Narrative:

I am IFR current as required by fars. I had filed and had been given a direct IFR flight plan route at 5;000 feet. This C182 is equipped with a garmin GTN650 GPS and a bendix king kap 140 autopilot (without altitude pre-select). I encountered IMC with light to moderate precipitation with light turbulence...I noticed on the satellite xm weather display that heavier precipitation was directly in my path and asked for and was given by center a deviation to ZZZ. I tried; but was unable to receive AWOS from that airport. I set a direct-to route on the gamin GTN650 GPS and turned to a direct course to the airport. The autopilot was in altitude and nav modes. The ATC controller told me to descend to 2;500 feet; report the airport in sight. However; as I flew within 5 miles of the airport; I was still in IMC and could not see the airport. I asked for and received a clearance for RNAV GPS approach to runway xx... I was having trouble programming the garmin 650 GPS and finding touch selection for the initial approach fix so I could activate the approach to runway xx. The garmin GTN650 is different than the gamin 430w that I am used to. The gtn 650 is touch screen and menu selections are different. I set the autopilot to heading mode and turned to a southerly direction. Still unable to find the touch selection for the IAF; I activated the GPS approach in the default vectors mode. I intended to navigate manually and allow the autopilot intercept and track the approach. I turned to an intercept angle manually by turning off the autopilot. I turned the autopilot back on and thought I had pushed the altitude; but may have pressed the apr mode button. After a short period of time I noticed I had descended from 2;500 feet MSL to 1;500 feet MSL and was in a 30-40 degree bank. I turned the autopilot off and leveled the plane and then climbed to 2;000 feet. I called ATC and declared a missed approach. I told the controller that I would like to go to an airport that was reporting better weather. I also told him that I had about an hour of fuel left. He gave me a couple of options and vectors to other nearby airports. While trying to input the vectors into the GPS and set the autopilot I made at least one 180 turn. A different controller called and had me climb to 3;000 feet. He said that ZZZ2 was reporting marginal VFR and gave me vectors to the airport. It was not until about 3 miles from the airport that I came out of IMC and was able to see the airport. I landed safely though very shaken. I never told the controllers that I was having problems programming the gtn 650 GPS. However one controller did ask if I was instrument rated. The reason for this event was my total lack of understanding of newer garmin GTN650 GPS and allowing that fact to distract me from flying the aircraft safely. This resulted in an unintended descent of at least 1;000 feet; a bank angle of 30 to 40 degrees; and an 180 turn all while under IMC. This aircraft is a rental and I was checked out on it. However; I did not study the GTN650 GPS enough and did not fully understand its interactions with the autopilot. Needless to say I will never let this happen again and consider myself lucky!

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Original NASA ASRS Text

Title: Instrument qualified C182 pilot experienced track and altitude deviations on two attempted RNAV approaches in IMC due to lack of familiarity with the model of GPS installed. Pilot landed safely after vectors to an airport in VMC.

Narrative: I am IFR current as required by FARs. I had filed and had been given a direct IFR flight plan route at 5;000 feet. This C182 is equipped with a Garmin GTN650 GPS and a Bendix King KAP 140 autopilot (without altitude pre-select). I encountered IMC with light to moderate precipitation with light turbulence...I noticed on the satellite XM Weather display that heavier precipitation was directly in my path and asked for and was given by Center a deviation to ZZZ. I tried; but was unable to receive AWOS from that airport. I set a direct-to route on the Gamin GTN650 GPS and turned to a direct course to the airport. The autopilot was in Altitude and Nav modes. The ATC Controller told me to descend to 2;500 feet; report the airport in sight. However; as I flew within 5 miles of the airport; I was still in IMC and could not see the airport. I asked for and received a clearance for RNAV GPS Approach to Runway XX... I was having trouble programming the Garmin 650 GPS and finding touch selection for the initial approach fix so I could activate the approach to Runway XX. The Garmin GTN650 is different than the Gamin 430w that I am used to. The GTN 650 is touch screen and menu selections are different. I set the autopilot to heading mode and turned to a southerly direction. Still unable to find the touch selection for the IAF; I activated the GPS approach in the default Vectors mode. I intended to navigate manually and allow the autopilot intercept and track the approach. I turned to an intercept angle manually by turning off the autopilot. I turned the autopilot back on and thought I had pushed the ALT; but may have pressed the APR mode button. After a short period of time I noticed I had descended from 2;500 feet MSL to 1;500 feet MSL and was in a 30-40 degree bank. I turned the autopilot off and leveled the plane and then climbed to 2;000 feet. I called ATC and declared a missed approach. I told the Controller that I would like to go to an airport that was reporting better weather. I also told him that I had about an hour of fuel left. He gave me a couple of options and vectors to other nearby airports. While trying to input the vectors into the GPS and set the autopilot I made at least one 180 turn. A different Controller called and had me climb to 3;000 feet. He said that ZZZ2 was reporting marginal VFR and gave me vectors to the airport. It was not until about 3 miles from the airport that I came out of IMC and was able to see the airport. I landed safely though very shaken. I never told the controllers that I was having problems programming the GTN 650 GPS. However one Controller did ask if I was instrument rated. The reason for this event was my total lack of understanding of newer Garmin GTN650 GPS and allowing that fact to distract me from flying the aircraft safely. This resulted in an unintended descent of at least 1;000 feet; a bank angle of 30 to 40 degrees; and an 180 turn all while under IMC. This aircraft is a rental and I was checked out on it. However; I did not study the GTN650 GPS enough and did not fully understand its interactions with the autopilot. Needless to say I will never let this happen again and consider myself lucky!

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.