Medium Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 11
Situational Awareness; Distraction; Communication Breakdown; Training / Qualification
ATC Issue All Types; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance
Human Factors; Procedure
During training the lead aircraft was assigned to 15;000 Feet and was in hand off status to ZAU. The SID restricts the aircraft to 250 Kts; a restriction lifted by the Center. The trailing aircraft was filed for 12;000 Feet and was tower enroute to MKE. No speed restriction is assigned to tower enroute aircraft. The trainee put a 3 mile J-ring on the lead aircraft and the trailing aircraft was 4 miles behind. He then assigned normal speed to the trailing aircraft. I immediately queried him on this; citing that this was not positive control and was creating a situation that we had to watch. The trainee did not take action. I waited for him to make a decision (my error).  Once we did the aircraft was 2.7 miles and 900 feet.Take action sooner.
C90 instructor observes a speed related issue with two aircraft; the second on faster than the first. He advises the Developmental; but waits too long for the Developmental to do anything and has a loss of separation.