Narrative:

We were on an IFR flight plan; on a visual approach to runway 34; on a wide left base to final. I was using the ILS as a backup to the visual approach. I inappropriately armed the approach mode instead of the localizer mode; and when the glide slope needle started descending; I followed the flight director commands to descend.my copilot protested that something was wrong; and that I should not be descending any lower considering we were now at 800 feet AGL while still 5 miles from the runway. Immediately thereafter the control tower called and asked about our altitude.I immediately climbed back up to 1;500 feet AGL.we did not receive a traffic alert warning system (taws) alert.after landing we discussed that the flight director must have captured a false glide slope; and that I should not have armed the approach mode before being established on the localizer.I believe that a contributing factor was complacency due to the visual conditions.

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Original NASA ASRS Text

Title: FA10 flight crew reported descending to 800 feet AGL on a visual approach to FTW when the pilot flying followed a false glideslope.

Narrative: We were on an IFR flight plan; on a visual approach to runway 34; on a wide left base to final. I was using the ILS as a backup to the visual approach. I inappropriately armed the approach mode instead of the localizer mode; and when the glide slope needle started descending; I followed the flight director commands to descend.My copilot protested that something was wrong; and that I should not be descending any lower considering we were now at 800 feet AGL while still 5 miles from the runway. Immediately thereafter the control tower called and asked about our altitude.I immediately climbed back up to 1;500 feet AGL.We did not receive a Traffic Alert Warning System (TAWS) alert.After landing we discussed that the flight director must have captured a false glide slope; and that I should not have armed the approach mode before being established on the localizer.I believe that a contributing factor was complacency due to the visual conditions.

Data retrieved from NASA's ASRS site 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.