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How do pilots navigate through the fog?

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."

7 comments

  • Remember that day the fog was so thick that the train couldn't run? Me neither.

    Commenter
    Seems fair
    Date and time
    June 18, 2013, 11:41AM
    • Relying on instruments while flying is OK most of the time...until you feed the aircraft computers the wrong data.
      Who remembers that very, very close call with a passenger jet in-bound from Perth waiting to land at Canberra when the flight crew set the altimeter on the auto pilot too low and passed over rocky Tinderry mountains peaks with 50 meters to spare early one morning in the pre-dawn darkness & clouds.
      On that occasion the on-board warning system alerted them to the solid object looming up in front & they acted quickly enough but only just.

      Commenter
      dusty
      Location
      Terrain..pull up!
      Date and time
      June 18, 2013, 2:06PM
      • Yeah dusty: there's a difference between mistakes you can make just flying around the countryside compared to what mistakes can be made at airports. Airports have "glide slope" signals to guide the aeroplane in precisely. The aeroplane ought to be able to land itself with zero visibility, and in fact taking the human element out of it is probably better in most cases.

        I'm not sure how much fuel is wasted sending aeroplanes back to where they came from 8 times per year, but I would have thought that would pay for an awful lot of better equipment at the airport, so this article seems quite odd to me.

        Commenter
        John
        Date and time
        June 18, 2013, 3:42PM
      • Dusty I am impressed by your technical analysis of the incident, you must be quite an experienced flyer. In fact, I wouldn't be surprised if you stated that you are in fact a silver or even a gold frequent flyer. We could save vast taxpayer dollars by disbanding the ATSB and having you report on these incidents.

        Commenter
        Angrypube
        Date and time
        June 18, 2013, 8:24PM
    • Let's remember that most heavy jets will use this and other auto-pilot technologies nearly continuously during the flight. Auto-pilot coupled to the ILS will be used for most approaches anyway, even in clear whether, because the plane can fly a smoother and more precise approach. Hands-on is really only for take-offs and landings, and even landings are still supported by technology eg. go arounds are pre-programmed so that they can be performed at the touch of a button.

      So, we should be confident about the technology - it's in nearly constant use.

      Commenter
      AS
      Location
      Geneva
      Date and time
      June 18, 2013, 5:29PM
      • I'm confused, or maybe the journalist is. He writes that in Europe "hands-off" landings are possible, but apparently in Canberra they never will be, regardless of upgrades. Which is true? I think 29 days of disruptiona year is significant, and so too do the politicians and others affected by it.

        Commenter
        IrishPete
        Date and time
        June 18, 2013, 6:15PM
        • It must be more than an average of eight days. As a Canberran, we definitely get more than that

          Commenter
          Dalek
          Date and time
          June 18, 2013, 6:18PM
          Comments are now closed

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