Today is foggy and a lot of the airports in this area have delays because of it. Is this really a problem in this day,with radar and other landing aids, or is this a case of safety first ?
Are you suggesting safety be 2nd ?
Things may have changed since I knew about this, but it used to be that, even though nav aids are really sufficient to land and take off a plane, it was forbidden except in emergencies (such as low fuel and no alternate airport).
You have altitude readings, the problem would probably be that Radar can’t guide you to within 30cm of the centre line of a runway
Some suitably certified ILS systems can be used in very low visibility conditions and will allow the aircraft to land “automatically” - I put that in scare quotes because I’m told it’s a PITA to set up and most pilots of these aircraft would rather just land the damn thing by hand if at all possible.
Of course, such a procedure requires aircraft and runway to have suitable equipment, and not all do in either case. Aircraft which can’t perform that procedure are going to have to wait until things improve to within their limits or possibly go somewhere else.
My own local airport (IANAP, just a geek) gets foggy quite a lot. Another problem they have is moving aircraft around the ground. They have to be a lot more cautious when they can’t assume that the pilots can see other planes.
Hold on, planes can land themselves? Why do we have pilots at all?
Also, Die Hard 2 shows why planes don’t land in fog
Airport fog always make me think of the Tenerife airport disaster, the deadliest incident in aviation history other than 9/11. Although there were numerous other factors involved, fog played a significant role in the accident that killed 583 people.
Not being an airline plane, I took off from Cape Girardeau, Missouri one morning in Zero - Zero conditions.
Was running round in a Aerostar 601, ( light twin engine piston engine ) which has pretty low to the ground pilot seats.
The airport is in a valley next to a river. Fog deluxe. Walking, I could barley see my feet. Really strange feeling. I did find the airplane and since we had fueled the day before, all I needed was to leave.
Long story short, filed IFR to VFR ‘on top’ and on to Tulsa if need be. All weather said the rest of the world was clear. Just not down in this particular hole. I could see about 3 feet, yes, three feet past the nose so I could see about 3 feet of the taxi stripe. “That will work.”
Got the clearance and the Tower said to have fun as they could see nothing. I just used the airport diagram since I knew where I was starting from and followed the yellow lines to the runway just fine. A little slow but there was no other traffic. Bawahahaha
I lined up on the center stripes and my passenger, an Ex- active Marine vet from Nam. ( this was in 1989 or 1990 ) and had him up front beside me and told him his job was to watch the stripes and to tell me if I was moving left or right of it either way as I had to start out using only the instruments as soon as we were doing about 30 MPH or so. I had to be rock steady on the gauges before we left the ground.
Only danger was if we had an emergency before we were clear of the fog that made us unable to climb. Then it was ‘dead ahead to what ever is out there.’ He/we thought the need to go was worth the gamble using all I knew about the plane and what I could do as a pilot. (All perfectly legal at that place and time.)
Off we went and we broke out on top before the wheels were fully retracted. About 300 feet above the ground.
Reported that Wx to the tower and KC Center who I had just contacted and then dropped the IFR flight plan and had a great run into Tulsa.
A few years earlier, in a Cessna-180, I had some bad Wx forecasts and some lack of lights at one place that was not ‘NOTAMed’ out so pilots could learn about that, which all together caused me a chilling landing near a lake in Iowa. East of Des Moines a fair bit.
There is some, 'I shoulda ’ & ‘I wish’ scattered through that flight
That is a tale for another time.
Not stealth bragging or anything, just showing what can be done in other than airline flying. There safety is # 1 all the time where as in many other flying jobs, more risk is taken in order to get it done.
Small plane flying in Alaska will blow your mind at what they can do and will do and will try to do. People die when things go wrong and much can be avoided with safety of flight before other emergency situations. Some times the added risk is small enough to become secondary to other considerations.
Of course people die when they calculate wrong.
Even more than in airplanes. ‘I thought’ kills many auto drivers when it could be done another time or in less of a hurry, etc…
I am an old pilot now and hardly ever can afford to fly but, when I do, I still can do. 
.
GQ is not the place to be citing “Die Hard 2”…
Planes have been able to land themselves for decades, as long as both the airport and the plane has the right equipment.
All I know is that autolanding is not something that happens frequently, or at all really.
At some point the pilots need to be able to see the runway to put down the plane.
That isn’t true in the least. It is quite common and, if you fly the airlines fairly regularly, it is extremely likely that you have been on a flight that used that capability either because of weather or as a certification check for the aircraft. Aircraft equipped with auto-land capability have to demonstrate it at least once every 30 days to maintain currency.
