When clouds surround an airport, pilots have been able to find the path to the runway for decades by using an Instrument Landing System, or ILS. Ground-based transmitters project one radio beam straight down the middle of the runway, and another angled up from the runway threshold at a gentle three degrees.

Pilots rely on a sophisticated combination of ground-based navigation aids, onboard technology, and Air Traffic Control (ATC) guidance to find the runway when visibility is obscured by clouds. The primary tool used is the Instrument Landing System (ILS), which transmits radio beams from the runway to the aircraft. These beams provide both lateral guidance (the localizer) to keep the plane centered on the runway and vertical guidance (the glide slope) to ensure the correct descent angle. Modern aircraft are also equipped with GPS and Performance Based Navigation (PBN), allowing for high-precision RNAV (Area Navigation) approaches. Additionally, pilots use an Electronic Flight Instrument System (EFIS) to monitor their position on a moving map display. In extremely low visibility, some aircraft use Autoland systems or Heads-Up Displays (HUD) with Enhanced Vision Systems (EVS) that use infrared cameras to "see" through the fog. Throughout the process, ATC provides "vectors," which are specific headings that guide the pilot toward the final approach path until the cockpit instruments "capture" the electronic signals from the runway.