Narrative:

I was told by ATC to descend to 6;000 feet prior to entering the MOA. ZZZ approach descended me to 3;000 feet. My heading was 160. I was told to maintain 3;000 and turn left to 060. I was depending on my autopilot to maintain my altitude and make the turn. The radio transmission from ZZZ was weak and barely audible. I tried to ascertain the problem with the radio by turning the volume up and down; tapping on the radio. (The air traffic manager [later] told me they had played back the tapes and they recognized that their transmissions were weak.) approach control said; 'what are you doing? Where are you going? What altitude are you supposed to be at?' I then noticed that my altitude was approx. 2;000 feet. I stopped the descent and asked ATC; 'what do you want me to do?' ATC gave me a left turn to 40 degrees; then a right turn to base leg; and then a right turn to final which is on a heading of 240. I had been cleared to land; but at this point I was too high to land. I told the tower that I would either have to go around or make a 360 turn to lose altitude. The tower gave me a 360 degree turn to the right and told me to re enter a base leg. When I completed the turn the tower said I was not cleared to land. The tower told me to fly outbound on the right side of the outbound course and make a left turn back on to the final approach course to runway xx. Then I was cleared to land. When I landed the tower said to me possible deviation and asked me to call them by telephone. By telephone call I was told that I had busted the assigned altitude and had come within 100 feet of a king air and they would turn the information over to flight standard district office because of a loss of separation. How the problem arose: my auto pilot that was holding altitude apparently disengaged and I didn't hear the warning tone. I was preoccupied with the radio problem. Approach did not notify me of the unauthorized change in altitude until I was at 2200 feet.ways to prevent this problem in the future:the auto pilot warning sound should be louder. The pilot should scan the instruments even when dealing with other tasks; like checking into a radio problem. ATC should have their transmission equipment working so that their transmissions are clear and loud enough. ATC should have notified me of the unauthorized altitude change sooner.

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Original NASA ASRS Text

Title: A BE35 pilot suffered a NMAC in IMC when he failed to level at 3000 MSL as cleared by approach control.

Narrative: I was told by ATC to descend to 6;000 feet prior to entering the MOA. ZZZ approach descended me to 3;000 feet. My heading was 160. I was told to maintain 3;000 and turn left to 060. I was depending on my autopilot to maintain my altitude and make the turn. The radio transmission from ZZZ was weak and barely audible. I tried to ascertain the problem with the radio by turning the volume up and down; tapping on the radio. (The Air Traffic Manager [later] told me they had played back the tapes and they recognized that their transmissions were weak.) Approach Control said; 'What are you doing? Where are you going? What altitude are you supposed to be at?' I then noticed that my altitude was approx. 2;000 feet. I stopped the descent and asked ATC; 'What do you want me to do?' ATC gave me a left turn to 40 degrees; then a right turn to base leg; and then a right turn to final which is on a heading of 240. I had been cleared to land; but at this point I was too high to land. I told the Tower that I would either have to go around or make a 360 turn to lose altitude. The Tower gave me a 360 degree turn to the right and told me to re enter a base leg. When I completed the turn the Tower said I was not cleared to land. The Tower told me to fly outbound on the right side of the outbound course and make a left turn back on to the final approach course to Runway XX. Then I was cleared to land. When I landed the Tower said to me Possible Deviation and asked me to call them by telephone. By telephone call I was told that I had busted the assigned altitude and had come within 100 feet of a King Air and they would turn the information over to Flight Standard District Office because of a loss of separation. How the problem arose: My auto pilot that was holding altitude apparently disengaged and I didn't hear the warning tone. I was preoccupied with the radio problem. Approach did not notify me of the unauthorized change in altitude until I was at 2200 feet.Ways to prevent this problem in the future:The auto pilot warning sound should be louder. The pilot should scan the instruments even when dealing with other tasks; like checking into a radio problem. ATC should have their transmission equipment working so that their transmissions are clear and loud enough. ATC should have notified me of the unauthorized altitude change sooner.

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.