Narrative:

I was working 2 aircraft that were involved in a possible operational error/pilot deviation. The call signs were air carrier X and air carrier Y. Air carrier Y checked on leaving FL200 climbing to FL230. The aircraft was instructed to maintain FL200. His response: 'leveling at 200.' I then asked air carrier X to verify leaving FL210. His reply was, 'roger, leaving 210 for 260.' I had therefore established 1000' vertical sep. 2 radar hits later air carrier Y's altitude read FL204. I asked the aircraft to verify level at FL200. His response was, 'yeah, we're level. We overshot a bit; we're gettin' back to it.' I was then removed from the radar position and the investigation began into the operational error/pilot deviation.

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Original NASA ASRS Text

Title: ACR Y HAD LESS THAN STANDARD SEPARATION FROM ACR X. SYSTEM ERROR.

Narrative: I WAS WORKING 2 ACFT THAT WERE INVOLVED IN A POSSIBLE OPERROR/PLTDEV. THE CALL SIGNS WERE ACR X AND ACR Y. ACR Y CHKED ON LEAVING FL200 CLBING TO FL230. THE ACFT WAS INSTRUCTED TO MAINTAIN FL200. HIS RESPONSE: 'LEVELING AT 200.' I THEN ASKED ACR X TO VERIFY LEAVING FL210. HIS REPLY WAS, 'ROGER, LEAVING 210 FOR 260.' I HAD THEREFORE ESTABLISHED 1000' VERT SEP. 2 RADAR HITS LATER ACR Y'S ALT READ FL204. I ASKED THE ACFT TO VERIFY LEVEL AT FL200. HIS RESPONSE WAS, 'YEAH, WE'RE LEVEL. WE OVERSHOT A BIT; WE'RE GETTIN' BACK TO IT.' I WAS THEN REMOVED FROM THE RADAR POS AND THE INVESTIGATION BEGAN INTO THE OPERROR/PLT DEV.

Data retrieved from NASA's ASRS site as of August 2007 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.