ZDC misses MD80 readback and aircraft descends into conflict with level, en route B738.

Attributes
ACN	509832
Time
Date	200105
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : gso.vortac
State Reference	NC
Altitude	msl bound lower : 25000 msl bound upper : 25700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc.artcc
Operator	common carrier : air carrier
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zdc.artcc
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	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	509832
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment : conflict alert other controllera
Resolutory Action	controller : issued new clearance
Consequence	faa : investigated
Miss Distance	horizontal : 24372 vertical : 700
Supplementary
Problem Areas	ATC Facility ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error
Situations
ATC Facility	other physical facility

Narrative:

I was working 2 aircraft -- 1 landing iad, 1 landing bwi. The iad aircraft was at FL250 and faster and in front of the bwi aircraft. Turbulence was being reported at FL280-FL290. Normally bwi aircraft are descended to FL290 in my sector. I elected to descend the bwi to FL270 where the air was reported as smooth. I looked at the iad aircraft at FL250, then thought I issued the bwi aircraft FL270 from FL290. I actually said FL250. I noticed the bwi aircraft descending through FL270 and restated the assigned altitude of FL270 (which I thought I had issued). The aircraft then climbed back up to FL270 after descending down to FL257. The aircraft were no closer than 4 mi laterally and 700 ft vertically. Having to concentrate on issuing clrncs then hearing the readback is strenuous enough. The noise in the areas from people talking and joking around is making that even harder to concentrate on. I do feel that all the 'socializing' on or near the active sectors is becoming more and more of a distraction.

Original NASA ASRS Text

Title: ZDC MISSES MD80 READBACK AND ACFT DSNDS INTO CONFLICT WITH LEVEL, ENRTE B738.

Narrative: I WAS WORKING 2 ACFT -- 1 LNDG IAD, 1 LNDG BWI. THE IAD ACFT WAS AT FL250 AND FASTER AND IN FRONT OF THE BWI ACFT. TURB WAS BEING RPTED AT FL280-FL290. NORMALLY BWI ACFT ARE DSNDED TO FL290 IN MY SECTOR. I ELECTED TO DSND THE BWI TO FL270 WHERE THE AIR WAS RPTED AS SMOOTH. I LOOKED AT THE IAD ACFT AT FL250, THEN THOUGHT I ISSUED THE BWI ACFT FL270 FROM FL290. I ACTUALLY SAID FL250. I NOTICED THE BWI ACFT DSNDING THROUGH FL270 AND RESTATED THE ASSIGNED ALT OF FL270 (WHICH I THOUGHT I HAD ISSUED). THE ACFT THEN CLBED BACK UP TO FL270 AFTER DSNDING DOWN TO FL257. THE ACFT WERE NO CLOSER THAN 4 MI LATERALLY AND 700 FT VERTLY. HAVING TO CONCENTRATE ON ISSUING CLRNCS THEN HEARING THE READBACK IS STRENUOUS ENOUGH. THE NOISE IN THE AREAS FROM PEOPLE TALKING AND JOKING AROUND IS MAKING THAT EVEN HARDER TO CONCENTRATE ON. I DO FEEL THAT ALL THE 'SOCIALIZING' ON OR NEAR THE ACTIVE SECTORS IS BECOMING MORE AND MORE OF A DISTR.

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.