Reporter mistakenly descended aircraft Y instead of aircraft X, resulting in a loss of separation wi...

Attributes
ACN	462799
Time
Date	200002
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : ord.airport
Altitude	msl single value : 7000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	common carrier : air carrier
Make Model Name	ATR Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Route In Use	arrival : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : c90.tracon
Operator	common carrier : air carrier
Make Model Name	Fokker 100
Operating Under FAR Part	Part 121
Flight Phase	descent : vacating altitude
Route In Use	arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller military : 4 controller radar : 20 controller time certified in position1 : 10
ASRS Report	462799
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	atc equipment other atc equipment : edp other controllera
Consequence	faa : investigated
Miss Distance	horizontal : 1500 vertical : 800
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I had an aircraft X and an aircraft Y (similar call signs) on the frequency at the same time. I meant to descend aircraft X to 4000 ft but I descended aircraft Y to 4000 ft instead. This caused aircraft Y to get closer to aircraft Z than was planned. I turned aircraft Z away from aircraft Y to increase the separation.

Original NASA ASRS Text

Title: RPTR MISTAKENLY DSNDED ACFT Y INSTEAD OF ACFT X, RESULTING IN A LOSS OF SEPARATION WITH ACFT Z.

Narrative: I HAD AN ACFT X AND AN ACFT Y (SIMILAR CALL SIGNS) ON THE FREQ AT THE SAME TIME. I MEANT TO DSND ACFT X TO 4000 FT BUT I DSNDED ACFT Y TO 4000 FT INSTEAD. THIS CAUSED ACFT Y TO GET CLOSER TO ACFT Z THAN WAS PLANNED. I TURNED ACFT Z AWAY FROM ACFT Y TO INCREASE THE SEPARATION.

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.

Reporter mistakenly descended aircraft Y instead of aircraft X, resulting in a loss of separation with aircraft Z.