Why can't planes fly in foggy days?

In foggy days, we often hear reports that the airport is closed because it is difficult for planes to take off and land. When the water vapor in the lower atmosphere is saturated, the water vapor condensate is suspended in the air to form foggy weather, and the horizontal distance of visibility is less than 500 meters, which is called fog in meteorology. However, the visibility requirement for aircraft take-off is at least 600 meters, and the landing requirement for aircraft is even higher than the take-off requirement. Therefore, for the safety of passengers, the plane will only take off when the weather is seaworthy. Due to poor visibility in foggy days, it is difficult for aircraft to take off and land, otherwise it may cause accidents.

But in bad weather, pilots can use the instrument landing system to guide the plane to land, which is also commonly known as "blind landing". According to the accuracy and landing standards of instrument landing systems, ICAO classifies instrument landing systems into Class I, Class II and Class III. The minimum standard is a blind descent, the horizontal visibility is above 800 meters, and the runway can be seen clearly with the naked eye; The second type of blind descent refers to taking off and landing within the visibility range of 400 to 600 meters; The highest standard is three kinds of blind descent. You can't see the runway effectively at any height. Pilots can only make their own landing decisions and rely entirely on instruments to realize the take-off and landing of aircraft. What kind of blind landing aircraft can achieve what kind of effect is determined by weather conditions, airport equipment support capacity, aircraft technical status and pilot's comprehensive technical level.