It sometimes surprises visitors to an airport tower just how visual the job is. Controllers in the Visual Control Room are physically looking at the aircraft they’re guiding, with minimal use of radar. The clue is in the name, I suppose!

But during periods of bad weather such as fog, like parts of the UK are experiencing today, the rest of the airport can become completely invisible from the tower.

In these circumstances control has to switch to radar and ‘low visibility procedures’ to ensure airport operations can continue safely. These special procedures cover aircraft on approach and departure, as well as movements on the ground.

A foggy Gatwick Airport by zzathras777 via Flickr

A foggy Gatwick Airport by zzathras777 via Flickr

In foggy conditions, aircraft use the Instrument Landing System (ILS) at the airport to be automatically guided to the runway – they are effectively following the ILS beam all the way to touch-down. It is therefore important that we protect the beam from any interference, such as from other aircraft on the runway.

This means spacing between aircraft has to be increased, with an aircraft having to touch-down and taxi far enough away from the runway such that it no longer interferes with the ILS beam before the next one can be given landing clearance. Typically this means the spacing between aircraft has to increase by up to 50%.

Aircraft are also more widely spaced when manoeuvring or taxiing, whether they’re arriving or departing.

All this takes extra time, effectively taking capacity out of the airport with the end result often being delays to passengers sitting in the terminals.

Whenever there’s bad weather we work very closely with airlines and airport operators to handle safely as many flights as possible and minimise the disruption.

As ever, if you’re concerned about the effect bad weather might have on your flight, you should contact your airline which will be able to provide you with the latest information.

Header image by Christian Steen via Flickr


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“Spacing between aircraft has to be increased meaning an aircraft has to touch-down and clear the runway before the next one can be given landing clearance.”

I should hope that the runway is clear before giving a landing clearance all the time, not just in bad weather.



David Pearson

A landing clearance is not the same thing as putting wheels down on a clear runway. Its effectivel authorisation to proceed with the approach and landing and which is predicated on the runway being clear when the actual landing occurs.



Radha Kurup

Great. I had concern about air travel with radar, auto pilot, etc., as machines cannot take action in an emergency. Only human beings can be alert and take steps necessary for safety of passengers. Also planes are to be taken care of.




The radar can assist to land more aircraft at the same or short possible time depending conditions equipped and LRA but ILS can have interference by but another aircraft on the Apron or on the runway so for safe operation ATC has to has to land or departure aircraft should at least 15 mins or possibly to handle Obe enroute atc before



Andy Thorne

So when it comes to choosing which flights will be cancelled is there a procedure for this? E.g. Is priority given to long haul flights over short haul or chartered over scheduled? Or is just the ones at the back of the queue?

Hi Andy, that’s always an airline decision but usually it is short haul traffic that has to be cancelled first. Paul




Recently a Dutch scientist might have found a solution for this by the use of circular airfields. The article is in dutch but you can read more about it and watch a video on




Wind turbines could have been designed to run as fans in foggy weather to blow the fog away from airports 😉


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