B757 and an MD80 had less than legal separation.

Attributes
ACN	423612
Time
Date	199812
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : swl
State Reference	MD
Altitude	msl bound lower : 38000 msl bound upper : 39000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Navigation In Use	Other
Flight Phase	cruise other descent other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Navigation In Use	Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : developmental pilot : commercial pilot : cfi
Experience	controller non radar : 4 controller radar : 1
ASRS Report	423612
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : clearance
Independent Detector	other controllera
Resolutory Action	other other
Consequence	Other
Miss Distance	horizontal : 14400 vertical : 1000
Supplementary
Air Traffic Incident	Pilot Deviation

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.

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.