Air Traffic Control Fully Certified
Other / Unknown
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Procedure
MDW was using a combination of RNP/RNAV Y 13C and Visual Approach 13C all afternoon. Typically; when 13C is in use; ORD protects for the MDW 13C ILS. However; since the ILS was not in use today; ORD was operating as normal with their southbound departures off Runway 22L. When traffic to MDW was light; it wasn't really a big deal. However; with the evening rush; it became more of a problem. Due to MDW's size and also the vast sea of orange lights that is the Metro Chicago area; visuals became a bit more difficult to achieve after sunset. Right now; only one airline is certified to use the RNP Y 13C Approach; and even then; not all of their aircraft are capable. The evening rush included several GA aircraft along with other air carriers which really forced our hand to use visuals. Earlier in the shift; I had asked a CIC to call MDW and see if we could use Runway 31C since the winds were fairly light. I saw one air carrier proceeding on a wide base leg; outside of the RNP Y final approach course. I told him to turn right to heading 090 to continue following the traffic; to which he replied; 'roger; we still have our traffic in sight.' I then switched the aircraft to Tower frequency about 7 miles from the airport. Just then; I saw an air carrier departing ORD Runway 22L southbound; climbing slowly; but assigned the ORD6 SID. The line's FLM-IC saw what was going on and took action to change the advertised approach in use at MDW to the GPS 4R circle to 13C to avoid further issues. I was later told that separation was lost. Under light traffic; using this combination of visuals and RNP Y 13C approaches works; however; under any real load; it quickly becomes a difficult operation which has no built-in safeguards to protect MDW inbound traffic from ORD departure traffic. If Runway 13C is required; then ORD needs to protect for it.
C90 Controller described a loss of separation event involving arrival traffic into MDW and departure traffic from ORD; the reporter suggesting amending procedures when this combination of runways are required.