Narrative:

Heading 090 I was cleared descent at pilot's discretion from 9000' to 3000' through cumulus with tops to 11000' and faces about 5000'. At about 6500' received further descent clearance to 2000' with a traffic alert at 11 O'clock 12 mi northbound. I was still in the clouds. Upon reporting level at 2000' ATC called traffic at 10 O'clock one mi. An small aircraft was ahead, low and to the left moving in the same direction. I slowed to follow him assuming he was headed for marianna airport which I still hadn't been able to identify. I was still above and behind him when he did a chandelle to the left completely reversing his course. At the peak of his maneuver he was near my altitude less than a mi ahead. He did no clearing turn and probably never saw me. ATC called to remind me that my assigned altitude was 2000' that was when I realized I had descended to 1500' while slowing down and watching the small aircraft I climbed back to 2000' from a slow flight confign and idented the airport. VFR approach and landing went west/O incident. I must take the blame for an IFR altitude deviation in VMC because of distraction from a VFR traffic conflict. There were no obstruction hazards along my course however I did descend below an assigned altitude. This reflects on my plting abilities to handle distrs. Distrs can kill. This has left an impression on me which I hope will prevent another incident.

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Original NASA ASRS Text

Title: SMA PLT ON IFR FLT PLAN DESCENDS BELOW ASSIGNED ALT IN CLOSE PROX OF SMA DOING MANEUVERS.

Narrative: HDG 090 I WAS CLRED DSNT AT PLT'S DISCRETION FROM 9000' TO 3000' THROUGH CUMULUS WITH TOPS TO 11000' AND FACES ABOUT 5000'. AT ABOUT 6500' RECEIVED FURTHER DSCNT CLRNC TO 2000' WITH A TFC ALERT AT 11 O'CLOCK 12 MI NBND. I WAS STILL IN THE CLOUDS. UPON RPTING LEVEL AT 2000' ATC CALLED TFC AT 10 O'CLOCK ONE MI. AN SMA WAS AHEAD, LOW AND TO THE L MOVING IN THE SAME DIRECTION. I SLOWED TO FOLLOW HIM ASSUMING HE WAS HEADED FOR MARIANNA ARPT WHICH I STILL HADN'T BEEN ABLE TO IDENT. I WAS STILL ABOVE AND BEHIND HIM WHEN HE DID A CHANDELLE TO THE L COMPLETELY REVERSING HIS COURSE. AT THE PEAK OF HIS MANEUVER HE WAS NEAR MY ALT LESS THAN A MI AHEAD. HE DID NO CLRING TURN AND PROBABLY NEVER SAW ME. ATC CALLED TO REMIND ME THAT MY ASSIGNED ALT WAS 2000' THAT WAS WHEN I REALIZED I HAD DSNDED TO 1500' WHILE SLOWING DOWN AND WATCHING THE SMA I CLBED BACK TO 2000' FROM A SLOW FLT CONFIGN AND IDENTED THE ARPT. VFR APCH AND LNDG WENT W/O INCIDENT. I MUST TAKE THE BLAME FOR AN IFR ALT DEV IN VMC BECAUSE OF DISTR FROM A VFR TFC CONFLICT. THERE WERE NO OBSTRUCTION HAZARDS ALONG MY COURSE HOWEVER I DID DSND BELOW AN ASSIGNED ALT. THIS REFLECTS ON MY PLTING ABILITIES TO HANDLE DISTRS. DISTRS CAN KILL. THIS HAS LEFT AN IMPRESSION ON ME WHICH I HOPE WILL PREVENT ANOTHER INCIDENT.

Data retrieved from NASA's ASRS site as of July 2007 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.