Background
Northwest Airlines Flight 354, a Boeing 727, was en route east-northeast on airway J-158. A United States Air Force EC-135, designated Slum 51, was operating on a radial-distance (R/D) flight plan, flying between R/D points south of J-158.
Incident
As Slum 51 approached its most western point, its crew requested a right turn to an R/D point that was not the next listed point on their flight plan. The trainee controller (T/C) did not realize that Slum 51 was requesting a route change. Instead, the T/C thought the flight wanted to turn back east to the next filed R/D point with a right turn (instead of a left turn as previously done). The T/C replied, "Unable right turn, make a left turn."
The instructor controller heard the request but thought the T/C's reply was a disapproval of a route change. As the controllers turned their attention to other heavy/complex traffic, Slum 51 continued a 270-degree left turn (to the north) and converged with Flight 354.
System Status
The primary computer (9020) was inoperative. The backup computer (DARC) had no capability of displaying projected routes or providing conflict alert. No flow control restrictions were in effect to reduce the amount of traffic.
Aftermath
Both aircraft were involved in a near collision at Flight Level 330. No further details were provided.