Narrative:

Misunderstanding of communications found the airplane at an altitude not expected by the controller. I had planned an IFR flight to ZZZ; but wanted to perform a high altitude pressurization test at FL270 in the area before heading for ZZZ. I filed a routine IFR flight plan and while picking up the clearance discussed the 'special request' with the clearance delivery controller. My understanding from the conversation was that he would coordinate with the approach and center controllers. I was released and vectored to the north at my initial altitude of 3000 feet. I was then given at or below 3500 feet due to conflicting traffic given a vector (after a brief interaction about on-course heading.) at this point I was handed off to center. When I checked in with center; I stated that I was at 3500 feet and 'heading for 270'. The controller cleared me to 270.(this is where the divergence of expectation probably arose.) I continued flying north and initiated my climb towards FL270 and heard nothing from the controller again until I reached about FL220 when an aircraft was overtaking me in the vicinity and he asked me what I was doing at that altitude. I was instructed to immediately descend below 18;000 feet at 17;999 feet to maintain VFR; I questioned this and suggested that I would be better at 17;000 feet and upon further clarification I was requested to fly at 17;500 feet.the controller made a number of comments to other aircraft that he had a VFR aircraft in IFR airspace. I descended as instructed; I was given a phone number to call to discuss with a supervisor when I landed; and after some back and forth was given routing and instructions for the flight to destination which continued uneventfully.I believe that the confusion must have occurred because I understood that I was on an IFR flight and was anticipating the climb to FL270 and the controller was not. I believed that the controller had heard about my intentions from the ground controller following the discussion I had with him. I was surprised by the direct climb to FL270 because normally there would be some intermediate stops; but assumed that because this was a check flight; the current controller was going to handle the flight directly. Hearing nothing more from the controller I assumed I was still following the last clearance. In retrospect; what the controller might have cleared me for was a turn to a heading of 270 and not an altitude of FL270. He was expecting a turn and I was expecting a climb; but this is only a guess since I didn't hear anything for about 6 minutes. Moving forward I will be sure to clarify all expectations with the every controller along the flight when performing 'non-standard' flights such as this. I will also be clearer on the flight intentions with the controllers before starting the flight.

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Original NASA ASRS Text

Title: PA46 pilot reported filing an IFR flight plan with a plan to climb to FL270 enroute for a pressurization check. At some point the IFR part of the flight plan was deleted and a heading of 270 was interpreted as a climb to FL270. The misunderstanding was not detected by ATC until the reporter was climbing through FL220.

Narrative: Misunderstanding of communications found the airplane at an altitude not expected by the controller. I had planned an IFR flight to ZZZ; but wanted to perform a high altitude pressurization test at FL270 in the area before heading for ZZZ. I filed a routine IFR flight plan and while picking up the clearance discussed the 'special request' with the clearance delivery controller. My understanding from the conversation was that he would coordinate with the approach and center controllers. I was released and vectored to the north at my initial altitude of 3000 feet. I was then given at or below 3500 feet due to conflicting traffic given a vector (after a brief interaction about on-course heading.) At this point I was handed off to center. When I checked in with center; I stated that I was at 3500 feet and 'heading for 270'. The controller cleared me to 270.(This is where the divergence of expectation probably arose.) I continued flying north and initiated my climb towards FL270 and heard nothing from the controller again until I reached about FL220 when an aircraft was overtaking me in the vicinity and he asked me what I was doing at that altitude. I was instructed to immediately descend below 18;000 feet at 17;999 feet to maintain VFR; I questioned this and suggested that I would be better at 17;000 feet and upon further clarification I was requested to fly at 17;500 feet.The controller made a number of comments to other aircraft that he had a VFR aircraft in IFR airspace. I descended as instructed; I was given a phone number to call to discuss with a supervisor when I landed; and after some back and forth was given routing and instructions for the flight to destination which continued uneventfully.I believe that the confusion must have occurred because I understood that I was on an IFR flight and was anticipating the climb to FL270 and the controller was not. I believed that the controller had heard about my intentions from the ground controller following the discussion I had with him. I was surprised by the direct climb to FL270 because normally there would be some intermediate stops; but assumed that because this was a check flight; the current controller was going to handle the flight directly. Hearing nothing more from the controller I assumed I was still following the last clearance. In retrospect; what the controller might have cleared me for was a turn to a heading of 270 and not an altitude of FL270. He was expecting a turn and I was expecting a climb; but this is only a guess since I didn't hear anything for about 6 minutes. Moving forward I will be sure to clarify all expectations with the every controller along the flight when performing 'non-standard' flights such as this. I will also be clearer on the flight intentions with the controllers before starting the flight.

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.