Torque2 and ock1f confirm what I have said for a number of years. Aircraft and their systems are getting streetes ahead of ATC in their accuracy and complexity. ATC and avionics/airframe designers are not singing to the same tune, leading to a growing mis-match between ATC requirements and what the aeroplane can actually do. Pilots increasingly have to interpret and convert controllers' verbal instructions into an input acceptable by the computers that fly the aeroplane. Hence the confusion that peppers PPRuNe threads.