Dense fog, which can severely limit visibility, requires pilots and air traffic controllers to use special procedures for takeoffs and landings.
Airport Fog Disruptions
Airport fog can disrupt airline operations. Depending on the season, fog causes thousands of flight delays/cancellations worldwide each year. Delays/cancellations are more common during winter when cold temperatures combine with high humidity to create greater fog risks.
Dense fog at Heathrow Airport. (Photo: PA)
Low Visibility Procedures (LVP)
Under normal conditions, air traffic controllers (ATCs) and pilots rely on visual cues and data for aircraft movement. When fog reduces visibility at an airport to less than 600 meters, the airport switches to Low Visibility Procedures (LVP). LVP involves operational adjustments to ensure more time and space on the airport for safe operations.
Taxiing
The most challenging part of flying in fog is not takeoff or landing, but taxiing. Due to reduced visibility on the tarmac, pilots and ATCs rely on charts and limited communication. When starting to taxi, the aircraft must reach a farther-than-normal roll-out point to maximize the distance before takeoff.
According to The Points Guy, a pilot, noted that taxiing becomes even more challenging because entering a runway with limited visibility can be catastrophic. That's why pilots opt to stop taxiing altogether and communicate with ATCs even when they might be a little off-course.
Takeoff
Once an aircraft successfully taxies to the runway, the crew must reassess visibility conditions. Different aircraft and airports have minimum visibility requirements for takeoff, which vary depending on the location on the runway. Only when the aircraft meets the minimum visibility requirement at all points on the runway does the ATC clear the aircraft for takeoff.
Additionally, the runway must remain clear until the aircraft is airborne, meaning no other aircraft can occupy the roll-out point until the preceding aircraft is safely aloft. This is one reason for flight delays. As the aircraft begins its takeoff roll, the pilot must make sure the plane is perfectly centered on the runway and be vigilant for any abnormalities.
Landing
Landing in LVP is also a complex task. Due to the minimum visibility requirement of 550 meters for a manual landing, pilots rely on the autopilot to execute the landing. To land in low visibility, airports require an Instrument Landing System (ILS) to guide the aircraft through the fog.
After being cleared to land by ATC, the pilot engages the autoland function to descend onto the runway and complete the landing while monitoring the system to ensure everything is proceeding smoothly. They only regain control of the aircraft once it has landed and commenced taxiing towards the terminal. As with takeoff, the runway must remain clear until the aircraft exits the runway.
Summary
The foggiest airport in the world is in California. Arcata-Eureka Airport experiences so many foggy days that the U.S. Navy uses it to test fog-reduction systems and train for all-weather operations.