Wrong aircraft responded to descent clearance and conflicted with another aircraft.

Attributes
ACN	120591
Time
Date	198908
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : rfd
State Reference	IL
Altitude	msl bound lower : 27500 msl bound upper : 29000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau tower : san
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : flight engineer pilot : instrument pilot : private
Experience	flight time last 90 days : 180 flight time total : 13000 flight time type : 4000
ASRS Report	120591
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 200 flight time total : 13000 flight time type : 6500
ASRS Report	120599
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Miss Distance	horizontal : 24000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error Pilot Deviation

Narrative:

I understood and read back a descent clearance from FL290 to maintain FL240 25 mi west of the rockford VOR. At about FL275 the controller gave us a heading of 180 degrees for traffic avoidance and questioned the altitude we were cleared to. Subsequent conversation with ZAU revealed that an operational error had been made and that the clearance that I read back was meant for another aircraft. I believe the cause of the incident was caused by a combination of overused airspace, excessive radio xmissions and closely spaced aircraft. This type of incident can be minimized by extraordinary attention to radio conversation. Technology that enables altitude clrncs to be issued and acknowledged west/O multiple radio xmissions that can interfere with or block each other is needed to eliminate this serious problem that results in this type of altitude deviation.

Original NASA ASRS Text

Title: WRONG ACFT RESPONDED TO DESCENT CLRNC AND CONFLICTED WITH ANOTHER ACFT.

Narrative: I UNDERSTOOD AND READ BACK A DSCNT CLRNC FROM FL290 TO MAINTAIN FL240 25 MI W OF THE ROCKFORD VOR. AT ABOUT FL275 THE CTLR GAVE US A HDG OF 180 DEGS FOR TFC AVOIDANCE AND QUESTIONED THE ALT WE WERE CLRED TO. SUBSEQUENT CONVERSATION WITH ZAU REVEALED THAT AN OPERROR HAD BEEN MADE AND THAT THE CLRNC THAT I READ BACK WAS MEANT FOR ANOTHER ACFT. I BELIEVE THE CAUSE OF THE INCIDENT WAS CAUSED BY A COMBINATION OF OVERUSED AIRSPACE, EXCESSIVE RADIO XMISSIONS AND CLOSELY SPACED ACFT. THIS TYPE OF INCIDENT CAN BE MINIMIZED BY EXTRAORDINARY ATTN TO RADIO CONVERSATION. TECHNOLOGY THAT ENABLES ALT CLRNCS TO BE ISSUED AND ACKNOWLEDGED W/O MULTIPLE RADIO XMISSIONS THAT CAN INTERFERE WITH OR BLOCK EACH OTHER IS NEEDED TO ELIMINATE THIS SERIOUS PROB THAT RESULTS IN THIS TYPE OF ALT DEV.

Data retrieved from NASA's ASRS site as of August 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.