What happened
During a transition in runway configuration, the airport was moving from using both runways 32L and 32R for arrivals and departures to a new setup where departures would use 32R and arrivals would use 32L. During this period, the North Local Controller (NLC) cleared Simmons 4321, an ATR-42, for takeoff from runway 32R. Following the takeoff clearance, the crew was instructed to execute a left turn to a heading of 270 degrees.
Shortly thereafter, the South Local Controller (SLC) cleared United 1206, a DC-10, for takeoff from runway 32L. As United 1206 became airborne, the ATR-42 had already commenced its left turn. This maneuver placed the aircraft directly in the departure path of the DC-10, resulting in a loss of separation where vertical separation was reduced to zero feet and lateral separation was reduced to 0.5 miles.
The investigation
The investigation examined communications between the North Local Controller and the area supervisor. The NLC stated that during a previous discussion regarding departure headings (specifically for scenarios where there were no departures on runway 32L), he believed the area controller had indicated that a left turn would be permissible. However, the area supervisor denied that such a discussion regarding left turns had taken place. The supervisor maintained that his recollection of the conversation pertained only to choosing between a 340-degree heading and a 350-degree heading to provide protection for missed approaches.