Narrative:

While climbing through 10;000 feet; in a beechcraft king air 200; I 'thought' I was assigned FL230 and read-back FL230. I fly single-pilot so I reached over and set FL230 in my altitude alerter/pre-selector. Climbing through FL180 I completed the climb check and set both altimeters to 29.92. Approaching FL200 I saw traffic on my TCAS that was no factor to me as they were several miles to my south and traveling away from me 1000 feet above me; but nevertheless; in the name of safety; it prompted me to ask center if they could confirm an assigned altitude of FL230 for me. Center replied and asked me to stop my climb and maintain FL200. I promptly stopped my climb and leveled at FL200. A couple of minutes later I was; once again; given FL230. Later in the flight I was given the number for center; to call when I landed. I called and spoke with center and I was informed that I may have been involved with a possible altitude deviation. They also said I was given FL200 and that I read-back FL200. I have not heard this recording and cannot say for sure; one-way or another; if I read-back FL200 or FL230.another factor worth considering is altimeter error. I was told I deviated from my assigned FL200 by 400-500 feet; though on my altimeter I did not show that. As in many things in aviation; I think this minor event was the culmination of multiple factors. The controller who was working the sector during this event spoke clearly and was proficient in my opinion. I believe it was my mistake coupled with minor altimeter error; but regardless; I want to own my mistake and learn from it. I have 4500 hours and to my knowledge; I have never had any event like this or any other mishap. I am; however; human and I do fly single-pilot; so I think it is possible for me to make a mistake. I would like to say that; I truly thought I was climbing to FL230 and the only reason I spoke-up to ask ATC to confirm that assigned altitude was in the name of safety. I pride myself on professionalism and use all things at my disposal to help assure safety for myself and others. I will use this experience to make me better and safer. I apologize to anyone inconvenienced due to the event. I think ATC and the FAA do a great job protecting aviators and passengers alike; so I do respect the system and the people who execute it. I plan on re-focusing myself on preparation; verbal call-outs and read-backs (even in single-pilot operations). I plan on using this event to add another layer of useful experience and to make me better and safer as I continue my career.

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Original NASA ASRS Text

Title: King Air 200 pilot reported being cleared to FL230 and questioned the clearance approaching FL200 due to nearby traffic. ATC issued a level off at FL200 and stated that FL200 had been the original assignment.

Narrative: While climbing through 10;000 feet; in a Beechcraft King Air 200; I 'thought' I was assigned FL230 and read-back FL230. I fly single-pilot so I reached over and set FL230 in my altitude alerter/pre-selector. Climbing through FL180 I completed the Climb Check and set both altimeters to 29.92. Approaching FL200 I saw traffic on my TCAS that was no factor to me as they were several miles to my south and traveling away from me 1000 feet above me; but nevertheless; in the name of safety; it prompted me to ask Center if they could confirm an assigned altitude of FL230 for me. Center replied and asked me to stop my climb and maintain FL200. I promptly stopped my climb and leveled at FL200. A couple of minutes later I was; once again; given FL230. Later in the flight I was given the number for Center; to call when I landed. I called and spoke with Center and I was informed that I may have been involved with a possible altitude deviation. They also said I was given FL200 and that I read-back FL200. I have not heard this recording and cannot say for sure; one-way or another; if I read-back FL200 or FL230.Another factor worth considering is altimeter error. I was told I deviated from my assigned FL200 by 400-500 feet; though on my altimeter I did not show that. As in many things in aviation; I think this minor event was the culmination of multiple factors. The controller who was working the sector during this event spoke clearly and was proficient in my opinion. I believe it was my mistake coupled with minor altimeter error; but regardless; I want to own my mistake and learn from it. I have 4500 hours and to my knowledge; I have never had any event like this or any other mishap. I am; however; human and I do fly single-pilot; so I think it is possible for me to make a mistake. I would like to say that; I truly thought I was climbing to FL230 and the only reason I spoke-up to ask ATC to confirm that assigned altitude was in the name of safety. I pride myself on professionalism and use all things at my disposal to help assure safety for myself and others. I will use this experience to make me better and safer. I apologize to anyone inconvenienced due to the event. I think ATC and the FAA do a great job protecting aviators and passengers alike; so I do respect the system and the people who execute it. I plan on re-focusing myself on preparation; verbal call-outs and read-backs (even in single-pilot operations). I plan on using this event to add another layer of useful experience and to make me better and safer as I continue my career.

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.