A lot of comments seem to be about spoofing. Remember that there are multiple humans in the loop -- experienced pilots and experienced air traffic controllers -- and multiple levels of redundancy. Pilots have access to barometric altitude, radar altitude, traditional VHF navaids, TCAS-issued resolution advisories (based on directional antennas, not GPS)... in addition to GPS. Air traffic controllers have primary radar and secondary radar in addition to ADS-B information.
You could probably cause a lot more trouble by buying an aviation radio off the shelf and just chatting on the frequency or issuing fake clearances if you want to be a mass murderer.
Ultimately the system comes down to many systems working together, not one stream of commands between two computers.
You could probably cause a lot more trouble by buying an aviation radio off the shelf and just chatting on the frequency or issuing fake clearances if you want to be a mass murderer.
Ultimately the system comes down to many systems working together, not one stream of commands between two computers.