Narrative:

Aircraft equipped with EFIS, autoplt #1 engaged, on vector to intercept localizer for an ILS approach with an airspeed requested by ATC of approximately 210 KTS and an altitude of approximately 3800 ft AGL. ILS was tuned and idented and 'land' selected. Both the commanding officer and first officer navigation display mode selectors were in 'map' and approach/VOR switches in 'approach.' ILS raw data was displayed on the pilot's flight display screens. The FMA showed a green localizer being captured and the command bars showed the commencement of a turn. At that time a 'VOR 1' flashing amber warning illuminated on the FMA. As the crew concentrated on what this was indicating and how to correct it. The autoplt flew the aircraft to the left of course. (A flashing amber 'VOR 1' light indicates the aircraft is not tracking a VOR 1 course. A flashing blue 'localizer' indicates the aircraft is not tracking the localizer course. Since 'VOR' was not selected the amber 'VOR 1' flashing light should be impossible. Follow up talks with our training department confirms this, and it's believed the problem was in the flight control computer). The autoplt was disconnected, and the aircraft was manually flown back to the localizer. Human performance considerations. Concentration by both pilots on the incongruity of the display shifted attention away from raw data, allowing the autoplt to fly the aircraft off course. Probable cause. Something in the flight control computer caused a spurious 'VOR 1' flashing amber warning to appear in the commanding officer's FMA.

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Original NASA ASRS Text

Title: MLG COMPUTER EQUIP GIVES ERRONEOUS VOR WARNING. WHILE CREW CONCENTRATES ON WARNING, AUTOPLT FLIES ACFT L OF COURSE.

Narrative: ACFT EQUIPPED WITH EFIS, AUTOPLT #1 ENGAGED, ON VECTOR TO INTERCEPT LOC FOR AN ILS APCH WITH AN AIRSPD REQUESTED BY ATC OF APPROX 210 KTS AND AN ALT OF APPROX 3800 FT AGL. ILS WAS TUNED AND IDENTED AND 'LAND' SELECTED. BOTH THE COMMANDING OFFICER AND FO NAV DISPLAY MODE SELECTORS WERE IN 'MAP' AND APCH/VOR SWITCHES IN 'APCH.' ILS RAW DATA WAS DISPLAYED ON THE PLT'S FLT DISPLAY SCREENS. THE FMA SHOWED A GREEN LOC BEING CAPTURED AND THE COMMAND BARS SHOWED THE COMMENCEMENT OF A TURN. AT THAT TIME A 'VOR 1' FLASHING AMBER WARNING ILLUMINATED ON THE FMA. AS THE CREW CONCENTRATED ON WHAT THIS WAS INDICATING AND HOW TO CORRECT IT. THE AUTOPLT FLEW THE ACFT TO THE L OF COURSE. (A FLASHING AMBER 'VOR 1' LIGHT INDICATES THE ACFT IS NOT TRACKING A VOR 1 COURSE. A FLASHING BLUE 'LOC' INDICATES THE ACFT IS NOT TRACKING THE LOC COURSE. SINCE 'VOR' WAS NOT SELECTED THE AMBER 'VOR 1' FLASHING LIGHT SHOULD BE IMPOSSIBLE. FOLLOW UP TALKS WITH OUR TRAINING DEPT CONFIRMS THIS, AND IT'S BELIEVED THE PROBLEM WAS IN THE FLT CTL COMPUTER). THE AUTOPLT WAS DISCONNECTED, AND THE ACFT WAS MANUALLY FLOWN BACK TO THE LOC. HUMAN PERFORMANCE CONSIDERATIONS. CONCENTRATION BY BOTH PLTS ON THE INCONGRUITY OF THE DISPLAY SHIFTED ATTN AWAY FROM RAW DATA, ALLOWING THE AUTOPLT TO FLY THE ACFT OFF COURSE. PROBABLE CAUSE. SOMETHING IN THE FLT CTL COMPUTER CAUSED A SPURIOUS 'VOR 1' FLASHING AMBER WARNING TO APPEAR IN THE COMMANDING OFFICER'S FMA.

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.