Narrative:

At FL220 while using the autopilot; I encountered moderate icing in stratocumulus clouds (-25 degrees) at cruise enroute to ZZZ. I had been in the icing conditions less than a minute; but the windshields were icing over despite windshield heat being on. I asked and received clearance for a lower altitude. Concurrent with ATC's instructions; the deice boots caution message illuminated on the cas. The cas message indicates a failure in deice boots inflation system; and since I was carrying a significant amount of ice; the message divided my attention from ATC's instructions. After determining the state of the boots; which appeared to be working; I saw that I had set 7000 in the altitude preselect; but did not recall doing so or acknowledging the action. I called ATC and asked them to confirm my assigned altitude of 7000. I heard him say 6000 and repeated that instruction back to him; then set the altitude preselect for 6000.I am now approaching my destination which has its ASOS notamed out of service; but is transmitting weather info in the 'test' mode. I am looking at the ground where I believe my destination is and confirm that the ASOS is likely correct; 1/4 and VV100. My alternate is VFR and I am beginning to consider what changes I need to accommodate the new destination. Simultaneously; I get a TAS and a call from ATC telling me I was supposed to stop at 7000 and to climb. I saw a high-wing cessna at my 10 o'clock and about a mile and probably at 6000. I was at about 6300 when I began climbing. There was no danger of collision; but certainly a loss of separation. I climbed back to 7000 and finished the flight without further incident.in analysis of what went wrong; I cannot be sure if I misheard the controller; or if or he misheard me; or if the wrong instruction was given. It also seemed like a controller change occurred; but I am not sure. Clearly I was distracted; but only by operationally necessary tasks (looking for ZZZ; troubleshooting the boots; assessing ice distribution; alternate preparations; etc.); and I had relaxed my attention with regard to the assigned altitude; but I was aware that I was approaching the level-off. To my knowledge the autopilot was properly set and would perform according; but obviously it was not set correctly. In the future; I will be sure to doubly sure to confirm instructions with ATC when I recognize that my workload is divided between navigating the aircraft and systems. I believe this situation was a result of several near simultaneous incidents in a single pilot cockpit causing divided attention that contributed to a missed altitude and loss of separation.

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Original NASA ASRS Text

Title: PC-12 pilot reported descending through his cleared altitude when he was distracted by a problem with his de-ice boots.

Narrative: At FL220 while using the autopilot; I encountered moderate icing in stratocumulus clouds (-25 degrees) at cruise enroute to ZZZ. I had been in the icing conditions less than a minute; but the windshields were icing over despite windshield heat being ON. I asked and received clearance for a lower altitude. Concurrent with ATC's instructions; the DEICE BOOTS caution message illuminated on the CAS. The CAS message indicates a failure in deice boots inflation system; and since I was carrying a significant amount of ice; the message divided my attention from ATC's instructions. After determining the state of the boots; which appeared to be working; I saw that I had set 7000 in the altitude preselect; but did not recall doing so or acknowledging the action. I called ATC and asked them to confirm my assigned altitude of 7000. I heard him say 6000 and repeated that instruction back to him; then set the altitude preselect for 6000.I am now approaching my destination which has its ASOS NOTAMed out of service; but is transmitting weather info in the 'TEST' mode. I am looking at the ground where I believe my destination is and confirm that the ASOS is likely correct; 1/4 and VV100. My alternate is VFR and I am beginning to consider what changes I need to accommodate the new destination. Simultaneously; I get a TAS and a call from ATC telling me I was supposed to stop at 7000 and to climb. I saw a high-wing Cessna at my 10 o'clock and about a mile and probably at 6000. I was at about 6300 when I began climbing. There was no danger of collision; but certainly a loss of separation. I climbed back to 7000 and finished the flight without further incident.In analysis of what went wrong; I cannot be sure if I misheard the controller; or if or he misheard me; or if the wrong instruction was given. It also seemed like a controller change occurred; but I am not sure. Clearly I was distracted; but only by operationally necessary tasks (looking for ZZZ; troubleshooting the boots; assessing ice distribution; alternate preparations; etc.); and I had relaxed my attention with regard to the assigned altitude; but I was aware that I was approaching the level-off. To my knowledge the autopilot was properly set and would perform according; but obviously it was not set correctly. In the future; I will be sure to doubly sure to confirm instructions with ATC when I recognize that my workload is divided between navigating the aircraft and systems. I believe this situation was a result of several near simultaneous incidents in a single pilot cockpit causing divided attention that contributed to a missed altitude and loss of separation.

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.