ZTL controller descended an atl arrival through occupied altitude.

Attributes
ACN	707966
Time
Date	200608
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ztl.artcc
State Reference	GA
Altitude	msl bound lower : 27000 msl bound upper : 28000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl.artcc
Operator	general aviation : corporate
Make Model Name	Bonanza 35
Operating Under FAR Part	Part 91
Flight Phase	climbout : initial
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : ztl.artcc
Operator	common carrier : air carrier
Make Model Name	Regional Jet CL65 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller military : 4 controller radar : 21
ASRS Report	707966
Person 2
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	atc equipment : conflict alert other controllera
Resolutory Action	controller : issued new clearance controller : issued alert
Consequence	faa : investigated
Miss Distance	horizontal : 12000 vertical : 900
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance

Narrative:

Aircraft #1; GA; checked on rocket sector; of ZTL frequency; climbing to or level at FL230; requesting FL270. Aircraft #1 was sebound. Aircraft #2 was a commercial airline inbound to atl. Atl was on an east operation requiring arrs to be both lower and slower farther from the airport. I descended the air carrier to FL280 as aircraft #1 was requesting FL270. FL270 was in aircraft #1's data block as a hard altitude. When the loss of separation occurred; I was sure I had cleared aircraft #1 to climb and maintain FL270. The tape revealed a clearance and acknowledgement of FL280. Staffing at ZTL has recently been very low. Controllers are routinely required to work over 2 hours without relief and break periods have been drastically reduced.

Original NASA ASRS Text

Title: ZTL CTLR DSNDED AN ATL ARR THROUGH OCCUPIED ALT.

Narrative: ACFT #1; GA; CHKED ON ROCKET SECTOR; OF ZTL FREQ; CLBING TO OR LEVEL AT FL230; REQUESTING FL270. ACFT #1 WAS SEBOUND. ACFT #2 WAS A COMMERCIAL AIRLINE INBOUND TO ATL. ATL WAS ON AN E OP REQUIRING ARRS TO BE BOTH LOWER AND SLOWER FARTHER FROM THE ARPT. I DSNDED THE ACR TO FL280 AS ACFT #1 WAS REQUESTING FL270. FL270 WAS IN ACFT #1'S DATA BLOCK AS A HARD ALT. WHEN THE LOSS OF SEPARATION OCCURRED; I WAS SURE I HAD CLRED ACFT #1 TO CLB AND MAINTAIN FL270. THE TAPE REVEALED A CLRNC AND ACKNOWLEDGEMENT OF FL280. STAFFING AT ZTL HAS RECENTLY BEEN VERY LOW. CTLRS ARE ROUTINELY REQUIRED TO WORK OVER 2 HRS WITHOUT RELIEF AND BREAK PERIODS HAVE BEEN DRASTICALLY REDUCED.

Data retrieved from NASA's ASRS site as of January 2009 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.