How do planes operate in thick fog?

Dense fog can reduce visibility, forcing pilots and air traffic controllers to use special procedures for takeoff and landing.

Fog at the airport can disrupt airline operations. Depending on the season, fog leads to thousands of flight delays/cancellations around the world every year. In winter, cold temperatures and high humidity lead to a greater risk of fog. Therefore, flight delays/cancellations tend to occur in the winter.

Thick fog at Heathrow airport. (Photo: PA).

Under normal conditions, air traffic controllers (ATC) and pilots can control aircraft movement through maps and image data. However, when fog appears at the airport and visibility drops below 600 m, the airport switches to Low Visibility Procedures (LVP). LVP significantly adjusted operations to ensure more space and time on the airfield to conduct safe operations.

The most complicated part of flying in fog is not taking off or landing but running on the runway. Due to poor visibility over the airport, pilots and ATC were forced to rely on maps and limited communications. When starting to run, the aircraft must reach a direction point hundreds of meters farther than usual to reach the maximum distance when taking off.

According to The Points Guy - a pilot, running on the runway is even more complicated because entering the runway in low visibility conditions can cause disaster. That's why pilots choose to stop running completely and contact ATC even when the possibility that they don't know the exact location is minimal.

Take off

After the aircraft successfully reaches the runway, the crew must reassess visibility conditions. Each type of aircraft and airport has a minimum visibility for takeoff, which varies depending on the location on the runway. Only when the aircraft meets the minimum visibility criteria at all points on the runway will ATC allow the vehicle to begin takeoff.

Additionally, the runway needs to be clear until the aircraft is in the air, which means other aircraft cannot enter the waypoint before the vehicle in front is safely overhead. This is one of the reasons for flight delays. Once the takeoff roll begins, the pilot needs to make sure the plane is perfectly centered on the runway and watch for anything out of the ordinary.

Landing

Landing in LVP is also a complicated task . Because the minimum visibility for manual landing is 550 m, the pilot must rely on autopilot mode to land. In order to land in low visibility areas, airports need a landing support system to connect with aircraft in thick fog.

Once ATC approves the landing, the pilot turns on the autoland function to land on the runway and completes the landing while monitoring the system to ensure everything goes smoothly. They only regained control once the plane had landed and started heading to the terminal. Just like at takeoff, the runway needs to be clear until the plane has finished its run.

The foggyest airport in the world is located in California . Arcata-Eureka Airport experiences so many foggy days that the US Navy uses it to test fog reduction systems and do all-weather training.