Why does fog and mist affect flights?

A number of flights to and from the UK and parts of Europe were delayed or cancelled as a result of the misty conditions. But how are aeroplanes and other aircraft affected by fog?
Foggy conditions can have a severe impact on flights. Picture: PAFoggy conditions can have a severe impact on flights. Picture: PA
Foggy conditions can have a severe impact on flights. Picture: PA

Despite the swathes of technology available to today’s pilots and ground crew, air traffic controllers rely heavily on being able to see the aircraft they are communicating with.

The Visual Control Room, an integral part of every air traffic control tower, allows controllers to guide planes through the airport more easily.

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However, heavy fog and misty conditions can hamper the controllers’ efforts to physically see the aircraft, with the rest of the airport sometimes becoming completely invisible from the control tower.

In the past, this has caused incidents, such as the Tenerife airport disaster in 1977 - the world’s worst aviation disaster.

In foggy weather, air traffic controllers switch to radar and implement ‘low visibility procedures’ in order to carry on operations safely, says NATS - the main air navigation service provider for the UK. The procedures affect aircraft on approach and departure, as well as all movement on the apron.

Additionally, all aircraft use the Instrument Landing System, or ILS, at the airport, in order to be guided automatically to the runway.

With planes following the ILS all the way to touching down, air traffic controllers must ensure there is no interference to the system.

As a result, the ‘spacing’ between aircraft needs to be increased, with each individual aeroplane needing a clear runway for landing and taxiing away from the runway.

According to NATS, poor visibility can lead to the ‘spacing’ between aircraft increasing by up to 50 per cent, whether flights are landing, taking off or taxiing.

It is this need to increase ‘spacing’ that can have a knock off effect at busy airports and hubs, with flights needing to adjust to the conditions.

Tenerife airport disaster 1977

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The Tenerife airport disaster in 1977, resulting in the deaths of 583 people after two Boeing 747s collided on the runway, was partly caused by heavy fog.

KLM Flight 4805 and Pan Am Flight 1736 had been diverted after a bomb explosion at Gran Canaria Airport. The two planes had taxied onto the runway and were awaiting clearance to take off.

The two aircraft were unable to see each other in the heavy fog, with the air traffic controller communicating with the planes unable to see where each plane was, and was instead relying on voice reports due to a lack of ground radar at the airport.

As a result of ‘limitations and failures in communication’ and ‘pilot error’, the KLM flight attempted to take off while the Pan Am flight was still on the runway, resulting in a collision.

All 248 passengers and crew on board the KLM flight died along with 326 passengers and nine crew members on the Pan Am flight.

A total of 61 people, including the pilots and flight engineer on board the Pan Am flight survived.