Driving in thick fog can be extremely hazardous, and of course you must slow down to ensure you remain safe. But, how does fog affect flying. Surely it’s impossible to land an aircraft at 150mph in thick fog?

Not at all.

Firstly, every aircraft has it’s own visibility rating. This determines the lowest visibility that the aircraft type is permitted to land in.

Also, each airport will have it’s own visibility ‘rules’. An airport reserves the right to close it’s runways at any time if the level of visibility falls below their permitted minimums.

Thirdly, each airline will have it’s own rules that pilots will follow with regards to when they can or cannot land.

Believe it or not – and most don’t – most modern aircraft can land in zero visibility using the autopilot. Now, this sounds scary right? I’m supposed to be helping you with your fear of flying in bad weather, and then I tell you that sometimes we rely on an autopilot to land the aircraft!

The ‘auto-land’ only works at airports that have a specific system installed, called the Instrument Landing System (or ILS). The on-board computers will have the settings installed so that the aircraft knows where it should be at any given point during the landing.

Therefore, the ILS system guides the aircraft in perfectly, even if the pilots cannot see the runway. It works by sending radio signals to the aircraft on a set frequency (that the pilots will ‘tune’ in to before the approach).

The autopilot will read these frequencies and move the aircraft into the exact position that it needs to be in to land safely. The aircraft will continue to communicate with the ILS system until it has landed on the runway, and slowed down.

In fact, the system is so good that the aircraft will land in the centre of the runway 100% of the time – it really is that precise.

Differences you may notice during an autoland are;

1. The aircraft will make contact with the ground quite hard. This makes it feel as though it’s a bad landing – but actually it means it’s perfect. Aircraft are supposed to land this way – but pilots tend to make it a more comfortable experience for you! Do not be alarmed.
2. Braking will be much harder, and the engines will be noisy. Every auto-land will result in reverse thrust being deployed. I will be covering reverse thrust in more detail in the future, but it’s basically reversing the direction of thrust on the engine to slow the aircraft quickly. This means braking will feel much harder, and the engines will roar. It’s a completely normal noise, and nothing to worry about.

I hope that helps. Next time you are coming into land and you ca’t see the ground, don’t worry. The pilots will be using the amazingly accurate ILS system. They will never attempt a landing in low visability without it!

Sometimes the pilots will choose to use auto-land on a clear day. This is not down to laziness, they are simply practising the procedure.