Someone earlier on quoted the example of train services operating using total automation. With a train, this is suprisingly easy. The DLR is a good example of this. You have one train which runs on one track. You can program the train to stop at certain points along the route. Even here, however, there is a trained staff member on board who can stop the train.
However, with aircraft there are far too many variables. For totally automated flight without pilots, we would have to redesign just about everything in our aviation system. Firstly, taxiing from the gate to the runway is difficult. Either every plane would have to be totally automated and interconnected or none at all. Any plane that did not exactly follow the taxi instruction, messes your whole system up. Then there is evaluating issues like Rejected Take Offs etc. The only computer powerful enough is the brain. End of. To be able to compute information in that time requires excellent situational awareness and experience.
Then of course, when airborne, how do you negotiate with weather systems? The TCAS is simple enough but the weather is one of Mother Nature's biggest variables. Then there are fuel issues. The nearest alternate is simple enough, when talking geographically. But you have to evaluate issues like runway length, weather conditions, company facilities, passenger comfort. Again, only a human can make these sorts of decisions.
On approach, how does the computer know when the approach requires aborting and going around. Sure, these occurences would be less common but when you have so many computers interconnected, if something happens to one plane, it will require something else to happen to another to ensure safety. The Artifical Intelligence (AI) involved works off rules. For the flying to measure up to that of a real pilot who may just be operating the systems, the rules would include a hell of a lot of "IF" statements and also quite a few contradictions. There would doubtless be a Catch 22 situation somewhere within the rules.
You cannot phase in AI planes because for it to work, every single aircraft worldwide needs to be interconnected. (For those who doubt this, think about Microsoft Flight Simulator with a traffic add-on. The aircraft are programmed to do specific things but YOU are the unknown in the equation. The amount of mess you cause by not doing everything the computer tells you shows that without every aircraft automated, the whole AI would fail). For a plane to work without pilots, it would have to work without ATCOs (again variables beyond the intelligence of computers). Also, the second anything outside of normal flight happens, the computer is completely stumped.
The immense number of man hours required to create the level of AI required would make any cost saving almost non-existant. You'd also need to replace or upgrade every single aircraft worldwide to ensure that they could all cope with the technology. Imagine the expense.
Even if you just flew with one flight crew member, what if he/she fell ill or needed a second opinion. The idea of having two pilots is to monitor each other. If someone messes something up then someone else is there to rectify it or point it out. If you had one crew member then nothing would happen. You would end up with the error being carried forward therefore detracting from every other decision made until the end of the flight.
I will present my final argument against automated flight which I use all the time. Would YOU let your kids get on a plane without a pilot?
Automation is here to stay and will affect the lives of pilots worldwide but it will never replace us. The unknowns and variables of flying require a human brain to compute them. Sure, the systems will become more advanced and the job of the pilot will be reduced further into the realms of systems monitoring but the pilot must be there to take control. We are now running a skeleton crew of two flight deck crew, it cannot be reduced for safety reasons. The second an idea like this was put infront of the FAA or EASA, no matter the charisma or charm of the Irish Bullyboy presenting it, whoever proposed it would be laughed out of the room.