It's not so much the direction as it is the location of the aircraft along the runway. Boeing Field (KBFI) has a number of recognizable landmarks along the run

It's not so much the direction as it is the location of the aircraft along the runway. Boeing Field (KBFI) has a number of recognizable landmarks along the runway (as seen in the discussion), so some of the theories advanced had to do with whether or not the aircraft could be in a given phase at the recorded location.