Air carrier DC9 started to descend to the same altitude of air carrier B737. Standard separation was lost. The clearance to descend was meant for another company aircraft. Reporter never caught the mistake.

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Attributes
ACN	445262
Time
Date	199906
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : ihd.vortac
State Reference	PA
Altitude	msl bound lower : 32400 msl bound upper : 33000
Environment
Flight Conditions	Mixed
Weather Elements	Turbulence
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zob.artcc
Operator	common carrier : air carrier
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : vacating altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zob.artcc
Operator	common carrier : air carrier
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 7 controller time certified in position1 : 6 flight time total : 80
ASRS Report	445262
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : required legal separation
Independent Detector	atc equipment : conflict alert other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : returned to assigned altitude none taken : insufficient time
Consequence	faa : investigated
Miss Distance	horizontal : 21600 vertical : 1500
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Working irl sector, radar controller, additional aircraft in sector due to choppy conditions in sector above. 2 air carrier's (aircraft X and aircraft Z) southeast to northwest, numerous wbound traffic. Both air carrier aircraft at FL330. Wbound B737 (aircraft Y) at FL310. Both air carrier aircraft need to be FL310 or lower to enter next sector. Did traffic search, saw the second jet (aircraft X) and aircraft Y B737 were in conflict and saw aircraft Z jet was clean. Thought I issued aircraft Z jet to descend to FL310. I noticed second aircraft X jet 500 ft lower than assigned altitude. I questioned the pilot said we're out of FL324 for FL310. I told him to maintain FL330. He said 'we're climbing back up.' I then told the aircraft Z jet to descend to FL310. 'Listen' clearly to what you're saying. Look at the data block to make sure that it is who you want to take action with. Think before you speak.

Original NASA ASRS Text

Title: ACR DC9 STARTED TO DSND TO THE SAME ALT OF ACR B737. STANDARD SEPARATION WAS LOST. THE CLRNC TO DSND WAS MEANT FOR ANOTHER COMPANY ACFT. RPTR NEVER CAUGHT THE MISTAKE.

Narrative: WORKING IRL SECTOR, RADAR CTLR, ADDITIONAL ACFT IN SECTOR DUE TO CHOPPY CONDITIONS IN SECTOR ABOVE. 2 ACR'S (ACFT X AND ACFT Z) SE TO NW, NUMEROUS WBOUND TFC. BOTH ACR ACFT AT FL330. WBOUND B737 (ACFT Y) AT FL310. BOTH ACR ACFT NEED TO BE FL310 OR LOWER TO ENTER NEXT SECTOR. DID TFC SEARCH, SAW THE SECOND JET (ACFT X) AND ACFT Y B737 WERE IN CONFLICT AND SAW ACFT Z JET WAS CLEAN. THOUGHT I ISSUED ACFT Z JET TO DSND TO FL310. I NOTICED SECOND ACFT X JET 500 FT LOWER THAN ASSIGNED ALT. I QUESTIONED THE PLT SAID WE'RE OUT OF FL324 FOR FL310. I TOLD HIM TO MAINTAIN FL330. HE SAID 'WE'RE CLBING BACK UP.' I THEN TOLD THE ACFT Z JET TO DSND TO FL310. 'LISTEN' CLRLY TO WHAT YOU'RE SAYING. LOOK AT THE DATA BLOCK TO MAKE SURE THAT IT IS WHO YOU WANT TO TAKE ACTION WITH. THINK BEFORE YOU SPEAK.

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.