. Whether this erratic localizer behavior was a result of internal or external navigation equipment failure, cellular phone usage, or pilot induced oscillation, I can't say, but something was odd, and I believe a missed approach was necessary.

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Original NASA ASRS Text

Title: AN ACR FLC EXPERIENCED DRIFT WHILE FAF INBOUND, ON AN ILS APCH. JUST PRIOR TO MINIMUMS, THE LOC RATE OF DEFLECTION CHANGE WAS SO SIGNIFICANT THAT A MISSED APCH WAS EXECUTED.

Narrative: AT THE TIME STL WAS USING RWY 30R FOR LNDG, AND TAKING OFF ON RWY 30L. PARALLEL APCHS WERE NOT BEING USED BECAUSE OF THE LOW CEILING. WE WERE CLRED FOR AN ILS APCH TO RWY 30 R WITH THE FO FLYING THE ACFT. IT IS COMMON FOR THE CAPT AND FO TO ALTERNATE LEGS, AND IT WAS HIS TURN. THE WX CONDITIONS WERE NOT BAD ENOUGH TO REQUIRE A MONITORED APCH: THEREFORE, THE FO WOULD FLY THE ENTIRE APCH AND LNDG. THE APCH WAS NORMAL UNTIL JUST INSIDE THE OM, AT WHICH POINT WE STARTED DRIFTING TO THE L. THE FO CORRECTED BACK TO THE LOC, BUT ON RETURNING TO THE ORIGINAL HDG WE DRIFTED VERY RAPIDLY TO THE L AGAIN. BY THIS TIME, SINCE WE WERE GETTING CLOSE TO MINIMUMS AND STILL IN THE CLOUDS, I HAD DECIDED THAT WE WOULD GAR. BEFORE I COULD VERBALIZE MY THOUGHTS THE FO SAID, 'WE HAD BETTER GAR,' (OR SOMETHING TO THAT EFFECT) AND I RESPONDED: 'GAR.' WHICH HE DID. STL VECTORED US AROUND FOR ANOTHER APCH AND WE LANDED ON RWY 30 R, WITHOUT INCIDENT. SUPPLEMENTAL INFO FROM ACN 298105: AS I PROCEEDED ALONG THE APCH, I STARTED TO DEV TO THE R (N) OF THE LOC. I BEGAN TO CORRECT TOWARDS THE LOC, AND IN SO DOING, RECAPTURED THE LOC. AT THIS POINT I BEGAN TO TRACK AWAY FROM THE LOC TO THE L (S) AT AN UNUSUALLY FAST RATE, EVEN GIVEN THE XWIND FROM THE R (350 DEGS AT 10 KTS AT A POINT BEFORE APCH MINIMUMS I ELECTED TO MAKE A MISSED APCH. THE LOC BEHAVED IN A MOST PECULIAR MANNER, IN ITS RATE OF MOVEMENT. WHETHER THIS ERRATIC LOC BEHAVIOR WAS A RESULT OF INTERNAL OR EXTERNAL NAV EQUIP FAILURE, CELLULAR PHONE USAGE, OR PLT INDUCED OSCILLATION, I CAN'T SAY, BUT SOMETHING WAS ODD, AND I BELIEVE A MISSED APCH WAS NECESSARY.

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.