Air Traffic Control Developmental
Communication Breakdown
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action
Human Factors; Procedure
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.
We checked in with ORD departure with our heading (180) and altitude (5;000 FT). The Controller acknowledged and no further instructions were given. I saw the conflict aircraft on TCAS and noticed it was descending below 6;000 FT and getting closer. When the aircraft was about 3 miles horizontal and 500 FT vertical from us on the TCAS I queried ATC with no response. I queried again and right then we received a 'Descend' RA. I pushed the nose down and started to make a left turn to pass behind the conflict aircraft (moving from left to right). We announced to ATC that we were in a 'TCAS descent.' After receiving the 'clear of conflict' message we returned to our original assigned heading and 5;000 FT altitude and advised. At this time we did acquire the conflict aircraft visually. The Controller asked if we had received an RA and we replied 'yes.'
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.