Why can't airplanes land in fog?

It's also the case that planes cannot fly as close to one another in fog as they do on a clear day - a nice clear day means they can see one another - fog means they can't see one another. If you can't bring the planes as close to one another as usual it means the number of planes that can land on a runway is reduced. read more

May 31, 2013, 9: 27 AM Add to all that, even when they can and do land in fog, for example at Heathrow, the minimum landing times between successive planes is lengthened considerably, so there likely isn't enough time at congested airpots operating to the max, to land all planes, so some have to be diverted. read more