I would like to point out one thing about the remote controlled planes part. If someone can control it from the ground, someone else can control it from the ground. Thus, this would lead to people hijacking a plane through hacking the control system. Perhaps "hack-jacking". You mention the strong encryption, but that will be broken. It always is. It would also incur great costs in research for new encryption systems and implementing those systems every time one is hacked. But then, only one being hacked would be enough for massive destruction, thus defeating the purpose.

You also mention that the military uses this technology already, and you may point out that they haven't been hacked. My response to this is that they have the power to keep technology classified. The public sector would not have this luxury. The technology would be widespread, as I expect it would be implemented for every airline in the nation. Being so widespread, the knowledge of how it works would already be subject to falling in the wrong hands, and private citizens would most likely work on the systems. This adds to the number of people with this powerful knowledge. It would be extremely difficult for the airlines to implement this technology and still keep it a secret.

A ground control system that could take over in the event of a hijacking would be best, rather than relying on one the entire time. Even then, nuclear-launch-control security would need to be implemented. The pilots should be on the plane. Everything else, I agree with.

Response to -Brazil- :
The only thing encryption will protect you against is someone intercepting transmissions. Sure, this is helpful - it protects passwords, prevents spoofing, etc. But what happens when someone hacks into the machine controlling the plane? No encryption there.

The only secure computer is one that's unplugged, locked in a safe, and buried 20 feet under the ground in a secret location... and I'm not even too sure about that one. -- attributed to Dennis Huges, FBI

In short, what I was trying to say is this: There is no computer that cannot be hacked. If the plane is controlled through a computer, that computer can and will be hacked.

And as far as the claim that the actual vunerability is interference... Using frequency hopping or an altered version of it, one can secure the transmission from interference. Frequency hopping is a spread spectrum technology developed by the military and now used in the private sector. It is a "narrowband signal that rapidly hops within a specified range of frequencies. By concentrating all of the RF power into individual narrow band transmissions, it can overcome heavy RF noise in short links." - Breezecom's BreezeAccess II Training Manual. Because of this, frequency hopping has a low probability of interception and jamming/interference immunity.

But let's not argue over the highest point of vunerability. We both agree that the system would be too vunerable, and the plane should not be controlled from the ground.