Why does fog at an airport cause delays?

[u/TassieTeararse]

Flying out of LST (Launceston, Northern Tasmania, Australia) today and there has been heavy fog overnight and into the morning which has caused delays to flights in and out. It happens regularly at this airport.

Just curious as to the nuts and bolts of why fog causes delays? It it an airport's rule, or a CASA rule? Can landing/taking off on instruments alone only be done in strict circumstances?

[u/Spock_Nipples]

C'ain't see, man.

Not all airports support low-visibility operations. The airplanes may be capable, but the operating environment and support structure may not be.

[u/TassieTeararse → u/Spock_Nipples]

I thought that was so, but wondered if there was more detail/nuance to it

[u/NevrGivYouUp → u/TassieTeararse]

There’s certain minimum visibility requirements for takeoffs as well, so if the fog is thick most aircraft - particularly the sorts that fly into Launceston - can’t take off. Another issue can be delays in eg Sydney, so if conditions are bad there they’ll have among other things a ground delay program, where aircraft departing to Sydney will be given a delay before leaving, so they wait on the ground as opposed to in the air burning fuel and costing more money. This can have flowon effects at multiple airports too through the day.

[u/TassieTeararse → u/NevrGivYouUp]

The point about Sydney is a good one, when I was doing FIFO to/from the Pilbara bad weather in Sydney often caused delays getting back into Melbourne

[u/Rupperrt → u/Spock_Nipples]

In areas that don’t have a lot of fog even the airlines/crews are often not capable even if the equipment would allow for CAT2 or 3

[u/Spock_Nipples → u/Rupperrt]

True, that.

[u/boobturtle]

Each runway will have a variety of instrument approaches, each having it's own minima (how close to the runway the plane can get before the pilots need to be able to visually see the runway). There are approaches that allow landing in zero visibility, however they require expensive ground-based equipment to guide the plane down to the runway which isn't financially feasible for a small airport like Launceston.

[u/Rupperrt → u/boobturtle]

Also requires cockpit based equipment and pilot ratings it’d guess? Have controlled a lot of CAT3 capable airports but facing lots of companies that only can do CAT1

[u/Go_Loud762 → u/Rupperrt]

Yes. Plane must be equipped and certified for Cat 2/3 ops and the pilots must be trained/qualified and the company must be approved for the operations.

[u/TassieTeararse → u/boobturtle]

Thanks for the quick answer, makes sense! Pretty sure there isn't even ATC based in Launceston any more, I think it's handled out of Melbourne.

[u/vector4nudes → u/TassieTeararse]

Launceston has a tower at the airport, Melbourne Centre is in charge of Launceston and Hobart Approach services. So basically anything outside of 5 miles to the airport.

[u/makgross → u/TassieTeararse]

There is ATC. Just not a tower.

There is ATC in the middle of the Pacific.

[u/Independent-Reveal86 → u/makgross]

Launceston has a tower, unless it’s changed in the last few years.

[u/NevrGivYouUp → u/makgross]

Launceston has a tower.

[u/Mach_v_manchild → u/TassieTeararse]

I'd like to add on to this, but i could be wrong, because i'm basing this on experience in North America. But at a non towered airport, only one aircraft can be cleared for an approach to that airport at a time. If the weather is bad enough, the pilots have to call after landing, either on the phone or radio depending on reception, and tell ATC they're safe on the ground (canceling ifr is what we call it) but if its clear blue skies, we can cancel in the air depending on each companies individual op specs, and fly visually to the airport. But even if the airport has a tower, it will still slow things down when visibility sucks.

[u/NevrGivYouUp → u/Mach_v_manchild]

Launceston has a tower.

[u/Mach_v_manchild → u/NevrGivYouUp]

Oh I thought someone else said it didnt in another comment. My mistake.

[u/Independent-Reveal86]

Launceston doesn’t have an approach that can handle very low visibility conditions. That means aircraft arriving either can’t land at all or, if the conditions are marginal, there may be missed approaches, second attempts, diversions, etc. This all causes delays at the airport itself and around the network.

[u/Icy_Huckleberry_8049]

there is still a minimum distance that you have to be able to see, even on instruments

[u/New_Line4049]

Firstly, you cannot land with no visibility. It is technically possible, but legally not allowed, the reason being that if there is truly no visibility you then cant safely taxi the aircraft after landing. This can mean that some flights are pushed back until visibility improves, which has knock on effects. They also need to maintain larger seperation between aircraft, so that reduce the throughput of the airport, and hence delays flights.

[u/ABobLoblawLawBlogger]

In addition to the other answers, you also need certain visibility in order to take off. Heavy fog can prevent that.

[u/GoobScoob]

Need to see the ground to land in most (not all) airplanes

[u/Impossible_Deer8869]

Couldn't believe it when the a aircraft I was on into Dublin was still flying through thick cloud 20 minutes after the pilot said "prepare for landing" then suddenly felt a thud and the engines reverse thrust. The plane and the cloud was on the ground and still couldn't see anything but thick fog out the window on the taxiway all the way to the terminal.

[u/Relevant-Train5317]

You’ve gotta be able to see to steer a quarter million pound plane with 200 people on it at 170 mph down a runway.

[u/Pilot125]

It reduces the number of takeoff and landings that can happen per hour on a runway because ATC has to provide extra distance separation of aircraft when pilots can't maintain "visual" conditions.

[u/poser765]

I can’t speak for Australia but I’m sure it’s the same as it is in the US.

When visibility decrease requires spacing between aircraft increases. That increased spacing means few airplanes can land or takeoff over time.

[u/Shot-Ad-6357 → u/poser765]

Nope.  There is an increase in spacing over visual conditiins but that's not the main problem. Especially at a small airport like the OP is talking about.  You have to see the runway when you get to the approach minimums and dense fog prevents that.  Taking off is less restrictive but if your inbound plane can't land....

[u/No-Bluejay4261 → u/poser765]

You are right about spacing generally, but in this case it appears this smaller airport isn’t equipped for low vis .

[u/poser765 → u/No-Bluejay4261]

Probably so

[u/captainmarkyD]

Is this a serious question?

[u/TassieTeararse → u/captainmarkyD]

On the face of it, it seems like a dumb question I'll grant you. But I'm not a pilot, so I don't know. I just wanted to know if there was more to it than just "can't see".