On March 13, 1993, at 0832 central standard time, IFR separation was lost between N426MQ, an ATR 42, operated as Simmons Flight 4321, and N1801U, a McDonnell Douglas DC-10, operated as United Airlines Flight 1206. Simmons Flight 4321 had departed on Runway 32R and United Flight 1206 had departed on Runway 32L just prior to the loss of separation. Instrument meteorological conditions prevailed and IFR flight plans were filed. There was no damage or injuries reported as a result of this incident. Just prior to the loss of separation the Tower Area Supervisor initiated the coordination to change the arrival and departure runway configurations. The change was from departures and arrivals on both 32L and 32R to departures on 32R and arrivals on 32L. Runway 32L was being controlled by the South Local Controller (SLC) and 32R was being controlled by the North Local Controller (NLC). Prior to the configuration change the NLC and the SLC had agreed that the NLC would turn his westbound departures to a heading no less than 340 degrees to provide the required 15 degree separation in case an airplane landing on runway 32L had to make a missed approach. The events of the loss of separation occurred as follows: At 0830, the NLC instructed Simmons 4321 to taxi into position and hold on runway 32R. Three seconds later the SLC cleared United 1206 into position and hold on runway 32L. (This airplane was residual traffic waiting for departure on runway 32L prior to the change in runway configuration.) At 0831 Simmons 4321 was cleared for takeoff on runway 32R and was issued a heading of 340 degrees by the NLC. One second later, United 1206 was cleared for takeoff and told to turn left heading 250 degrees by the SLC. At 0832, the NLC cleared Simmons 4321 to turn left to a heading of 270 degrees followed by instructions to contact departure control. The loss of separation occurred as Simmons 4321 was making this turn and United 1206 had not completed the turn to 250 degrees. The SLC noticed that the Simmons flight was turning to the west and instructed United 1206 to turn left to a heading of 220 degrees to establish separation minimums. Between 0831 and 0832 the NLC and the Area Supervisor had a discussion regarding departure headings to be used by the NLC. According to interviews with the NLC, he stated he questioned the Area Supervisor as to why he could not turn his westbound departures further left if there were no departures on runway 32L. He stated the supervisor said, "you can" which he took to mean that there were in fact no more departures on runway 32L. He was unaware that the SLC had just cleared United 1206 for takeoff on 32L. The NLC states that he usually coordinates these types of changes with the other local controller, but failed to do so in this case. In a written statement, the Area Supervisor denied having this conversation and stated there was a discussion regarding the use of a 340 degree heading after takeoff versus a 350 degree heading. Air Traffic Control Handbook 7110.65G, paragraph 2-14a states, "Ensure that the necessary coordination has been accomplished before you allow an aircraft under your control to enter another controller's area of jurisdiction." See Air Traffic Control/Human Performance Group Chairman's Factual Report and Attachments for CHI-93-I-A115.