Date: 201708
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Super King Air 200
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Corporate
Reporter function: Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Communication Breakdown
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Conflict Airborne Conflict; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

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.




Synopsis: 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.