Can Planes Land in Fog

Driver Abilities

Intuitively, pilots need to be trained to a higher level to allow the autopilot to do the landing rather than doing it themselves. They must undergo specific training to ensure that they are qualified in “Low Visibility Procedure” (LVP). If the pilots have not undergone this specific training and have been validated as competent, they are only authorized to manually land the aircraft. This training must be completed once a year and consists of take-off and landing in thick fog as well as dealing with technical malfunctions that require the approach to be aborted at low altitude.

Airport capacities

The airport itself must have certain infrastructure in place to allow Autoland aircraft. This comes in the form of navigation equipment such as an Instrument Landing System (ILS). There are different categories of ILS which allow landing in certain visibilities. Most of the time, a CAT 1 ILS is used which directs the pilots 200 feet above the airport, at which point they disconnect the autopilot and land manually. However, in low visibility conditions where the visibility is less than 550m, a higher category of ILS must be fitted to enable an Autoland to be performed, for example a CAT 2 or CAT 3 A/B or C.

The category of the ILS is determined by the precision with which it guides the aircraft. The type of approach and runway lights available that help pilots locate and orient themselves with the runway and the number and type of backup ILS systems (e.g. backup generator to power the ILS) also determine the ILS category.

ILS protection area

When visibility drops below approximately 600 meters, an airport will introduce ‘low visibility procedures’. This triggers the introduction of certain protocols that must be followed by air traffic control, all aircraft and certain vehicles operating at the airport.

These procedures introduce a protected area around the Instrument Landing System (ILS), which is a radio navigation aid used to guide the aircraft to landing. The protected area stops vehicles and aircraft maneuvering on the ground, approaching too close to the Locate and Glide Path (ILS) antenna when other aircraft are about to land. If there is movement near the ILS antenna, it could potentially disrupt the guidance signal sent to the aircraft. When there is fog, as pilots cannot see the ground until the final seconds of landing, the accuracy of these radio aids is essential to ensure the aircraft continues on its course to the runway. . Signal disruption when the aircraft is at low altitude, and when the pilots cannot see the runway, can be dangerous.

Why are flights delayed and canceled when there is fog?

When planes take off, land and taxi near the runway, they enter the protected area. In order to ensure that aircraft on final approach are not affected by signal disturbance, a greater distance between aircraft taking off and landing is required. This means that when an aircraft taxis into the ILS protected area, the next aircraft on final approach is still a number of miles away and still quite high, so any potential signal interference is not dangerous. At busy airports, aircraft landings are normally much closer than this. The requirement to increase spacing between aircraft when there is fog that the airport can allow means that fewer aircraft take off every hour. This significant reduction in the airport’s take-off and landing capacity is the reason why there may be flight delays and cancellations on foggy days.

When visibility is reduced, more caution should be exercised when taxiing the aircraft around the airport. It is much harder to see where you are going and other aircraft and vehicles maneuvering on the ground can be difficult to spot. Anything that moves, does so at a much slower speed. As a result, far fewer planes are allowed to taxi around the airport at any given time. In a busy airport, this inevitably means that flights will be delayed or cancelled.

An example of flight delays due to fog

When an aerodrome is operating near full capacity (such as London Heatrow or JFK in New York), there will inevitably be flight delays and cancellations in foggy conditions. This is because there must be greater separation between landing planes and few planes are allowed to taxi at any given time.

The ILS sends a radio beam to the approaching aircraft which directs it to the runway. As pilots may not see the runway until the final seconds of the approach, they are entirely dependent on an accurate ILS radio beam directing the aircraft onto the runway. Therefore, the ILS radio beam (which must be located very close to the runway) must be protected to prevent any interference that could cause an aircraft to deviate from its path.

If aircraft landing and taking off get too close to the ILS equipment emitting the radio beam, it can cause interference. Therefore, landing aircraft must move a little further from the runway after landing than normal to ensure that the next approaching aircraft is not affected by any interference.