Owais Crawford
Fog at airports can cause significant disruptions to airline operations, resulting in flight delays and cancellations. When visibility drops below a certain level, airports switch to Low Visibility Procedures (LVPs) to ensure safe operations. While fog does not lead to airport closures, it slows down the use of runways and taxiways. Airports employ various methods, such as seeding or heating, to artificially dissipate fog and improve visibility. This includes using salt particles, downwash mixing with helicopter rotors, or heating the air near landing strips. However, these techniques only offer short-term solutions under specific conditions.
| Characteristics | Values |
|---|---|
| Impact of Airport Fog | Results in thousands of flight delays and cancellations worldwide throughout the year |
| More disruptions during winter due to colder temperatures and higher humidity levels | |
| Disruptions at London Heathrow and Delhi's Indira Gandhi International Airport due to freezing and foggy weather | |
| Fog is when visibility is less than 1 kilometer (0.6 miles) | |
| Low Visibility Procedures (LVPs) | Airports switch to LVPs when visibility drops under 600 meters (2,000 feet) |
| Pilots rely on autopilot for landing when the minimum visibility needed for a manual landing is 550 meters (approx. 1,800 feet) | |
| Airports need high-level ILS (instrument landing systems) to connect to the aircraft during thick fog | |
| Pilots use autoland to align with the runway and complete the touchdown | |
| Pilots retake control once the plane lands and the taxi begins | |
| Planes go to holding points further away than usual to allow for maximum distance when taking off | |
| Runways are kept empty until the landing aircraft clears the runways and is taxiing | |
| Fog Dispersal Techniques | Seeding fog with salt particles |
| Downwash mixing using whirling helicopter rotors to pump dry air downward into the fog layer | |
| Heating the air near landing strips with burners | |
| Using a nuclear reactor to power insanely powerful infrared heaters |
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What You'll Learn
Low visibility procedures
LVPs alter operations significantly to ensure more space and time on the airfield for safe operations. The most complicated part of flying during fog is not the takeoff or landing but taxiing to the runway. Pilots and air traffic control (ATC) rely on maps and limited visual-led communications to navigate the aircraft. Planes must go to holding points further away than usual to allow for maximum distance when taking off. This can add up to hundreds of metres to the usual holding point.
Low visibility take-off (LVTO) procedures can be implemented when the RVR is lower than 400m. Pilots must be aware of the remaining runway length using any external visual cues, such as lighting, signage, or markings. The potential for runway incursions by aircraft, vehicles, or personnel increases as visibility deteriorates. This risk can be managed by providing pilots with clear and unambiguous guidance on routing, holding points, and ground traffic patterns.
To land in low-visibility conditions, airports must have high-level instrument landing systems (ILS) to connect to the aircraft during thick fog. Once cleared for landing, pilots turn on autoland to align with the runway and complete the touchdown. Pilots only retake control once the plane has landed and is taxiing to the terminal.
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Fog dispersal techniques
Seeding
This technique involves seeding the fog with salt particles. While this method has been tried, it only provides short-term relief under specific conditions.
Downwash Mixing
Downwash mixing uses whirling helicopter rotors to pump dry air downward into the fog layer. Like seeding, this technique has limited effectiveness and only offers temporary relief.
Heating
Burning equipment is used to heat the air near landing strips, which can help dissipate fog. However, this method also falls short of providing a long-term solution and is effective only under certain conditions.
Infrared Technology
Infrared heaters have been suggested as a potential solution to heat large volumes of air. The idea is based on the principle that hot air can hold more moisture. However, the challenge lies in ensuring that the heated air is replaced by clear air, as it rises.
Instrument Landing Systems (ILS)
Airports utilize advanced ILS to guide aircraft during low-visibility conditions caused by fog. Combined with LED lighting systems, these technologies enable operations during foggy weather, albeit with reduced capacity.
Low Visibility Procedures (LVPs)
During foggy conditions, airports implement LVPs to ensure safe operations. These procedures involve altering standard practices to allow for more space and time on the airfield. Taxiing to the runway becomes particularly challenging due to the lack of visual cues.
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Impact on airport operations
Airport operations are significantly impacted by fog, which can cause flight delays and cancellations worldwide. Airports switch to Low Visibility Procedures (LVPs) when visibility drops below 600 meters (2,000 feet), altering operations to ensure more space and time for safe movements. The taxiing process is the most complicated during fog, as pilots and air traffic control (ATC) rely solely on maps and limited visual communications. To ensure safety, planes go to further holding points, adding hundreds of meters to the usual distance.
The minimum visibility required for a manual landing is 550 meters (1,800 feet), necessitating autopilot and high-level instrument landing systems (ILS) during thick fog. Freezing fog poses a severe hazard, requiring pilots to closely monitor the system during touchdown, which is more exhausting than manual landing. The runway remains clear until the landing aircraft taxis off, slowing down operations.
