- With the growth of civil aviation traffic capacity, safety and environmental considerations urge today for the development of guidance systems with improved accuracy for spatial and temporal trajectory tracking. This should induce increased practical capacity by allowing timely operations at minimum separation standards while at takeoff and landing and trajectory dispersion should be reduced, resulting in better controlled noise impacts on airport surrounding communities. Current civil aviation guidance systems operate with real-time corrective actions to maintain the aircraft trajectory as close as possible to a space-indexed planned trajectory while the flight management system copes indirectly with overfly time constraints. In this paper, the design of new longitudinal guidance laws is considered so that accurate vertical tracking is achieved while overfly time constraints are satisfied. Here, distance to land is adopted as the independent variable for the aircraft flight dynamics since it is today available onboard aircraft with acceptable accuracy. A representation of aircraft longitudinal guidance dynamics is developed according to this spatial variable, and a space-indexed nonlinear inverse control law is established to make the aircraft follow accurately a vertical profile and a desired airspeed. The desired airspeed is defined by an outer space-indexed control loop to make the aircraft overfly different waypoints according to a planned timetable. Numerical simulation experiments with different wind conditions for a transportation aircraft performing a descent approach for landing under this new guidance law are described. The resulting guidance performances are compared with those obtained from a classical time-based guidance control law.