B727 at FL230 was instructed to cross fix at 13000 ft. When controller noticed the B727 at FL228, he cleared an MD80 to FL230. The controller then observed the B727 at FL231 and instructed the pilot to descend to 13000 ft. The MD80 had begun descent to FL230 and conflicted with the B727. Incident occurred in ZDC airspace.

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Attributes
ACN	400503
Time
Date	199804
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : dqo
State Reference	DE
Altitude	msl bound lower : 23000 msl bound upper : 23000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	common carrier : air carrier
Make Model Name	B727 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	enroute airway : zdc enroute other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Route In Use	enroute other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 10
ASRS Report	400503
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance none taken : detected after the fact
Consequence	Other
Miss Distance	horizontal : 25200 vertical : 800
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X B727 was given a clearance to cross a fix at 13000 ft. I noticed air carrier X in descent. Air carrier MD80 was given a clearance to descend to the altitude that air carrier X had vacated. Air carrier X left FL230, was seen at FL228 then climbed to FL231 before being told to continue descent thru FL220 to 13000 ft. Air carrier Y was told to stop descent.

Original NASA ASRS Text

Title: B727 AT FL230 WAS INSTRUCTED TO CROSS FIX AT 13000 FT. WHEN CTLR NOTICED THE B727 AT FL228, HE CLRED AN MD80 TO FL230. THE CTLR THEN OBSERVED THE B727 AT FL231 AND INSTRUCTED THE PLT TO DSND TO 13000 FT. THE MD80 HAD BEGUN DSCNT TO FL230 AND CONFLICTED WITH THE B727. INCIDENT OCCURRED IN ZDC AIRSPACE.

Narrative: ACR X B727 WAS GIVEN A CLRNC TO CROSS A FIX AT 13000 FT. I NOTICED ACR X IN DSCNT. ACR MD80 WAS GIVEN A CLRNC TO DSND TO THE ALT THAT ACR X HAD VACATED. ACR X LEFT FL230, WAS SEEN AT FL228 THEN CLBED TO FL231 BEFORE BEING TOLD TO CONTINUE DSCNT THRU FL220 TO 13000 FT. ACR Y WAS TOLD TO STOP DSCNT.

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.