C90 controller and emb-145 first officer described a conflict event when an arrival aircraft descend...

Narrative:

I was working south departure while ord arrivals were going to runway 4R and 10. I radar identified an E145 departure off ord heading 140 climbing to 5;000 ft. I turned the aircraft south to tunnel under the arrivals that were at 70. A supervisor was standing behind to tell me about a go-around I would be getting off of runway 4R; when I heard an aircraft say their callsign 'the E145'. That wasn't his callsign; but I noticed right away that the E145 had traffic right in front of it descending to their altitude. The traffic was an A320. It was an arrival for runway 4R on a westbound heading; descending to I don't know what. The A320 should have not been lower than 7;000 ft. By the time I noticed the A320; he was already at 5;200 ft. I immediately called traffic to the E145 and told him to turn. I believe both aircraft were already in the process of responding to a RA. Once the altitudes were corrected and traffic was no longer a factor; the E145 continued without further incident. I didn't know this until today; but I was told this is a continuous problem for aircraft being vectored for runway 4R. Some aircraft respond to the runway assignment as a clearance to descend to 4;000 ft. I'm not one for extra phraseology; but maybe restate the altitude assignment when assigning runway 4R.

Original NASA ASRS Text

Title: C90 Controller and EMB-145 F/O described a conflict event when an arrival aircraft descended below issued altitude toward a departure aircraft being tunneled underneath; the C90 Controller reporter noting a Runway 4 assignment may have been confused with a 4;000 altitude clearance.

Narrative: I was working south departure while ORD arrivals were going to Runway 4R and 10. I RADAR identified an E145 departure off ORD heading 140 climbing to 5;000 FT. I turned the aircraft south to tunnel under the arrivals that were at 70. A supervisor was standing behind to tell me about a go-around I would be getting off of Runway 4R; when I heard an aircraft say their callsign 'The E145'. That wasn't his callsign; but I noticed right away that the E145 had traffic right in front of it descending to their altitude. The traffic was an A320. It was an arrival for Runway 4R on a westbound heading; descending to I don't know what. The A320 should have not been lower than 7;000 FT. By the time I noticed the A320; he was already at 5;200 FT. I immediately called traffic to the E145 and told him to turn. I believe both aircraft were already in the process of responding to a RA. Once the altitudes were corrected and traffic was no longer a factor; the E145 continued without further incident. I didn't know this until today; but I was told this is a continuous problem for aircraft being vectored for Runway 4R. Some aircraft respond to the runway assignment as a clearance to descend to 4;000 FT. I'm not one for extra phraseology; but maybe restate the altitude assignment when assigning Runway 4R.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1006890
Time
Date	201204
Local Time Of Day	1201-1800
Place
Locale Reference	ORD.Airport
State Reference	IL
Aircraft 1
Make Model Name	EMB ERJ 145 ER/LR
Operating Under FAR Part	Part 121
Flight Phase	Initial Climb
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Departure Approach
Qualification	Air Traffic Control Developmental
Person 2
Function	First Officer
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Procedural Published Material / Policy

C90 controller and emb-145 first officer described a conflict event when an arrival aircraft descended below issued altitude toward a departure aircraft being tunneled underneath; the C90 controller reporter noting a runway 4 assignment may have been confused with a 4;000 altitude clearance.