Earlier quoted context omitted.
Re clearance/cause: VASA https://www.youtube.com/watch?v=fItu5qM7QfE also couldn't make it out, but it sounds like the Coast Guard Dash 8 got a not really perfect taxi instruction (neither "hold short" nor "line up and wait") to one of the other C* intersections leading onto 34R while a Delta flight occupied C1, but entered the runway anyway. The A350 got a proper clearance it read back correctly. Also looks like all…
Whether it was perfect or not, there are only a few words/phrases that allow an aircraft to cross the hold short bars at an airport with an active control tower. "Cross", "line up and wait", and "cleared for takeoff" are pretty much it. Runway incursions are very dangerous, as this incident shows, and pilots must be very sure they have clearance before entering a runway. If anything is ambiguous in an instruction, pi…
Line up and wait sounds like something you tell preschoolers to do :-)