Background
A flight of four Air National Guard A-7 aircraft, designated Sluff 11, was operating under Indianapolis Center (CTLR-A) control. The flight was cleared to climb to FL210. Later, the controller instructed Sluff 11 to change frequency to York Low sector (CTLR-B). The flight changed frequency, but neither Sluff 11 nor CTLR-B established radio contact before Sluff 11 continued into the Richmond sector (CTLR-C's area).
Sequence of Events
Another flight, Sluff 31, cancelled its IFR clearance with CTLR-C. However, CTLR-C—a developmental controller—became confused by the similar call signs (Sluff 11 and Sluff 31) and inadvertently entered a cancellation note on the computer flight strip for Sluff 11. The instructor controller did not notice this error. The strip was handed to the D-side controller, who questioned the notation but nevertheless entered a cancellation message into the computer. This action replaced the full data block for Sluff 11 with a limited data block.
Several minutes later, Sluff 11 converged with a Boeing 727 operating as TWA Flight 489, which had been cleared to climb to FL230. The two flights subsequently passed within an estimated 500 feet vertically and 200 feet laterally of each other. The leader of Sluff 11 was on a check flight and was being evaluated by a standardization/evaluation instructor pilot (Sluff 12).
Aftermath
No collision occurred, and no injuries or damage were reported. The incident highlights the critical importance of accurate flight data management and call sign recognition in air traffic control operations.