JT8DJET has just hit some of the very basics. Every point on the entire operation (not just the maintenance program) must be proven to the FAA. We at DAL have just completed the 'Proving Runs' for the FAA for the new 764s.
We were required to fly many hours of pilot trainers so that the flight crews had proficiency with the aircraft.
The mechanics were required to pass an 80hr initial airframe / systems / avionics course AND a 24hr On-Job-Training class before they are allowed to work on the 400.
The FAA sent representatives with the aircraft on a non-revenue flight. The route was ATL-MIA-LAX-OGG-HNL-ATL. At each stop and enroute, the FAA gave out simulated problems to 'test' DALs procedures. Everything from training records to the manuals was looked at. Flight attendants were given in-flight emergencies to react to. It was a very intense 4 days. All of this even though DAL has been flying -300ERs since they came out in the mid 80's!
(We ARE just a little curious how CO managed to enter revenue service with the -400 before us when they have never flown 767s at all. BUT WE'RE NOT BITTER ABOUT IT NOPE NOT US NOPE NOT AT ALL)
Hope this explains a little more what is involved. If you have specific questions, drop me an email.