How do planes land in fog?

How can you land when all you see from the window is white fog? The answer is an invisible path leading to the runway.

ILS: the invisible path

Most runways at large airports have an ILS (instrument landing system). Radio signals from the runway end give the aircraft both direction and descent angle. Following them, the aircraft lines up with the runway even without visibility.

Autoland

In very low visibility, aircraft certified for it and pilots trained for it can use automatic landing: the aircraft follows the ILS and lands itself under the pilots' supervision. Pilots monitor every stage and are ready to go around if needed.

What you feel on a foggy day

• Nothing but white out the window for a long time; the air is usually calm.
• You see the runway lights at the last moment.
• The landing is usually gentle.

Why delays happen

In fog, aircraft are spaced further apart, which cuts the number that can land per hour. That's why there may be waiting, holding or short delays at departure or arrival. Fog is most common in the morning and usually lifts as the day goes on.