Narrative:

I was vectored in IMC at 9000 ft to the ILS 17L approach at cos by pueblo approach then switched to tower outside of awone. Ceiling at cos broadcast at 1500 overcast 1000 broken.I set up the garmin GNS 430 and navigation 2 (navigation 2) for the ILS 17L approach and noticed on the garmin obs (omni bearing selector) that the glideslope indicator was centered. Not realizing there was a problem I started down following what I thought was the glideslope.my problem; in hindsight was that I did not compare the garmin obs with the navigation 2 to verify they were agreeing with each other. I also did not double check my altitude compared to the intermediate fixes. I found that I broke out of the clouds at 120 AGL; much lower than expected. Also; I broke out too far away from the runway. Based on my research I believe one of two things occurred during my setup of the GNS 430. I either did not activate the ILS frequency 109.1 and/or did not verify that it switched from GPS to 'vloc'. As mentioned; I did not compare the two obs to determine consistency and did not verify location versus altitude. I did not receive a low altitude alert from tower; nor did I notice a terrain alert from the GNS 430. I am current with the necessary number of approaches and I wonder if the transition from a GPS environment to the occasional ILS/VOR environment causes confusion; especially in the heat of battle. I'm wondering if there may be some way to alter the functionality of future devices; or the training curriculum to help negate the inherent confusion to such a transition. I came back to the airport two days later to fly with a local CFI to help figure out what went awry. This along with my plans to go back up with my own instructor to refresh myself on proper techniques should help prevent this in the future.

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Original NASA ASRS Text

Title: GA pilot reported that he descended below the Decision Altitude in IMC due to improper instrument equipment setup procedures.

Narrative: I was vectored in IMC at 9000 FT to the ILS 17L approach at COS by Pueblo approach then switched to tower outside of AWONE. Ceiling at COS broadcast at 1500 overcast 1000 broken.I set up the Garmin GNS 430 and NAV 2 (Navigation 2) for the ILS 17L approach and noticed on the Garmin OBS (Omni Bearing Selector) that the glideslope indicator was centered. Not realizing there was a problem I started down following what I thought was the glideslope.My problem; in hindsight was that I did not compare the Garmin OBS with the NAV 2 to verify they were agreeing with each other. I also did not double check my altitude compared to the intermediate fixes. I found that I broke out of the clouds at 120 AGL; much lower than expected. Also; I broke out too far away from the runway. Based on my research I believe one of two things occurred during my setup of the GNS 430. I either did not activate the ILS frequency 109.1 and/or did not verify that it switched from GPS to 'VLOC'. As mentioned; I did not compare the two OBS to determine consistency and did not verify location versus altitude. I did not receive a low altitude alert from tower; nor did I notice a terrain alert from the GNS 430. I am current with the necessary number of approaches and I wonder if the transition from a GPS environment to the occasional ILS/VOR environment causes confusion; especially in the heat of battle. I'm wondering if there may be some way to alter the functionality of future devices; or the training curriculum to help negate the inherent confusion to such a transition. I came back to the airport two days later to fly with a local CFI to help figure out what went awry. This along with my plans to go back up with my own instructor to refresh myself on proper techniques should help prevent this in the future.

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.