[betterunix2]

Like I said, what if one of those planes had a malfunctioning transponder? It is a somewhat stretched scenario, but the NK military might have gotten bold and decided to shoot a missile all the way to the boundary of US territorial waters or airspace. In the middle of nervously tracking a missile that seems to be headed directly toward the west coast, NORAD suddenly sees another object that looks just like an airplane heading toward LA or SF, but it is not identifying itself. Now NORAD personnel have to take time to figure out if this airplane is just a malfunctioning civilian plane or some kind of NK attack.

Sure, NORAD probably tracked the plane from whatever airport it departed from, but during the missile test they probably want to have their personnel focus every second of their attention on the missile and not on checking some flight path.