TRACON II is the follow on a software program simulating an air traffic control environment on a personal computer. The game shipped with three sectors: San Francisco, Boston, and Los Angeles. These are simplified but spatially-accurate models of regions. Wesson sold additional packs of sectors simulating other parts of the US.
In the game, aircraft with a flight plan involving a landing must be vectored to a proper altitude at the start of the approach pattern. For example, if the approach started at 1,700 feet on a heading of 170 degrees, the player needed to get the aircraft near that altitude and heading. At that point, the aircraft is handed off to the approach controller. The aircraft responds, "aa34 switching to tower frequency." This changes the aircraft's icon to flash in a different color. If successful, the icon would change to, "AA34 is landing."
Source: Wikipedia, "Tracon II", available under the CC-BY-SA License.