Originally Posted by teh603
The same older systems that cause innumerable near misses each year? You'd figure the insurance adjustors would've forced it through by now.
Do you have an article on the old vs. the new systems? I haven't read it, so what I'm about to say is merely informed speculation.
You brought up GPS, but that system is meant for navigation rather than air traffic control. It would have to be extended at a bare minimum since it doesn't tell you where other aircraft are. That would require a radio communications system, which means licensing a chunk of the spectrum and running the risk of interference. If the unit loses the satellite telemetry, or the telemetry gets too old, it take several minutes to reacquire the data. You also need signals from a certain number of satellites for the system to even work, and the requirement is higher when you through altitude into the mix.
Oh, and if you thought that interference was not an issue with the current system then you may have just created an issue with the new system. A lot of radios take a high frequency signal and convert it to a lower frequency before using it. Even though you're not trying to transmit at that frequency, you are inadvertently transmitting a very low power signal at that frequency. But the very low power doesn't matter very much because of proximity. So you have now created a situation where the aircraft's instrumentation may be dancing around the same frequencies as the passenger's toys.
These issues are, of course, mostly solvable. Yet they illustrate the point that it is not an easy fix from a technical perspective. So those insurance adjustors are probably nervous about the unknowns, and engineers are probably twitching over the prospect of approving a system that has a lot of unknowns.
Then there are the practicalities. These are things like ensuring that future and existing aircraft are supplied with the appropriate equipment, as well as the aircraft control towers themselves. Before that though, you actually need to test the system to ensure that it works as expected. That is costly in its own right. After implementation you have to worry that you took the right things into consideration when designing and testing the system (because sometimes we forget why things are done the way they are).
Please don't treat these things as magic boxes that you can swap at will. There is a lot of physics, engineering, and policy decisions behind them.