Fogs, Airports, and what really happens

Published: April 10, 2019


The problem of the presence of fog clouds does not end in the reduced visibility of the pilots handling an aircraft, but it extends to the work of Air Traffic Controllers (ATCs). During a fog, pilots are unable to see the runway and ATCs are unable to see what is happening ON the runway. Fog is a low lying cloud with their water vapour coming from nearby bodies of water that condense on dust, ice and salt to form clouds. When visibility is less than 5 km but greater than 1 km with humidity of at least 70%, this fog would be deemed as ‘mist’ while visibility with humidity of less than 70% is considered as haze.

Fog plays an effect on aircrafts during taxi, take off and landing often making it impossible for aircrafts to leave the airport. However, what really happens on land when a fog rolls in? What measures are taken to minimise these effects as much as possible?

During low visibility scenarios, airports are required to reduce the number of aircrafts moving around the airport at the same time as aircrafts must be spaced out up to 6 miles between two aircrafts. This causes major delays and flight cancelations. In areas such as the London Heathrow airport, areas with less ample space than other airports, having to space out aircrafts are a major problem and hence causing chaos.

In the Auckland Airport, there is a system called the Instrument Landing System (ILS) that sends out a signal to guide the aircraft towards the runway during fog seasons. Along with the ILS, aircrafts are also guided by lights on the runway and the ATC. Aircrafts are not allowed to take off without clearance from the ATC which involves a specific form of words that would prevent misunderstandings between the ATC and the pilots of the aircraft, preventing what happened between the KLM flight 4805 and Pan Am flight 1736 on March 27, 1977 (Find out more here:[link]).

With fog, driving and flying would be difficult, but unlike driving, aircrafts have Instrument Rating that allows pilots to navigate the aircraft even without any vision. With the help of the Air Traffic Controller and the Instrument Rating, the aircraft will be able to return back to land with no trouble.


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