Narrative:

Upon arriving into the nashville TRSA; heavy thunderstorms moving south near and around destination airport. Requested an ILS at bna and was told unable due to WX. Bna was not accepting flts. I stayed my original course which took me just north of the storm cells. I advised that I was apprehensive about the conditions at destination (M33). Approach solicited a ride report from aircraft in the vicinity. Smooth ride and moderate to heavy precipitation. I advised that I would shoot the straight-in GPS 35 approach and was cleared to the IAF. Upon reaching the fix; I started my descent in turbulent conditions and keeping control of the airplane was very difficult. Keeping a consistent descent rate was almost impossible. At times I felt like I could lose control of the aircraft. I resisted panic; but just barely. I was aware of my altitude at the time; but failed to realize I had confused the MDA of the previous fix with the upcoming fix; hence I had descended too low; too fast. I had descended to 1500 ft while the MDA was 2300 ft for this leg of the approach. This was noticed by the approach controller who canceled my clearance and instructed me to climb. He advised I was in danger of striking obstructions. I began to climb; while he read a fairly large amount of instructions; which I only heard about half of. I admitted to him that with everything that had just happened that I was a little overwhelmed right now. He calmly just gave me a heading to fly. I gathered myself and caught back up with the airplane. I was vectored to another airport with better conditions and made another GPS approach to a safe landing. The controller was very professional; and his calm demeanor was actually soothing and helped calm me down. He helped bail me out of a potentially fatal situation. I will be forever grateful. After I canceled my IFR with FSS; the controller was kind enough to call the airport where I landed to ask if I was ok. He could tell I was shaken by the way the events had unfolded. I apologized for making his day harder than it needed to be. Generally unstable WX in the area; low visibility and precipitation; all at the end of a long cross country of which the last hour was in IMC; was the stage for this poorly executed approach. Fatigue; coupled with fear and fixation on keeping the plane level and on course is where the very small detail of correct altitude was lost. It is possible that the only thing that makes this a NASA report and not an NTSB report was a very alert and very helpful approach controller. I'll be taking a BFR before I fly any more GPS approachs.

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Original NASA ASRS Text

Title: C182 DESCENDED BELOW PRESCRIBED ALTITUDE FOR APPROACH WHILE ENCOUNTERING TURBULENCE. ATC INSTRUCTED PLT TO CLIMB AND VECTORED TO ANOTHER ARPT.

Narrative: UPON ARRIVING INTO THE NASHVILLE TRSA; HVY TSTMS MOVING S NEAR AND AROUND DEST ARPT. REQUESTED AN ILS AT BNA AND WAS TOLD UNABLE DUE TO WX. BNA WAS NOT ACCEPTING FLTS. I STAYED MY ORIGINAL COURSE WHICH TOOK ME JUST N OF THE STORM CELLS. I ADVISED THAT I WAS APPREHENSIVE ABOUT THE CONDITIONS AT DEST (M33). APCH SOLICITED A RIDE RPT FROM ACFT IN THE VICINITY. SMOOTH RIDE AND MODERATE TO HVY PRECIP. I ADVISED THAT I WOULD SHOOT THE STRAIGHT-IN GPS 35 APCH AND WAS CLRED TO THE IAF. UPON REACHING THE FIX; I STARTED MY DSCNT IN TURBULENT CONDITIONS AND KEEPING CTL OF THE AIRPLANE WAS VERY DIFFICULT. KEEPING A CONSISTENT DSCNT RATE WAS ALMOST IMPOSSIBLE. AT TIMES I FELT LIKE I COULD LOSE CTL OF THE ACFT. I RESISTED PANIC; BUT JUST BARELY. I WAS AWARE OF MY ALT AT THE TIME; BUT FAILED TO REALIZE I HAD CONFUSED THE MDA OF THE PREVIOUS FIX WITH THE UPCOMING FIX; HENCE I HAD DSNDED TOO LOW; TOO FAST. I HAD DSNDED TO 1500 FT WHILE THE MDA WAS 2300 FT FOR THIS LEG OF THE APCH. THIS WAS NOTICED BY THE APCH CTLR WHO CANCELED MY CLRNC AND INSTRUCTED ME TO CLB. HE ADVISED I WAS IN DANGER OF STRIKING OBSTRUCTIONS. I BEGAN TO CLB; WHILE HE READ A FAIRLY LARGE AMOUNT OF INSTRUCTIONS; WHICH I ONLY HEARD ABOUT HALF OF. I ADMITTED TO HIM THAT WITH EVERYTHING THAT HAD JUST HAPPENED THAT I WAS A LITTLE OVERWHELMED RIGHT NOW. HE CALMLY JUST GAVE ME A HDG TO FLY. I GATHERED MYSELF AND CAUGHT BACK UP WITH THE AIRPLANE. I WAS VECTORED TO ANOTHER ARPT WITH BETTER CONDITIONS AND MADE ANOTHER GPS APCH TO A SAFE LNDG. THE CTLR WAS VERY PROFESSIONAL; AND HIS CALM DEMEANOR WAS ACTUALLY SOOTHING AND HELPED CALM ME DOWN. HE HELPED BAIL ME OUT OF A POTENTIALLY FATAL SITUATION. I WILL BE FOREVER GRATEFUL. AFTER I CANCELED MY IFR WITH FSS; THE CTLR WAS KIND ENOUGH TO CALL THE ARPT WHERE I LANDED TO ASK IF I WAS OK. HE COULD TELL I WAS SHAKEN BY THE WAY THE EVENTS HAD UNFOLDED. I APOLOGIZED FOR MAKING HIS DAY HARDER THAN IT NEEDED TO BE. GENERALLY UNSTABLE WX IN THE AREA; LOW VISIBILITY AND PRECIP; ALL AT THE END OF A LONG XCOUNTRY OF WHICH THE LAST HR WAS IN IMC; WAS THE STAGE FOR THIS POORLY EXECUTED APCH. FATIGUE; COUPLED WITH FEAR AND FIXATION ON KEEPING THE PLANE LEVEL AND ON COURSE IS WHERE THE VERY SMALL DETAIL OF CORRECT ALT WAS LOST. IT IS POSSIBLE THAT THE ONLY THING THAT MAKES THIS A NASA RPT AND NOT AN NTSB RPT WAS A VERY ALERT AND VERY HELPFUL APCH CTLR. I'LL BE TAKING A BFR BEFORE I FLY ANY MORE GPS APCHS.

Data retrieved from NASA's ASRS site as of January 2009 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.