Why are there delays when it is foggy?
During thick fog, Controllers at airports must work to ‘low visibility procedures’, which enable airport operations to continue safely. They cover approach, ground movement and departures.
Spacing on approach to airports is increased, so an aircraft can land and clear the runway before a following aircraft is given landing clearance. Aircraft are also more widely spaced when manoeuvring or taxiing at the airport, whether they are arriving or departing.
All this means that fewer aircraft can land or depart within a given time, causing delays.