Airplane Finding Runways in Fog

Q: So how does a plane find the runway during lousy weather? Those foggy landings always scare me.

The standard procedure for bad-weather approaches is, and has been for decades, something called the Instrument Landing System, or ILS. Essentially, a plane follows two guidance beams, one horizontally and one vertically. Transmitted from antennae on the ground, these guide an airplane along a descending path to the runway with unfailing accuracy. By centering the two beams in a kind of electronic crosshair, either manually (flying an approach by hand), or automatically (the autopilot flies and the pilots monitor), an airplane descends to a certain height — usually about 200 feet above the ground — at which the runway must be visible for landing.

Some ILS are certified for lower visibility approaches than others, and in certain cases zero-visibility landings are authorized. For these, the airplane and the crew must meet various qualifications. GPS, while in general use for enroute navigation, is still an incipient technology when it comes to bad-weather landings.

This Q&A is part of a collection that originally appeared on Patrick Smith, 38, is an erstwhile airline pilot, retired punk rocker and air travel columnist. His book, Ask the Pilot (Riverhead) was voted “Best Travel Book of 2004” by Patrick has traveled to more than 55 countries and always asks for a window seat. He lives near Boston.