What happened
The incident involved Ozark Flight 709, operated by a DC-9 with registration N923L, which had been cleared by the Kansas City Air Route Traffic Control Center (ZKC) to cruise at flight level 270. While traversing east-southeast near the boundary of the ZKC sector, the airliner began to converge on a formation designated as Zorro 11, consisting of three F-4 fighter aircraft.
The military fighters had previously been cleared by the Indianapolis ARTCC (ZID) to proceed westbound at flight level 260. Their objective was to rendezvous with a KC-135 tanker, identified as Shake 81, for aerial refueling along route AR110W. This route originated within the ZID airspace and extended westward into the ZKC area. The tanker was orbiting under the control of ZKC and had been authorized to maintain an altitude block between flight level 260 and 290.
A critical procedural error occurred when ZID cleared the F-4s to switch to the tanker's radio frequency. This clearance was issued without handing the fighters over to ZKC or obtaining approval from either the Kansas City center or the tanker crew. Upon establishing radio contact, the tanker crew incorrectly instructed the F-4s to climb to flight level 270.
When the ZKC controller recognized that the military formation and the DC-9 were on converging paths, he immediately directed the Ozark crew to turn left. The pilots of Flight 709 visually acquired the fighters and executed evasive action to avoid a collision. It was determined that ZID had failed to properly coordinate the position of the F-4s, and none of the pilots involved were informed of the conflicting traffic.