Narrative:

My student; his friend and I departed ZZZ on a night IFR training flight at xa:00 local time. An IFR flight plan was filed; clearance was received; and our route took us to ZZZ2 and ZZZ3 in that order. We shot two uneventful approaches at each airport and turned back towards ZZZ. The weather had been hard IMC earlier in the day with scattered showers; limited visibility; and low ceilings. However; it had improved during our flight. As we approached ZZZ; we asked for and received vectors from approach for the NDB xxr approach. As we joined the final approach course; approximately 7-10 NM from the airport; approach informed us they would be closing momentarily. They asked us to close our flight plan as soon as practical or we would have to be handed off to center. I was adamant that we not close because I did not have the field in sight. I could see the layer of clouds at 500 ft hanging just over the approximate position of our airfield.as we passed the FAF; 3.7 NM from the runway; just as I was hoping to be handed off to CTAF; approach told us to switch to ZZZ center. We switched to center's frequency and were immediately asked again to close our flight plan. My student also asked me a question at this point. I can't even remember what he asked me. I told him we were entering the cloud layer and that he needed to concentrate on the approach. I told center that we still didn't have the field in sight.a very short time later we descended through the bottom of the clouds to find the airport at our xj:30 position about 1 NM away. I immediately reported the field in sight and closed the flight plan with center. This is when I realized our altitude was approximately 1;150 ft MSL. Field elevation at ZZZ is 952 ft MSL! In a fairly startled tone I told my student to pull up and reacquire runway centerline. I also looked down at my approach plate to discover that our minimums were 1;480 ft MSL (552 ft AGL). After regaining altitude we landed uneventfully; but at no time did we even make a transmission on the CTAF.I believe there are several contributing factors to this incident. I violated my own personal; standing checklist: 1. Aviate 2. Navigate 3. Communicate. I was so tied up with ATC I was barely paying any attention to my student's flight path. His approach briefings have always been complete; but he talks through them very quickly. It didn't even register that our MDA; if held properly; would have put us right in the middle of the cloud layer. Seeing the obscured field several miles out; I should have requested a frequency change to the CTAF even before the FAF which would have alleviated much of the communication that occurred.fatigue also played a factor. Although I didn't feel tired at the time; I had been awake since xu:00. I can only hypothesize that my student had some trouble tracking the bearing pointer on the HSI. He had not used such a nav-aid in a month or so. Having a good friend ride in the backseat also usually has some varied effects on student flying skills.lastly; in hindsight; I've realized that the approach we shot was not even legal because the cirrus sr-20 does not have an ADF. We put the NDB into the GPS and tracked it that way. I'm fairly certain that setup is illegal in IMC.

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Original NASA ASRS Text

Title: A CFII and his Student experienced a CFTT to 200 AGL while flying a night NDB approach to minimums. Repeated requests from ATC to cancel their flight plan distracted the Instructor from monitoring the aircraft's flight path.

Narrative: My student; his friend and I departed ZZZ on a night IFR training flight at XA:00 local time. An IFR flight plan was filed; clearance was received; and our route took us to ZZZ2 and ZZZ3 in that order. We shot two uneventful approaches at each airport and turned back towards ZZZ. The weather had been hard IMC earlier in the day with scattered showers; limited visibility; and low ceilings. However; it had improved during our flight. As we approached ZZZ; we asked for and received vectors from Approach for the NDB XXR approach. As we joined the final approach course; approximately 7-10 NM from the airport; Approach informed us they would be closing momentarily. They asked us to close our flight plan as soon as practical or we would have to be handed off to Center. I was adamant that we not close because I did not have the field in sight. I could see the layer of clouds at 500 FT hanging just over the approximate position of our airfield.As we passed the FAF; 3.7 NM from the runway; just as I was hoping to be handed off to CTAF; Approach told us to switch to ZZZ center. We switched to Center's frequency and were immediately asked again to close our flight plan. My student also asked me a question at this point. I can't even remember what he asked me. I told him we were entering the cloud layer and that he needed to concentrate on the approach. I told Center that we still didn't have the field in sight.A very short time later we descended through the bottom of the clouds to find the airport at our XJ:30 position about 1 NM away. I immediately reported the field in sight and closed the flight plan with Center. This is when I realized our altitude was approximately 1;150 FT MSL. Field elevation at ZZZ is 952 FT MSL! In a fairly startled tone I told my student to pull up and reacquire runway centerline. I also looked down at my approach plate to discover that our minimums were 1;480 FT MSL (552 FT AGL). After regaining altitude we landed uneventfully; but at no time did we even make a transmission on the CTAF.I believe there are several contributing factors to this incident. I violated my own personal; standing checklist: 1. Aviate 2. Navigate 3. Communicate. I was so tied up with ATC I was barely paying any attention to my student's flight path. His approach briefings have always been complete; but he talks through them very quickly. It didn't even register that our MDA; if held properly; would have put us right in the middle of the cloud layer. Seeing the obscured field several miles out; I should have requested a frequency change to the CTAF even before the FAF which would have alleviated much of the communication that occurred.Fatigue also played a factor. Although I didn't feel tired at the time; I had been awake since XU:00. I can only hypothesize that my student had some trouble tracking the bearing pointer on the HSI. He had not used such a nav-aid in a month or so. Having a good friend ride in the backseat also usually has some varied effects on student flying skills.Lastly; in hindsight; I've realized that the approach we shot was not even legal because the Cirrus SR-20 does not have an ADF. We put the NDB into the GPS and tracked it that way. I'm fairly certain that setup is illegal in IMC.

Data retrieved from NASA's ASRS site as of April 2012 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.