It is true that most pilots prefer to do manual landings as long as the weather permits it but it isn’t true that “that autolanding is not something that happens frequently, or at all really.” It gets used regularly on all the airliners that are certified for it and is required for some weather conditions and to maintain currency.
Is there a list of airports that support autolanding?
Tons of aiports support CAT I/II/III instrument approaches, but the lists of US Airports approved by the FAA for CAT II and CAT III Autoland or HUD-to-touchdown is pretty small. As of 2014, those airports are:
CLE (Cleveland)
CVG (Covington, KY)
DEN (Denver)
BNA (Nashville)
PIT (Pittsburgh)
SEA (Seattle)
I would imagine the wind would remove the possibility of an automatic landing quite often @Sea (IANAP).
Even if the airport does support auto-land, everything slows down because no one can see on the ground so the number of aircraft allowed to taxi at one time is limited. Also the areas around the ILS antenna have to be “protected” which means aircraft can’t be allowed to taxi past the antenna while another is on the approach. It reduces the airports movement rate significantly which means delays not only for the airport with fog but also for all of the subsequent flights.
If there is any significant wind, there won’t be any fog. That said, autoland can handle a certain amount of wind. Crosswind is normally the limiting factor. I fly the Avro RJ which has a crosswind limit for autoland of 10 knots (compared to 35 knots for a manual landing) but more modern types aren’t so limited. .
Note that this disaster occurred when both planes were on the ground.
As PaulParkHead mentioned in passing, the danger of fog is mostly on the ground, when planes are taxiing to get into position on the runways or at the terminal spots. Planes are much closer than when in the air, and there is much less room to maneuver then in open airspace. So the ground controllers have to space the planes out more as they move around, thus there is more time between takeoffs or landings, and this delays the whole schedule.
Remember too that there are also*** a lot ***of other vehicles driving around close to the taxiing aircraft. Fuel trucks, luggage trams, safety vehicles etc. are all often crisscrossing aircraft paths in the taxiways. And none of these are going to show up on ATC radar or have any sort of navigation ‘pinging’ devices.
Dorjän’s list in post 13 is woefully inaccurate. Or perhaps is a list of some other criteria for some different purpose. Most US big city airports support autoland for suitably equipped aircraft and suitably certified crews. What only a relatively few airports support is autoland under the very worst visibility conditions.
In general airline airports are equipped for the worst weather they encounter often enough to make the incremental investment in infrastructure pay off. Said another way, an airport having a day with once-per-decade density of fog will probably be experiencing worse fog than their airport is equipped for. So nobody is landing. OTOH, an airport having the kind of fog they get on average 10 or 15 days per year will be equipped for that. So aircraft will be landing.
Going back to the OPs’ specific question:
The maximum rate we can land airplanes at an airport on a sunny day is faster than the maximum rate we can land them on a foggy day. Imagine your normal freeway commute in the morning but with a lane closed for construction. That’s what a foggy day does to a big busy airport. Everything gets backed up. And it is possible for the fog to get so bad that it exceeds the capability of either the airport or of the predominant users. At which point it’s like your freeway after a crash in the construction zone. Nobody is moving until the situation is cleared up.
In addition to the airport needing to be equipped for the weather du jour, so must the airplane and the crew. Different airlines and different aircraft types are equipped for dealing with different thicknesses of fog.
For example, Southwest Airlines is not certified to operate into the foggiest conditions. So they are often grounded when the fog is very dense and other airlines are getting in just fine. Why do they do that? To save money. And for the majority of their airports on the majority of the days of the year that works just fine for them. But once in awhile it bites them in the butt.
The same thing is true of many regional jets (RJs). For similar economic reasons. A downside to this is that if you have an integrated hub where both mainline and RJs are coming in, exchanging passengers, and leaving again, the whole system comes apart if the big jets are arriving like clockwork and the baby jets are all sitting at some out-station someplace awaiting good enough weather at the hub.
At airports with an ASDE-X ground radar (which there are quite a few, I’m on my phone and can’t bring up the list), ground vehicles appear on the controller’s screen. If the vehicle has a transponder (which some do at ASDE-X equipped airports), its information will also appear on the controller’s display just like aircraft do. Even if they don’t have a transponder, they will show up as a primary target in the display.
Even at airports with ground radar, low visibility operations (called SMGCS, pronounced “smigs,” for Surface Movement Guidance Control System) will go into play for visibilities lower than 1200-2400 feet. SMGCS reduces the available taxi routes, reduces runways available, and generally slows everything down.