Narrative:

While on a 240 degree vector to final approach course to runway 21L at dtw, we were cleared to 'maintain 5000 ft until robbi, cleared for the ILS runway 21 approach.' the FCU appr (approach) push button was pushed and the autoplt was armed to capture the localizer course and the GS. The GS was captured before the localizer course and descent from 5000 ft was initiated by the autoplt. While I attempted to determine if we had passed 'robbi,' we flew through the localizer course (the autoflt system did not capture the localizer for reasons unknown). As I used the heading control knob of the FCU to turn back to the localizer course, a TA followed by an RA was generated by the TCASII system for an aircraft below us on the parallel approach (runway 21R). We leveled off at approximately 4600 ft MSL and continued the turn back to the localizer course and intercepted the facility. When established on the localizer (well above the GS) and after the TCASII aural 'clear of conflict' message was received, I disconnected the autoflt system and flew the aircraft down to the GS and continued the approach to a landing in VMC. The incident was initiated by a failure of the autoplt to capture the localizer course. This may have resulted from my possibly pulling the FCU heading control knob after the approach push button had been pushed and the localizer and GS armed for autoplt capture. This was exacerbated by my failure to recognize the failure to capture the localizer sooner. That was because I became preoccupied with identing 'robbi' (our 5000 ft restr). The ILS runway 21L has no DME and robbi was not displayed on our EFIS navigation display (a 'via' had not been selected on the FMGC approach menu). 'Robbi' is idented by the crl VOR/DME which was not manually tuned, and both VOR receivers were automatic tuned to dxo VOR/DME. The A320 FMGC is programmed to allow the autoflt system to capture the GS signal prior to the localizer signal which can cause a descent to be initiated before the aircraft is established on the facility. Another mistake made was my failure to disconnect the autoplt immediately following the TCASII RA. This resulted in a slower divergence from the RA traffic and a slower correction back onto the GS, resulting in a high rate of descent once the autoplt was disconnected.

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Original NASA ASRS Text

Title: A320 ACFT ON VECTOR HEADING FOR INTERCEPT AND ALT RESTR, ACFT ARMED FOR APCH CAPTURES GS PRIOR TO LOC INTERCEPT AND COMMENCES DSCNT BELOW ASSIGNED. TCASII RA ALERTS FLC TO ANOTHER ACFT ON APCH TO PARALLEL RWY. RPTR CAPT SAYS HE MAY HAVE PULLED INSTEAD OF PUSHING THE FCU (FLT CTL UNIT).

Narrative: WHILE ON A 240 DEG VECTOR TO FINAL APCH COURSE TO RWY 21L AT DTW, WE WERE CLRED TO 'MAINTAIN 5000 FT UNTIL ROBBI, CLRED FOR THE ILS RWY 21 APCH.' THE FCU APPR (APCH) PUSH BUTTON WAS PUSHED AND THE AUTOPLT WAS ARMED TO CAPTURE THE LOC COURSE AND THE GS. THE GS WAS CAPTURED BEFORE THE LOC COURSE AND DSCNT FROM 5000 FT WAS INITIATED BY THE AUTOPLT. WHILE I ATTEMPTED TO DETERMINE IF WE HAD PASSED 'ROBBI,' WE FLEW THROUGH THE LOC COURSE (THE AUTOFLT SYS DID NOT CAPTURE THE LOC FOR REASONS UNKNOWN). AS I USED THE HEADING CTL KNOB OF THE FCU TO TURN BACK TO THE LOC COURSE, A TA FOLLOWED BY AN RA WAS GENERATED BY THE TCASII SYS FOR AN ACFT BELOW US ON THE PARALLEL APCH (RWY 21R). WE LEVELED OFF AT APPROX 4600 FT MSL AND CONTINUED THE TURN BACK TO THE LOC COURSE AND INTERCEPTED THE FAC. WHEN ESTABLISHED ON THE LOC (WELL ABOVE THE GS) AND AFTER THE TCASII AURAL 'CLR OF CONFLICT' MESSAGE WAS RECEIVED, I DISCONNECTED THE AUTOFLT SYS AND FLEW THE ACFT DOWN TO THE GS AND CONTINUED THE APCH TO A LNDG IN VMC. THE INCIDENT WAS INITIATED BY A FAILURE OF THE AUTOPLT TO CAPTURE THE LOC COURSE. THIS MAY HAVE RESULTED FROM MY POSSIBLY PULLING THE FCU HEADING CTL KNOB AFTER THE APCH PUSH BUTTON HAD BEEN PUSHED AND THE LOC AND GS ARMED FOR AUTOPLT CAPTURE. THIS WAS EXACERBATED BY MY FAILURE TO RECOGNIZE THE FAILURE TO CAPTURE THE LOC SOONER. THAT WAS BECAUSE I BECAME PREOCCUPIED WITH IDENTING 'ROBBI' (OUR 5000 FT RESTR). THE ILS RWY 21L HAS NO DME AND ROBBI WAS NOT DISPLAYED ON OUR EFIS NAV DISPLAY (A 'VIA' HAD NOT BEEN SELECTED ON THE FMGC APCH MENU). 'ROBBI' IS IDENTED BY THE CRL VOR/DME WHICH WAS NOT MANUALLY TUNED, AND BOTH VOR RECEIVERS WERE AUTO TUNED TO DXO VOR/DME. THE A320 FMGC IS PROGRAMMED TO ALLOW THE AUTOFLT SYS TO CAPTURE THE GS SIGNAL PRIOR TO THE LOC SIGNAL WHICH CAN CAUSE A DSCNT TO BE INITIATED BEFORE THE ACFT IS ESTABLISHED ON THE FAC. ANOTHER MISTAKE MADE WAS MY FAILURE TO DISCONNECT THE AUTOPLT IMMEDIATELY FOLLOWING THE TCASII RA. THIS RESULTED IN A SLOWER DIVERGENCE FROM THE RA TFC AND A SLOWER CORRECTION BACK ONTO THE GS, RESULTING IN A HIGH RATE OF DSCNT ONCE THE AUTOPLT WAS DISCONNECTED.

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.