Air traffic control questions

From: (Katie Schwarz)
Organization: University of California, Berkeley
Date:         08 Jun 94 12:45:35 
Followups:    1 2
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I like to listen to the air traffic control talk that United sometimes
puts on one of the audio entertainment channels, and I have some naive
questions about it. My impression is that after the pilot calls the
ARTCC (Oakland Center, Denver Center, Indianapolis Center, etc) the
person on the ground finds the aircraft on radar and follows it. Is
this right? If so, what area is completely covered by radar (contiguous
United States? North America?) How far can the radar follow a plane flying
across an ocean?

How does the ground control know which aircraft they're seeing -- by the
transponder? I don't remember ever hearing the controllers ask "what are
you squawking?" although I think the plane is told what to squawk before
taking off; why don't they need to ask?

Also, what's happening with the new air traffic control software that IBM
is supposed to be developing? Why is it behind schedule and over budget?

thanks for your answers,
Katie Schwarz