What happened
During a standard instrument departure, Alaska Airlines Flight 601, operating N954AS, experienced a near collision with a Mooney M20C, registration N91Y. At the time of the event, the Mooney was transiting the Reno airspace at 12,500 feet MSL.
The incident involved several lapses in air traffic control procedures. The local controller failed to instruct Alaska Airlines Flight 601 to contact departure control following its takeoff. Simultaneously, the departure controller/area manager left his workstation to attend to a telephone call from a facility technician regarding TRACON business.
During this period, the arrival controller was managing the Mooney aircraft, instructing the pilot to change transponder codes in preparation for a handoff to Center. This instruction led to confusion between the Mooney pilot and the controller regarding the specific code. Consequently, the arrival controller's attention was diverted away from the data block for Alaska Airlines Flight 601.
Findings
The investigation revealed that the changing of transponder codes and the intermittent Mode C functionality of the Mooney aircraft prevented the Traffic Collision Avoidance System (TCAS) on Alaska Airlines Flight 601 from acquiring the Mooney. Following the telephone call, the departure controller attempted to contact Alaska Airlines Flight 601 via radio but was unable to establish communication. The controller then contacted the local controller, who subsequently reported that a near collision had occurred.