Whenever a new aircraft is going to be put on an air carrier operating certificate, the company sets up a program. The program runs the gambit of protocols for how pilots and flight attendants will be trained, how mechanics will be trained, ground handling, servicing, boarding, evacuation drills, ditching drills.....you get the point.
Then the aircraft is flown with the initial cadre of check airmen. They put the aircraft through its paces and the FAA observes these flights. They do this for several days, then they "take over" and start handing the flight crews "scenarios" which the crew must deal with. It isn't just the pilots they are looking at, but the inflight crew, dispatch, maintenance, customer service....all departments that make up an airline.
The "diversion" to CLT was a scenario where the FAA wanted to see a diversion to a non JetBlue city. CLT was picked because of the weather and the pilots familiarity with the airport.
The company is basically "proving" to the FAA that they can operate the aircraft according to the FAR's and the scenarios prove the validity of the company policies and procedures. These scenarios help the company find the weak spots in their training policies/procedures, their operating procedures, and because it is a new aircraft, help them gain familiarity with it.
Hope that helps.
A350
