Apart from the other factors making life so complicated recently, fog at landing and take-off causes great disruption to commercial aviation. Millions of pounds each year are consumed in extra fuel, and thousands of passengers are inconvenienced, as schedules go awry and aircraft are diverted from their intended destinations. Ways have been sought of getting rid of fog, but only with limited success.
In the period between the wars, the British had great hopes for FIDO - Fog Investigation and Dispersal Operation. The technique involved using petrol burners placed at regular intervals along a runway to increase the temperature and "burn away" the fog.
FIDO worked, but great amounts of heat were required and the practice was prohibitively expensive. To put it in perspective, the required volume to be cleared might be 300 ft wide, 5,000 ft long and 200 ft in height; total clearance of a thick fog from such a volume might require about 1,000 mw of energy - equivalent to the output from a small power station.
Nonetheless, the equipment was installed at many RAF airfields during the war, and allowed military operations to continue in conditions when they would not normally have been possible. But with the return of peace economic considerations became paramount, and FIDO died.
The French aviation authorities resurrected the idea in the early 1960s and called it Turboclair. They used old jet engines strategically located to provide the necessary heat. Turboclair was in use for many years at Orly and at Charles de Gaulle airports, and has been credited with some success.
Chemical methods of fog dispersal were also tried. The theory goes that if a bank of fog is "seeded" with hydroscopic particles, they will absorb water vapour from the saturated air and grow large enough to fall from the fog like raindrops. By removing the moisture in this way, a point is ultimately reached when the air is no longer saturated and a temporary clearance comes about.
It sounds promising but in practice the respite is very short indeed. The clearance is so ephemeral that it is of little operational use and it is difficult, moreover, to ensure that the "hole" in the fog occurs precisely where it is needed, which is along the runway.
For reasons of expense and unreliability, none of these techniques has achieved great operational popularity. Nowadays, efforts to cope with runway fog tend to be concentrated on the development of more sophisticated electronic landing systems - the idea being to allow aircraft to operate with electronic eyes and guidance systems so that it does not matter whether there is fog around or not.