Narrative:

Aircraft #1 was issued a descent from FL410 to FL390 in the vicinity of katzn intersection. Aircraft #1 was observed descending through FL380 north of sawed intersection. Aircraft #1 was advised FL390 was his assigned altitude. The pilot apologized and said he was climbing back up to FL390. Aircraft #1 was advised of aircraft #2 beneath him and of a possible pilot deviation.

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Original NASA ASRS Text

Title: B757 AND AN MD80 HAD LESS THAN LEGAL SEPARATION.

Narrative: ACFT #1 WAS ISSUED A DSCNT FROM FL410 TO FL390 IN THE VICINITY OF KATZN INTXN. ACFT #1 WAS OBSERVED DSNDING THROUGH FL380 N OF SAWED INTXN. ACFT #1 WAS ADVISED FL390 WAS HIS ASSIGNED ALT. THE PLT APOLOGIZED AND SAID HE WAS CLBING BACK UP TO FL390. ACFT #1 WAS ADVISED OF ACFT #2 BENEATH HIM AND OF A POSSIBLE PLTDEV.

Data retrieved from NASA's ASRS site as of July 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.