Communications records from Seattle-Tacoma tower reveal a controller repeatedly demanded identification from a Bombardier turboprop lining up on the runway, as investigators probe the unauthorised departure of a Horizon Air Q400 from the airport.

Tower communications from around 19:33, shortly after a Delta Air Lines Boeing 737 had been cleared to land on runway 16R, show that a controller transmitted an inquiry to an unknown aircraft on the parallel runway 16C.

“Aircraft on [taxiway] Charlie lining up runway 16C, say callsign,” the controller states. Taxiway C is located at the far northern end of 16C and 16R.

After receiving no response from the aircraft, the controller asks again: “The Dash 8 on runway 16C, say your callsign.”

He repeats the inquiry, with greater insistence, and then demands: “Who’s the Dash 8 holding on 16C?”

Shortly afterwards the crew of another flight, identifying itself as Alaska Airlines 322, appears to tell the tower that the Horizon aircraft is taking off.

The tower again tries to reach the turboprop, urgently asking: “Who’s the aircraft on runway 16C?”

A further message to the tower, probably from the Alaska flight, mentions the turboprop’s wheels “smoking, left and right” as it rolls along the runway, to which the controller replies: “All right, I’m not even talking to him.”

The Seattle tower communications have been archived by the LiveATC site.

Brief subsequent discussions appear to suggest the aircraft may have emerged from a cargo area situated on the north-eastern side of the airport close to taxiway C, before a message advises that the tower needs to “call and scramble, now”.

Source: Cirium Dashboard