Narrator: This is Science Today. In response to the September 11th hijackings, computer scientist Edward Lee of the University of California, Berkeley, has proposed an avionics system called "soft walls." This system creates invisible barriers in the sky to protect cities against attack by hijacked planes-making it impossible for a plane to go into a no-fly zone.
Lee: Many of the newer planes actually have computers that mediate the commands that the pilot issues. And it's possible to modify the software to keep the aircraft from entering spaces in which you don't want it to enter.
Narrator: The system would create a virtual bubble around a city-where the boundary of the bubble is the "soft wall" and the inside of the bubble is a no-fly zone. If a plane tries to go into a "soft wall," the computer diverts the plane and the pilot will feel an external force pushing it away.
Lee: We don't want the pilot to feel like some demon has taken over the controls. We want it to feel like there's something outside.
Narrator: Lee is currently working with Boeing on prototypes of the system. For Science Today, I'm Larissa Branin.