Narrative:

We were flying the localizer back course to the runway. I was PF. I had briefed the localizer back course to runway xx. As we were commencing the approach we were told there were 2 pilatus aircraft in the approach pattern. I had slowed to 170 KTS and was on the localizer. I was told to follow one of the pilatus aircraft and could not descend until the other pilatus had passed the approach path. When I was cleared the approach I was distraction and pressed the VOR/localizer button. I immediately hit the heading select button and steered the jet back to the localizer course. I was not sure if the front course was in but after checking again we had 100 course in the selector. I could not understand why the jet had turned away from the course and had lost confidence in the ability of the flight directors to correctly follow the localizer; so I began to follow the LNAV course. As we approached the decision altitude we broke out and had ground contact. We were about 1 1/2 dots off the localizer to the left of course. I saw the approach lights and steered the jet to them and disconnected the autoplt and landed uneventfully. After we landed and debriefed; I knew that I had made a mistake and should not have selected the VOR/localizer button that the jet would fly to the front course and turn in the wrong direction. The first officer did not understand until I explained it to him. I asked why the ILS was not being used in the low visibility; and the tower stated that there was a large windshear in that direction.

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Original NASA ASRS Text

Title: A B737-300 PILOT FLYING A LOC-BC SELECTED VOR/LOC WITH THE FRONT COURSE SELECTED AND THE FLT DIR INDICATED AN OPPOSITE DIRECTION TURN AWAY FROM THE LOC.

Narrative: WE WERE FLYING THE LOC BACK COURSE TO THE RWY. I WAS PF. I HAD BRIEFED THE LOC BACK COURSE TO RWY XX. AS WE WERE COMMENCING THE APCH WE WERE TOLD THERE WERE 2 PILATUS ACFT IN THE APCH PATTERN. I HAD SLOWED TO 170 KTS AND WAS ON THE LOC. I WAS TOLD TO FOLLOW ONE OF THE PILATUS ACFT AND COULD NOT DSND UNTIL THE OTHER PILATUS HAD PASSED THE APCH PATH. WHEN I WAS CLRED THE APCH I WAS DISTR AND PRESSED THE VOR/LOC BUTTON. I IMMEDIATELY HIT THE HDG SELECT BUTTON AND STEERED THE JET BACK TO THE LOC COURSE. I WAS NOT SURE IF THE FRONT COURSE WAS IN BUT AFTER CHKING AGAIN WE HAD 100 COURSE IN THE SELECTOR. I COULD NOT UNDERSTAND WHY THE JET HAD TURNED AWAY FROM THE COURSE AND HAD LOST CONFIDENCE IN THE ABILITY OF THE FLT DIRECTORS TO CORRECTLY FOLLOW THE LOC; SO I BEGAN TO FOLLOW THE LNAV COURSE. AS WE APCHED THE DECISION ALT WE BROKE OUT AND HAD GND CONTACT. WE WERE ABOUT 1 1/2 DOTS OFF THE LOC TO THE L OF COURSE. I SAW THE APCH LIGHTS AND STEERED THE JET TO THEM AND DISCONNECTED THE AUTOPLT AND LANDED UNEVENTFULLY. AFTER WE LANDED AND DEBRIEFED; I KNEW THAT I HAD MADE A MISTAKE AND SHOULD NOT HAVE SELECTED THE VOR/LOC BUTTON THAT THE JET WOULD FLY TO THE FRONT COURSE AND TURN IN THE WRONG DIRECTION. THE FO DID NOT UNDERSTAND UNTIL I EXPLAINED IT TO HIM. I ASKED WHY THE ILS WAS NOT BEING USED IN THE LOW VISIBILITY; AND THE TWR STATED THAT THERE WAS A LARGE WINDSHEAR IN THAT DIRECTION.

Data retrieved from NASA's ASRS site as of January 2009 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.