Fog at Canberra airport

Fog at Canberra airport Photo: Jay Cronan

With an average of 21 fog days over the winter months, passengers flying in and out of Canberra are familiar with delays due to the heavy mists that make it almost impossible to safely touch down.

Visibility was down to 150 metres at the Canberra Airport on Tuesday morning, with flights delayed for several hours. The thick fog was impacting flights until 11.30am.

So while airlines might not be able to control the weather, with support from Airservices Australia, airports, and the Bureau of Meteorology, they can still sometimes land a plane in pretty poor conditions.

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Last year Airservices Australia upgraded the Instrument Landing System (ILS) at Canberra Airport, to keep up with technology that is constantly advancing. It's not a safety system, nor does it guarantee a landing, but a spokesman for Airservices said it helps increase the probability a plane can get close enough to the runway for a pilot to visually see the path for a safe arrival.

Pilots can pick up the ILS signal from about 18 kilometres from the runway. It shoots out both a vertical and a horizontal or lateral radio beam, which then shows the plane's flightpath like a crosshair on instruments inside the cockpit.

"The pilot needs to keep that crosshair in the middle to make sure he or she is on the glide path and on the localiser - they're the two components, a glide path, which is vertical, and a localiser, which does the lateral guidance to the runway," the spokesman said.

At its current level, the category one ILS at Canberra Airport allows a plane to get to about 100 metres above the ground (a distance known as the minima), at which point the pilot must be able to see the landing path.

"Depending on a number of factors for example, terrain, length of runways, all sorts of things, determine that critical height at which the pilot has to make a decision," the spokesman said.

"If the pilots can't see the runway at that level, that's when they execute a go-around manoeuvre, and have another go. Or, if the fog is that bad or it hangs around all day or all afternoon or whatever the case may be, the pilots return to their departure airport or divert to another airport."

Pilots must be trained to perform a landing using the ILS, and runways must have sufficient lighting to aid with visibility. Since the upgrade last year, the ILS at Canberra is capable of performing a category two landing, with a closer minima still, but the advancement would take more work between the airlines, airport, and Airservices.

In parts of Europe where fog is more frequent, thicker, and airports are busier, a category three ILS can perform a hands-off landing for the pilot. But in Canberra, where there is an average of eight fog days each month in May, June and July, and five in August, there isn't demand for such an advanced system.

The category one system currently in place is used daily, even in fine weather conditions, and will continue to provide an aide to incoming pilots trying to land in unfavourable conditions – but it can't prevent delays altogether.

"Where the fog is 50 metres, or you can't even see the end of the bonnet of your car, you can imagine what it's like for a plane flying in the sky. No matter what instrumentation that you have in those conditions that unfortunately Mother Nature serves up, it's very likely, as Canberrans well know, that there's going to be a delay," the spokesman said.

"That's totally out of our control. We can control a lot of things, but one thing we can't control is Mother Nature."

"The fact that an airport has an ILS doesn't guarantee that the planes will land 100 per cent of the time. It improves the predictability of making a successful landing ... If an airport doesn't have an ILS and pilots cannot visually see the runway, then they simply can't land."