I hope the answer is better than “winging it.”
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There’s a system called “ILS”, Instrument Landing System. That basically consists of a few transponders on the ground near the airport. The plane receives the signals and can calculate it’s current position, speed, descent rate and angle of descent from these signals. Pilots see this on their screens and can land perfectly.
There are a lot of radio navigation systems on board airplanes. Of course they use GPS which is integrated into their navigation instruments but the airport is also sending out different radio signals in different directions that the airplanes can tune into in order to know where they are in relation to the airport and runway. These are called VOR, ILS and GSI and get the airplanes very close to the runway. Once they are lined up for the approach and getting close they might be able to see some of the strong lights at the runway. One of the systems is called PAPI and consists of four spotlights aimed at the incoming airplanes, depending on the angle they show different colors indicating to the pilots if they are comming inn too high or too low. To find out when they hit the runway the airplanes have a radar to measure the distance to the ground with a voice reading out the distance as they approach the ground.
They use fancy machines to determine position and hight. This let’s them know when to do each step and when to expect the ground and how to steer.
Or they abort the attempt and go to another airport
If the fog is bad enough, they don’t. They will try to divert to other airports. I believe that in general, for daylight landing, you need a 1,000ft “ceiling” and one-mile visibility, and for night-time, 1,000ft ceiling and two-mile visibility.
Pilots have “instrument rating” which means they have to be able to fly on instruments. That lets them fly the plane in low or zero visibility, and various radio beacons and GPS systems can guide them to the airport itself. Once they’re within visible range, the runway lights and guidance from air-traffic control guide them in. In an emergency, with all these tools they can accomplish a landing with extremely low visibility.
Each airport has a transponder that allows planes to determine their position relative to the runway, regardless of whether or not it’s visible to the pilots. This is known as the Instrument Landing System or ILS. When pilots train for instrument flight, they actually wear a big visor that keeps them from seeing out the windshield, they have to fly and land using only the instruments.
They’re flying on instrument rules anyway rather than visual rules. Instrument flight rules are generally used by commercial aircraft so they aren’t restricted to what they can see (and because instruments are more precise than just going by visual).
This doesn’t directly apply but there is a line from “The Hunt For Red October” where the navigator says something like “give me a map and a stopwatch and I can fly the alps blindfolded.” Before GPS and radio beacons and such pilots used to (and probably still can) fly in zero visibility as long as they have a map, a compass, an altimeter, and they know where they started. Time/speed/distance calculations can be a pain but they do work.
I seem to remember in the early days of flight when everyone was trying new shit, somebody made a plane with no windows and flew from one airport to another, include taking off and landing, using a stopwatch and charts
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