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The technology is simple: at any time an airplane's course or behavior is deemed suspicious, the cockpit controls are overridden by the closest Air Traffic Control center (obviously with appropriate authorization) and the plane put into level flight until the situation can be resolved.
The problem with such a system is that it can be hacked. Remotely controlling a plane would require lots of computer software and computer networking, which is complicated and inherently buggy and subject to hacking. Moreover, the government gets its software from private companies who write government software as a revenue stream (rather than for the sake of engineering excellence or technological innovation). Generally speaking, those companies do not tend to attract the best minds in computer science: Silicon Valley and academia do, or even the NSA or Pentagon. It is very rare for someone good at CS to say "hmm, I think I'll move to Ohio to work for Diebold". They say "Hmm, I think I'll move to San Francisco to work for Google," or "I think I'll move to DC to work on crypto for the government".
It's a good idea in concept, but it would be like Diebold voting machines, only with the potential for death and destruction. Alas.