Flying In Fog: What Procedures Are In Place To Keep Planes & Their Occupants Safe?

Travelers and flight crew members all want a safe and smooth flight that departs and arrives on schedule. However, certain weather conditions, like thick fog, cause low visibility conditions that present significant challenges. These issues are especially impactful on taxiing, takeoff, and landing operations. Let’s explore the tools and procedures used in the aviation industry to ensure safe flying in foggy weather.

How does fog wreak havoc on the ground?

According to the World Meteorological Organization, fog is the suspension of microscopic droplets of water. It may cover a large area or form disjointed patches on the airfield. In the aviation industry, if such conditions result in horizontal visibility of less than about 3,281 feet (1,000 meters), then fog is contributing to low visibility.


Taxiing in dense fog is challenging because it can be difficult to accurately assess the aircraft’s position on the airfield. Pilots may not be able to see all the runway lighting and the tower controller experiences the same low visibility challenges as the pilots. In this scenario, taxiing speed is reduced to ensure that the aircraft is staying on the right path. Additionally, when pilots are uncertain of their position at the airport, they may need to stop the aircraft and check in with ground control.

Fog challenges in takeoff and landing

Interestingly, fog does not present as much difficulty when an airplane is flying at altitude. Air traffic control is able to monitor radar signals that detect moving aircraft and provide direction.

Airports provide data points on the minimum visibility required to depart, called the takeoff minima. Airlines may also have their own minima, which may be influenced by the type of aircraft flown and available equipment.

Takeoff minima are determined by the measurements at the touchdown, mid-point, and stop-end points on the runway, where sensors measure visibility. This set of three data points is referred to as the Runway Visual Range, or “RVR.” If all three figures meet the takeoff minima, the aircraft may take off.

Like takeoff minima, there are also minimum standards for approach. One category of precision approach uses the Instrument Landing System (ILS), in which the aircraft detects signals projected from the runway and displays them on the flight deck screen. These signals are highly accurate and, therefore, reliably used in thick fog.

Precision approach operations are defined according to the applicable Decision Height, measured at ground level, Decision Altitude, measured above mean sea level, and RVR data. In a Category I approach, the normal ILS approach, either a Decision Altitude or Decision Height may be used. The vertical minima are measured by reference to a barometric altimeter.

Pilots have instruments that assist with landing in low visibility. Photo: Airbus

For Category II and III approaches, a greater level of precision is required. Decision Height with reference to a radio altimeter, which measures the height of an aircraft above terrain immediately below, is used to measure the vertical minima.

Flight crew personnel keep an eye on the weather conditions at the destination, so if the available information indicates that there will be foggy conditions awaiting the flight, ideally, there is enough time to plan. As a last resort, flights may be diverted to another airport for landing if there are adverse weather circumstances at the destination airport.

Source: World Meteorological Organization

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