ZDC controller experienced operational error at FL210 when issuing descent clearance to occupied alt...

Attributes
ACN	824380
Time
Date	200902
Local Time Of Day	1201-1800
Place
Locale Reference	ZDC.ARTCC
State Reference	VA
Aircraft 1
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	Other
Operating Under FAR Part	Part 135
Flight Phase	Initial Approach
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 8
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict
Miss Distance	Horizontal 7020 Vertical 700

Narrative:

Aircraft #1 was a dca arrival that needed to be descended for traffic; and so I issued a descent to FL210. Aircraft #2 was additional traffic at FL210 that I missed. When I realized that aircraft #2 was a factor; I told aircraft #1 to amend the altitude to FL220; but they had already gone through FL220. They went to FL217 and climbed back up to FL220. I got completely fixated on traffic in the northern part of the sector I was working. I tunneled so much on the need to descend aircraft #1 that I failed to see traffic to the right of aircraft #1.

Original NASA ASRS Text

Title: ZDC Controller experienced operational error at FL210 when issuing descent clearance to occupied altitude; failing to note conflicting traffic; corrective action was too late.

Narrative: Aircraft #1 was a DCA arrival that needed to be descended for traffic; and so I issued a descent to FL210. Aircraft #2 was additional traffic at FL210 that I missed. When I realized that Aircraft #2 was a factor; I told Aircraft #1 to amend the altitude to FL220; but they had already gone through FL220. They went to FL217 and climbed back up to FL220. I got completely fixated on traffic in the northern part of the sector I was working. I tunneled so much on the need to descend Aircraft #1 that I failed to see traffic to the right of Aircraft #1.

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.

ZDC controller experienced operational error at FL210 when issuing descent clearance to occupied altitude; failing to note conflicting traffic; corrective action was too late.