Visibility Problems for Flights: Fog vs Smog

Both fog and smog can cause visibility issues for flights, but they do so in different ways. This article investigates how these atmospheric conditions affect the take-off and landing phases of flights, providing a detailed understanding of the risks and the measures taken to ensure safety.

Understanding Fog and Smog

Fog is a meteorological phenomenon characterized by water droplets suspended in the air, significantly reducing visibility. Dense fog can reduce visibility to less than 1000 meters, making take-off and landing phases particularly challenging. On the other hand, smog is a type of air pollution resulting from the mixture of smoke, fog, and chemical pollutants. While it can also reduce visibility, its effects vary depending on the concentration of pollutants and weather conditions. Smog is more common in urban areas and typically does not reduce visibility as dramatically as dense fog.

The Effects of Fog on Flight Visibility

Fog tends to cause more severe visibility problems for flights during take-off and landing. This is because fog can lead to very low visibility conditions, which can be particularly problematic when pilots need to see the runway clearly. The formation of fog is often due to warm air coming into contact with cold ground, causing moisture to condense into a thick, foggy layer.

Understanding Smog and Its Causes

Smog is a complex atmospheric pollutant, often hanging over industrial cities and resulting from a combination of smoke particles and chemical pollutants. The name "smog" comes from the combination of the words "smoke" and "fog." Despite the widespread observation of smog, there is no single agreed-upon definition of what it is. This uncertainty does not negate the need for action to address this environmental concern.

Impact on Aviation Safety

The impact of visibility on flight operations cannot be overstated. Pilots must ensure that they have sufficient visibility to safely take off and land. For pilots operating for personal or business purposes, there are no minimum visibility restrictions for take-off. However, for hired pilots, take-off minimums are based on various factors, including the number of engines, the size of the runway, and the type of runway lighting available.

Visibility Sensing Devices at Airports

Modern airports have visibility sensing devices that report the present visibility in the runway general area. These devices measure visibility in meters or feet, using transmissometers mounted alongside the runway. A calibrated beam of light shines from the transmitter to a receptor, and any obscuration reduces the intensity of the light received. This information is then converted into visual range, providing a clear measurement of the air conditions.

Considerations for Approach Visibility

On a precision approach, pilots rely on the Instrument Landing System (ILS) to guide them as they descend. It is crucial to know what is visible straight ahead, as visibility can vary in different parts of the approach zone. The decision altitude on a precision approach is a critical point where pilots must see the required runway or surface references to continue the approach. On a non-precision approach, the situation is more challenging, as pilots must visually identify the runway during a last-minute "scud run" if conditions are not ideal.

The Importance of Safety Over Risk

While general aviation pilots have the freedom to accept some additional risk for greater utility, it is essential to balance this freedom with safety standards. If all pilots operated under the stringent safety rules of major airlines, general aviation safety records would indeed improve, but this would also lead to the cessation of general aviation as we know it. The goal is to ensure a balance where pilots can operate safely while still meeting the necessary standards.

Conclusion

Both fog and smog pose significant challenges to flight visibility, but their impact differs in severity and prevalence. Understanding these conditions is crucial for ensuring the safety of air travel. By leveraging modern technology and adhering to strict safety protocols, airports and airlines can mitigate the risks associated with reduced visibility, ensuring safe and smooth air travel.