Narrative:

Aircraft X was on vectors for a localizer approach and was level at 15000. A citation jet was on vectors for same type of approach at 16000. As the citation jet was approaching aircraft X; the altitude for the citation jet was 160 and aircraft X was between 150 and 151. The manager asked if aircraft X was at 15000 or 15100. I said that he was assigned 15000. Aircraft X displayed 150 (15000) when the aircraft passed; but the citation jet indicated 159. They were assigned altitudes that were separated by 1000 feet; which is what was required. The manager said that 900 feet was not 1000 feet. Recommendation; I have worked radar for about fifteen years and this has never been an issue until today. The altitude readouts have always fluctuated a little; but I have never been told that I didn't have separation. My recommendation is that we use two thousand feet separation to eliminate this problem; or educate management personnel that this is not an issue.

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Original NASA ASRS Text

Title: Controller described event when manager questioned altitude separation of two aircraft indicating 900 feet of separation.

Narrative: Aircraft X was on vectors for a Localizer Approach and was level at 15000. A Citation Jet was on vectors for same type of approach at 16000. As the Citation Jet was approaching Aircraft X; the altitude for the Citation Jet was 160 and Aircraft X was between 150 and 151. The Manager asked if Aircraft X was at 15000 or 15100. I said that he was assigned 15000. Aircraft X displayed 150 (15000) when the aircraft passed; but the Citation Jet indicated 159. They were assigned altitudes that were separated by 1000 feet; which is what was required. The manager said that 900 feet was not 1000 feet. Recommendation; I have worked RADAR for about fifteen years and this has never been an issue until today. The altitude readouts have always fluctuated a little; but I have never been told that I didn't have separation. My recommendation is that we use two thousand feet separation to eliminate this problem; or educate management personnel that this is not an issue.

Data retrieved from NASA's ASRS site as of April 2012 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.