Narrative:

I had routed around the atlanta class B airspace while penetrating an area of thunderstorms using visual; radar and nexrad. Requested climb from 9;000 to 10;000 to get above the tops and better judge appropriate deviation routes. I was also cleared to deviate left and right. I set 10;000 into altitude alert; put the autopilot in pitch mode and started climb.I was distracted by the need to make several turns to avoid visual and radar areas of heavy rain while in light to very heavy rain and turbulence. I recall seeing too high a pitch attitude and decreasing airspeed so rotated the pitch wheel down. I was so intent on staying out of the nasty stuff and finding a good way through that I forgot I was supposed to be climbing to 10;000. Approach called to confirm my altitude as 8;300 and asked why I was going down; not up. I told them I was in heavy turbulence and having trouble holding altitude. The autopilot did not disconnect in the bumps. I simply got distracted trying to get through the weather. I re-initiated by climb to 10;000. Approach said there was lower traffic; but was out of the way. Single pilot piston twin; in and out of heavy rain in southeast afternoon thunderstorms; in and out of IMC and worried about a passenger is a full work load. My last real IMC thunderstorm experience was several years ago. The more successful you are at staying out of thunderstorms the less proficient you are at getting through them. My autopilot does not have an altitude preselect which would have avoided the problem. I thought about disconnecting and hand flying; but managing the turns to avoid with radar and nexrad and the occasional VFR peek took a lot of attention. In hindsight I could have deviated 20 miles north and had a less stressful flight.

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Original NASA ASRS Text

Title: An Aerostar 601P single pilot reported difficulties experienced when attempting to avoid thunderstorms and turbulence while circumnavigating the ATL Class B airspace.

Narrative: I had routed around the Atlanta Class B airspace while penetrating an area of thunderstorms using visual; radar and Nexrad. Requested climb from 9;000 to 10;000 to get above the tops and better judge appropriate deviation routes. I was also cleared to deviate left and right. I set 10;000 into Altitude Alert; put the autopilot in pitch mode and started climb.I was distracted by the need to make several turns to avoid visual and radar areas of heavy rain while in light to very heavy rain and turbulence. I recall seeing too high a pitch attitude and decreasing airspeed so rotated the pitch wheel down. I was so intent on staying out of the nasty stuff and finding a good way through that I forgot I was supposed to be climbing to 10;000. Approach called to confirm my altitude as 8;300 and asked why I was going down; not up. I told them I was in heavy turbulence and having trouble holding altitude. The autopilot did not disconnect in the bumps. I simply got distracted trying to get through the weather. I re-initiated by climb to 10;000. Approach said there was lower traffic; but was out of the way. Single pilot piston twin; in and out of heavy rain in southeast afternoon thunderstorms; in and out of IMC and worried about a passenger is a full work load. My last real IMC thunderstorm experience was several years ago. The more successful you are at staying out of thunderstorms the less proficient you are at getting through them. My autopilot does not have an altitude preselect which would have avoided the problem. I thought about disconnecting and hand flying; but managing the turns to avoid with radar and Nexrad and the occasional VFR peek took a lot of attention. In hindsight I could have deviated 20 miles north and had a less stressful flight.

Data retrieved from NASA's ASRS site as of July 2013 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.