Narrative:

Uneventful descent and ILS intercept, except head sel button fell of on descent and could not be retrieved. Shortly after OM passage first officer disengaged autoplt 'to practice.' captain asked first officer to reengage so not to chance a go around at minimums. We were set up for 200' AGL decision height making a coupled approach as advised by company policy. First officer immediately reengaged the autoplt. Captain noticed G/south capture, but heading select engaged with no localizer armed or localizer capture indicated. Approach mode was properly engaged and 3 autoplts engaged. Captain advised copilot or the situation and asked him to reset. No change. Next first officer turned off autoplt and reset FD's. FD's engaged, G/south and localizer green. FD showed slightly low but on course, as did raw data. Correction made immediately and decision made to continue FD hand-flown approach. At 200' above minimums all appears normal and first officer acknowledged same. At minimums ground visibility was good and fwd visibility at least 1/2 mi. Runway and approach lights should have been in sight, but weren't. Captain told first officer, 'go around.' first officer executed same. Tower advised. Issued 200 degree heading climb to 5000'. Next approach to same runway coupled to minimums is uneventful. Discussed matter with avionics mechanic. So far unable to ascertain why autoplt approach mode could not be reengaged nor why aircraft was off course to right at minimums.

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Original NASA ASRS Text

Title: ACR WDB MAE A GO AROUND WHEN APCH ENVIRONMENT NOT IN SIGHT AT MINIMUMS.

Narrative: UNEVENTFUL DSNT AND ILS INTERCEPT, EXCEPT HEAD SEL BUTTON FELL OF ON DSNT AND COULD NOT BE RETRIEVED. SHORTLY AFTER OM PASSAGE F/O DISENGAGED AUTOPLT 'TO PRACTICE.' CAPT ASKED F/O TO REENGAGE SO NOT TO CHANCE A GAR AT MINIMUMS. WE WERE SET UP FOR 200' AGL DECISION HEIGHT MAKING A COUPLED APCH AS ADVISED BY COMPANY POLICY. F/O IMMEDIATELY REENGAGED THE AUTOPLT. CAPT NOTICED G/S CAPTURE, BUT HDG SELECT ENGAGED WITH NO LOC ARMED OR LOC CAPTURE INDICATED. APCH MODE WAS PROPERLY ENGAGED AND 3 AUTOPLTS ENGAGED. CAPT ADVISED COPLT OR THE SITUATION AND ASKED HIM TO RESET. NO CHANGE. NEXT F/O TURNED OFF AUTOPLT AND RESET FD'S. FD'S ENGAGED, G/S AND LOC GREEN. FD SHOWED SLIGHTLY LOW BUT ON COURSE, AS DID RAW DATA. CORRECTION MADE IMMEDIATELY AND DECISION MADE TO CONTINUE FD HAND-FLOWN APCH. AT 200' ABOVE MINIMUMS ALL APPEARS NORMAL AND F/O ACKNOWLEDGED SAME. AT MINIMUMS GND VISIBILITY WAS GOOD AND FWD VISIBILITY AT LEAST 1/2 MI. RWY AND APCH LIGHTS SHOULD HAVE BEEN IN SIGHT, BUT WEREN'T. CAPT TOLD F/O, 'GO AROUND.' F/O EXECUTED SAME. TWR ADVISED. ISSUED 200 DEG HDG CLB TO 5000'. NEXT APCH TO SAME RWY COUPLED TO MINIMUMS IS UNEVENTFUL. DISCUSSED MATTER WITH AVIONICS MECH. SO FAR UNABLE TO ASCERTAIN WHY AUTOPLT APCH MODE COULD NOT BE REENGAGED NOR WHY ACFT WAS OFF COURSE TO RIGHT AT MINIMUMS.

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.