Assessment of terminal RNAV mixed equipage

Airlines continue to acquire or equip existing aircraft with improved and more capable avionics. Improvements such as the flight management system (FMS) allow aircraft to fly preplanned paths with precision. Attempts to take advantage of improved aircraft guidance to make approaches, arrivals, and departures in the terminal area more uniform and predictable are consequently a natural development in air traffic control. The use of area navigation (RNAV) routes is one example of exploiting the current avionics technology to improve/simplify operations. In this study we look at the consequences and implications for arrivals of the fact that not all aircraft are yet RNAV equipped. The interplay of equipped aircraft (that fly the route according to the FMS) and non-equipped aircraft (which must be vectored) was studied in terms of controller technique, controller training and familiarization, controller comfort level, and the resultant impact on the efficacy of the air traffic control (ATC) operation. The effects of specific factors such as variation in turn execution, variation in speed profiles and airspace use were objectively measured. Three arrival routes of increasing complexity were simulated. One complex route was examined using a varying mix of equipped and unequipped traffic at a fixed, steady state rate. Controller in the loop simulations indicate that the percentage of non-RNAV traffic that can be accommodated on a complex arrival route is about 20 percent, and show at the rates simulated, that it was not necessary to segregate equipped and non-equipped aircraft. The simulation results indicate that the tolerance for non-RNAV aircraft may be even higher for simple arrival routes. Other results of the controller in the loop simulations are presented in detail: reduced flying distances, reduced communications workload, reduced fuel burn and reduced variance in the inter-aircraft arrival times can all be correlated to increasing the percentage of the aircraft that are RNAV equipped. These results argue that there are benefits of aircraft flying RNAV routes.