The availability of Flight Management System (FMS) equipment in the modern cockpit offers the possibility of introducing FMS-based routes in the terminal airspace. Introduction of such routes may offer significant workload reduction benefits for controllers and pilots. Terminal Air Traffic Control (ATC) currently relies almost entirely on controller issuance of heading, speed and altitude instructions. Introduction of routes in this airspace presents specific challenges because the routes must be compatible with and support the ATC objectives of separation, merging and spacing traffic. This paper studies some ATC issues and benefits associated with the introduction of FMS routes in the terminal airspace in the current ATC environment. A simple FMS route compatible with an existing constrained arrival flow at Baltimore-Washington International Airport (BWI) is studied through a computer simulation. The study investigates the effect of varying levels of FMS equipage and demonstrates that the use of FMS-based routes facilitates a reduction in controller/pilot communication and a consequent increase in airspace throughput. The study also shows that even in an environment of minimal complexity, the mixing of aircraft with and without FMS capabilities presents certain ATC issues. An operational solution to the issues is presented.