Narrative:

Aircraft X departed. Aircraft X was on an IFR flight plan departing to the northeast. His final altitude requesting was 5;000 feet. I glanced at the flight strip and for some reason thought he was VFR requesting 5;500 feet. Aircraft Y was northeast; southwest bound; IFR at 4;000 feet. I knew the two aircraft would possibly be a factor for one another so I assigned aircraft X 3;500 feet for an altitude based on my wrong assumption that he was VFR. The two aircraft crossed about 2 miles from one another and slightly diverging at about 500 feet based on the altitude I had assigned. When the traffic was no longer a factor I tried to climb aircraft X to 5;500 feet and the pilot questioned the altitude and at that time I realized my mistake. I then assigned him the correct altitude of 5;000 feet. I had just taken the position from another controller and I believe I may have looked at the wrong flight strip and also I did not notice the data block not indicating VFR. I think I made a false assumption in my mind when the aircraft departed and never double checked. I think simply my lack of awareness led to the error. I was fully aware that the two aircraft needed to be separated and I took action but used wrong separation minima based on thinking that aircraft X was VFR. Be more aware of flight information on flight strips and data blocks. Also don't make assumptions about aircraft and their status. My scanning probably should have caught the error. Additionally when initially taking a control position be more aware that errors may occur.

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Original NASA ASRS Text

Title: A Controller thought an IFR aircraft was VFR. The Controller assigned the aircraft an altitude 500 feet below another IFR aircraft.

Narrative: Aircraft X departed. Aircraft X was on an IFR flight plan departing to the northeast. His final altitude requesting was 5;000 feet. I glanced at the flight strip and for some reason thought he was VFR requesting 5;500 feet. Aircraft Y was northeast; southwest bound; IFR at 4;000 feet. I knew the two aircraft would possibly be a factor for one another so I assigned Aircraft X 3;500 feet for an altitude based on my wrong assumption that he was VFR. The two aircraft crossed about 2 miles from one another and slightly diverging at about 500 feet based on the altitude I had assigned. When the traffic was no longer a factor I tried to climb Aircraft X to 5;500 feet and the pilot questioned the altitude and at that time I realized my mistake. I then assigned him the correct altitude of 5;000 feet. I had just taken the position from another controller and I believe I may have looked at the wrong flight strip and also I did not notice the data block not indicating VFR. I think I made a false assumption in my mind when the aircraft departed and never double checked. I think simply my lack of awareness led to the error. I was fully aware that the two aircraft needed to be separated and I took action but used wrong separation minima based on thinking that Aircraft X was VFR. Be more aware of flight information on flight strips and data blocks. Also don't make assumptions about aircraft and their status. My scanning probably should have caught the error. Additionally when initially taking a control position be more aware that errors may occur.

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.