It is a quiet predawn morning in the Seattle, WA area and the lone FAA air traffic controller who is controlling the airspace in the sector south of the city has been on duty for seven hours. The weather is clear with a visibility of 15 miles. The only traffic is a Navy helicopter on the East side of the controller's airspace, transiting the area westbound en route to a nearby Navy facility, and a private airplane on the Southside of the controller's airspace flying northbound. Both aircraft are operating under visual flight rules, are in contact with the controller, and flying at an assigned altitude of 3,500 ft. The controller dozes off, then is awakened by the ringing telephone, learning that the two aircraft collided in flight in the controller's airspace. There are no survivors. Investigation reveals that the two collided while in level flight at the altitude assigned each by that controller.

Analyze the potential liability of the United States and the controller for the accident. (You may find it helpful to diagram the positions and approximate tracks of the two aircraft, first.)