Hand-waving about "people" == "simpler" == "better" aside, read about TCAS.
Humans in the loop are a SPoF if they're there:
1. Solely to read information over a lossy, slow medium like analog radio. Digital data between ground and air systems should be the primary means of comms with voice radio as a backup channel for clarification and stating intent.
2. To flawlessly plan and avoid collisions between dozens of objects moving at high speed in 4 dimensions. Never going to happen. These should be done and verified mechanically, continuously.
Humans should be guiding and assisting mechanical, reliable automation of decision-making rather than playing telephone or doing long division on paper when calculators exist.
They likely mean { X, Y, Z, T } three spatial dimensions and time which are four orthogonal dimensions.
That said, it makes the "moving in" redundant and is shy a few dimensions if you want to go full descriptive phase space diagraming given velocity and acceleration in each spatial dimension are missing.
I suggest you take your objections up with the authors of, say,
A Four-Dimensional Space-Time Automatic Obstacle Avoidance Trajectory Planning Method for Multi-UAV Cooperative Formation Flight
or any number of other similar papers.
Many prefer to think of an objects path as a trajectory in space-time (four dmensions) and for two ojects to "collide" their paths must coincide within that 4-D space within an Epsilon for some value of WTF.
But as ... you yourself ... note above, the planes aren't moving in four dimensions. If time is one of the dimensions, all the planes are doing is existing.
The path of the plane is a static curve in 4-dimensional space, yes.
But the plane is not located at any point in the 4-dimensional space, and the position in 4-dimensional space that it doesn't have is not changing over time. Both of those things are required before you can describe the plane as "moving" within the space.
There is no secret backup time that will allow you to track the plane's hypothetical motion along an explicit time dimension. That's not a thing.
I confess. I literally had no idea what you were intending to convey with those two sentences so I restated alternatively what I intended to convey in the hope it might make clear my position (if that was an issue for you) or that I might learn more from your response.
> Where do you think you're contradicting me?
That's not a thought that I thunk.
Therefore I have no response.
> But the plane is not located at any point in the 4-dimensional space
Every point along the 4D path trajectory of the plane in {X,Y,Z,T} is a literal {X,Y,Z} location of that plane at time T.
> Both of those things are required before you can describe the plane as "moving" within the space.
I certainly did not describe the plane as "moving" within R^4.
> There is no secret backup time that will allow you to track the plane's hypothetical motion along an explicit time dimension.
I utterly fail to understand what you intend to convey here.
Although I note that the actual (not hypothetical) velocity of the plane projected onto the time axis is very likely to be on the order of approximately one second per second.
Humans in the loop are a SPoF if they're there:
1. Solely to read information over a lossy, slow medium like analog radio. Digital data between ground and air systems should be the primary means of comms with voice radio as a backup channel for clarification and stating intent.
2. To flawlessly plan and avoid collisions between dozens of objects moving at high speed in 4 dimensions. Never going to happen. These should be done and verified mechanically, continuously.
Humans should be guiding and assisting mechanical, reliable automation of decision-making rather than playing telephone or doing long division on paper when calculators exist.