Comment by contingencies

Fun napkin-view ADS-C ("control"-capable successor to broadcast-only ADS-B).

Reporting integrates approach and flight tunnel envelopes. Envelopes are specified with coordinates, not just sequential points + altitude.

Cryptographic authentication in subsequent position broadcast from plane flight systems efficiently confirms receipt and acceptance of prior control messages.

Flight systems warn on countdown to envelope exception not only actual envelope exception or altitude exception.

For passenger planes, ability of ground control to command autonomous landing with blessing of federal government in an emergency (eg. no pilots conscious, interface borked), and to send urgent, cryptographically authenticated ATC command requests (change altitude or heading immediately, etc.) for pilot consideration in the event of ATC-detected potential emergent danger conditions.