Pilots land in zero-visibility conditions (such as heavy fog or "whiteout" snow) using a sophisticated technology called the Instrument Landing System (ILS). For the most extreme conditions, they perform a Category III (CAT III) Autoland. The ILS works by projecting two highly precise radio beams from the runway: the "Localizer," which provides horizontal guidance to keep the plane centered on the runway, and the "Glide Slope," which provides vertical guidance for the correct angle of descent. On the flight deck, these beams are translated into digital "crosshairs" on the primary flight display. In a CAT III landing, the aircraft's autopilot and autothrottle systems take full control of the flight path, using redundant computers to fly the plane all the way to touchdown. The pilots act as "system monitors," ready to take over only if a system failure occurs. Once on the ground, they may also use a "Head-Up Display" (HUD) or "Enhanced Vision Systems" (EVS) that use infrared cameras to highlight the runway lights through the fog. This technology ensures that even if a pilot cannot see past the nose of the plane, they can land with surgical precision.