To improve visibility, airports employ artificial fog dissipation methods, such as seeding with salt particles, downwash mixing using helicopter rotors, and heating the air near landing strips. However, these techniques only offer short-term relief under specific conditions.
The impact of fog is more pronounced during peak morning hours, with ongoing delays dependent on its severity. Foggy weather requires coordination between airports, airlines, and aviation authorities to ensure passenger safety and resume normal operations as soon as possible. Delayed or diverted flights can lead to re-booking and logistical challenges, affecting both domestic and international travel.
Additionally, smaller airports without advanced infrastructure, such as CAT III ILS or more capable aircraft, may face greater challenges in managing foggy conditions. They may not be able to afford or implement the same fog-mitigation systems as larger airports, potentially resulting in more significant disruptions to their operations.
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Takeoff and landing processes
When an airport is covered in fog, it is forced to reduce the number of flights taking off and landing. This results in aircraft backing up at the gates and other aircraft going around in holding patterns in the air, waiting for their turn to land.
During foggy conditions, airports switch to Low Visibility Procedures or LVPs. These LVPs alter operations significantly to ensure more space and time on the airfield to carry out safe operations. The most complicated part of flying during fog is not the takeoff or landing but rather taxiing to the runway. The lack of any visuals on the airport means pilots and air traffic control (ATC) are forced to rely on maps and limited visual-led communications. Planes must go to holding points further away than usual to allow for maximum distance when taking off. This means planes may go to holding point CAT 2 or 3 instead of the usual CAT 1, adding up to hundreds of metres more to the holding point.
Before taking off, the flight crew ensures that they keep an eye on the weather conditions at the destination. If there is expected to be fog, they can plan accordingly. As a last resort, flights may be diverted to another airport for landing if there is severe fog at the destination airport.
To take off, aircraft must meet the minimum visibility criteria across all points on the runway. These criteria are determined by measurements at the touchdown, mid-point, and stop-end points on the runway, where sensors measure visibility distance levels. 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. During the takeoff roll, pilots ensure the plane is perfectly centred and monitor for anything out of the ordinary.
Landing during LVPs is a complicated task. Since the minimum visibility needed for a manual landing is 550 meters (approx. 1,800 feet), pilots must rely on autopilot for the landing. To land in low visibility, airports must have high-level ILS (instrument landing systems) to connect to the aircraft. Once ATC clears the aircraft for landing, pilots turn on autoland to align with the runway and complete the touchdown while intently watching the system to ensure everything is going well.
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Runway and apron safety
Fog can cause significant disruption to airport operations, leading to flight delays and cancellations. When visibility drops below 600 meters (2,000 feet), airports switch to Low Visibility Procedures (LVPs) to ensure safe operations. These procedures significantly alter operations to create more space and time on the airfield.
During LVPs, the most complicated part of flying is not takeoff or landing but taxiing to the runway. Pilots and air traffic control (ATC) rely on maps and limited visual-led communications to navigate. Planes also go to further-away holding points to allow for maximum distance when taking off.
Shallow fog can reduce visibility and obscure objects below eye level, including signage, taxiway, and runway markings. This can be even more challenging if there is a low sun angle that results in glare. Vigilance is required from both pilots and ground crew during pushback and start procedures to avoid potential hazards caused by obscured vision.
To ensure runway and apron safety during fog, pilots should discuss anticipated taxi routes as part of the approach and landing briefing. Checklists should be completed while the aircraft is stationary, and both pilots should closely monitor the aircraft's position when in motion. If there is any doubt about the parking area being clear, the aircraft should be stopped and await further guidance or be shut down and towed onto the stand.
Additionally, runway centreline lights can provide additional guidance during takeoff, and it is recommended to avoid taking off towards the sun to minimize glare. Airports with appropriate category Instrument Landing Systems (ILS) can facilitate safe landings for most modern commercial transport aircraft equipped with auto-land capabilities. However, for non-auto-land aircraft, shallow fog can pose a significant hazard.
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Frequently asked questions
Fog and mist are just clouds sitting on the ground. It is formed when warm, moist air moves over a colder surface and condenses.
Airport fog significantly disrupts airline operations, causing thousands of flight delays and cancellations worldwide. Airports switch to Low Visibility Procedures (LVPs) when visibility drops under 600 meters (2,000 feet). Pilots must rely on autopilot for landing and take-off when visibility is below 550 meters (1,800 feet).
Fog can be removed through artificial dissipation methods such as seeding with salt particles, downwash mixing using helicopter rotors, and heating the air near landing strips. However, these techniques only provide short-term relief under limited conditions.
