Trains are on tracks. They basically move in one dimension. And the tracks can have (near) contact-based sensors along the way where the exact distance is known. (And in the US, there still is human conducting in a lot of the US)
That’s a very different problem space than the three dimension, unattached, space that air traffic moves in.
E.g. On 9/11 ATC had to land almost 3000 planes in 1 hour. I'm not sure if that sort of national coordinated grounding is part of ATC training, but it's certainly not something I'd want to leave to some code that has never needed to run in production before.
In your imaginary system how is the software "tower" communicating with airplanes, using voice? I don't think we even have software that can reliably decode the variety of human voices over radio that a controller can respond to.
One can imagine a digital protocol to all airplanes but technology works its way really slowly into aviation.
Planes around airports come in from all directions in three dimensions, and there can be hundreds of arrivals per hour.
These are vastly different scales of problem domain.
In the middle of nowhere. A metro track can have a train every 60s.
But it's still entirely fixed, with easy to deploy sensors on both the tracks and trains.
> there can be hundreds of arrivals per hour
Serious question: Why is 3D such a hard problem for modern computers? I could imagine a plane enters a cylinder of airspace near the airport and automatically communicates by radio waves information about itself. Then, HAL9000 can provide guidance as a landing plan.
And then if you have people flying the planes, you have to deal with people mostly _but not always_ doing the right thing. So now you build out a plan and have to deal with consequences of that.
So at the end of the day you're still looking at funneling humans into a thing. At worst you could consider ATC as "customer support", there to press buttons on machines to actually handle a bunch of logistics because the pilots need to figure things out.
On top of all of this, airports are trying to get through a lot of flights quickly. So people can make snap judgements about whether planes can or cannot advance, what they should do, etc. No matter how well your plan is, the instant a pilot mishears something it's over.
If we can figure out self-driving cars, maybe we can talk about replacing pilots with AIs. But in the meantime there's somebody not following the plan often enough.
This does lead to an interesting question for me, though: what is the biggest "human movement" system that is actually entirely hands-off logistics? I would imagine that postal service companies are doing a lot but every major person moving operation seems pretty hands-on from the outside.
But sure. It’s a mild exaggeration. It still doesn’t change the core point.
3D isn’t just “magically hard” for computers, but the process for routing traffic is wildly complex and a bunch of planes arriving and leaving at semi-random times, directions, and with different requirements and capabilities is where the problem starts not finishes.
The happy path is relatively easy. The exceptions are innumerable.
And ATL is a crazy busy airport (there's an old doc on Netflix I think which is interesting). To confirm your question, ATL can run 5 runways nearly continuously[2]. It would be interesting to know what they peak at during a busy Monday morning, but my guess is they are more constrained by gate space at this point.
[1] https://newatlas.com/us-navy-ouija-board/50087/ [2] https://www.georgiaencyclopedia.org/articles/business-econom...
Maybe I'm getting older. Maybe it is a more modern phenomena, enabled by a steady diet of 30 second videos.
Either way, I'm quite disturbed, regularly, recently, by the # of people who breezily stumble through quarter-baked thoughts while speaking dismissively, as if they've covered the surface of a complex universe that has been worked on very many smart people for decades, and now we can get to the real singular problem that'd fix everything, the one thing they've identified.
I don't even know where to begin trying to interlocute when the starting premise is "3D is hard for modern computers."
So I speak straightforwardly, in a way that I wish wouldn't be seen as rude, but it is.
So it goes.
You're right about the arrivals, but you missed the forest for the trees in the comment you're replying to.
Oh and thousands of lives hang in the literal balance
https://ntrs.nasa.gov/api/citations/19750022064/downloads/19...
>4D AREA NAVIGATION SYSTEM DESCRIPTION AND FLIGHT TEST RESULTS
>A 4D area navigation system was designed to guide aircraft along a prespecified flight path (reference path) such that the aircraft would arrive at the approach gate at a time specified by the ATC controller. Key components to achieve this requirement were:
>(1) stored reference trajectories;
>(2) a continuously recomputed capture trajectory to a selected waypoint on the reference trajectory so as to achieve the desired time of arrival;
>(3) electronic situation displays; and (4) a control system to follow the overall trajectory in space and time.
https://ntrs.nasa.gov/citations/19750015477
>Four-dimensional guidance algorithms for aircraft in an air traffic control environment
>Theoretical development and computer implementation of three guidance algorithms are presented. From a small set of input parameters the algorithms generate the ground track, altitude profile, and speed profile required to implement an experimental 4-D guidance system. Given a sequence of waypoints that define a nominal flight path, the first algorithm generates a realistic, flyable ground track consisting of a sequence of straight line segments and circular arcs. Each circular turn is constrained by the minimum turning radius of the aircraft. The ground track and the specified waypoint altitudes are used as inputs to the second algorithm which generates the altitude profile. The altitude profile consists of piecewise constant flight path angle segments, each segment lying within specified upper and lower bounds. The third algorithm generates a feasible speed profile subject to constraints on the rate of change in speed, permissible speed ranges, and effects of wind. Flight path parameters are then combined into a chronological sequence to form the 4-D guidance vectors. These vectors can be used to drive the autopilot/autothrottle of the aircraft so that a 4-D flight path could be tracked completely automatically; or these vectors may be used to drive the flight director and other cockpit displays, thereby enabling the pilot to track a 4-D flight path manually.
https://www.airbus.com/en/newsroom/stories/2020-12-4d-tbo-a-...
>4D-TBO: a new approach to aircraft trajectory prediction
>How four-dimensional trajectory data could contribute to aviation decarbonisation targets
>The real-time transmission of four-dimensional trajectory data has the incredible potential to greatly improve an aircraft’s trajectory prediction. By reducing the inaccuracy of current air traffic management (ATM) prediction models by approximately 30-40%, the Trajectory Based Operations in 4 Dimensions (4D-TBO) project is helping to pave the way to a more sustainable management of tomorrow’s air traffic.
https://skybrary.aero/articles/4d-trajectory-concept
>The 4D trajectory of an aircraft consists of the three spatial dimensions plus time as a fourth dimension. This means that any delay is in fact a distortion of the trajectory as much as a level change or a change of the horizontal position. Tactical interventions by air traffic controllers rarely take into account the effect on the trajectory as a whole due to the relatively short look-ahead time (in the order of 20 minutes or so).
>The implementation of 4D trajectory management is being researched by SESAR (Single European Sky ATM Research) in the EU and NextGen in the US.
>The 4D trajectory concept is based on the integration of time into the 3D aircraft trajectory. It aims to ensure flight on a practically unrestricted, optimum trajectory for as long as possible in exchange for the aircraft being obliged to meet very accurately an arrival time over a designated point.
How many options are there for handling emergencies with aircraft now? You pretty much just have either land ASAP or circle to burn fuel and then land.
Ah, there it is. "How hard could coordinating takeoff and landing for thousands of flights be? You just..."
I’ve heard ATC swap landing and takeoff directions in the space of 10 minutes because of weather