FAA flight plan plus an IFR clearance is basically a script. Before autopilots, the pilot followed that script, without radar, with waypoint and next fix ETA reporting by radio. And it has a fallback in place for lost communications, the flight is expected to fly and land at its destination per it's clearance (or most recently amended version of it). And the fallback also includes the possibility of being unable to land at the destination, and instead having to go to the specified alternate in the flight plan. http://delta.jepptech.com/jifp/help/Images/FAAFlightPlan.gif