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Reducing en route separation requirements and improving
terminal area productivity are the primary objectives of CNS research and development. MITRE/CAASD is supporting the Federal Aviation Administration's (FAA)  Safe Flight 2 program, a cooperative effort between government and industry to develop enhanced capabilities for Free Flight based on the evolving CNS technologies. The program uses Global Positioning System (GPS), Automated Dependent Surveillance-Broadcast (ADS-B), Flight Information Services-Broadcast (FIS-B), Traffic Information Service-Broadcast (TIS-B), and their integration with enhanced pilot and controller information displays. Safe Flight 21 will evaluate the safety, service, and procedure improvements these technologies make possible.
Current efforts to implement these systems in the United States have the potential to impact the international system, making "seamless" global air traffic control (ATC) possible. The major enabling technologies
of CNS are:
- Satellite CNS
- Digital datalink
- Precision approach and runway monitoring techniques
Communications
Most air traffic control communications between pilots and controllers
are conducted via voice. In some busy portions
of the United States, such as the Northeast Triangle with apexes at Boston, Chicago,
and Washington, D.C., the system is reaching its limit. Radio frequencies
are congested and new frequencies are not available. This limits the growth
in the traffic to those aircraft that can be safely handled.
MITRE/CAASD is working
with the FAA and airlines to define and test a  controller-pilot datalink capability (CPDLC). Digital data communications between the ground
and the air takes less time and can handle more information than voice communications alone. An important element of the Free Flight concept, CPDLC (Build 1) was implemented at the Miami Center
(ZMA) in late 2002. National deployment of Build 1A is scheduled to begin in late 2005. Build
1A will expand the number of air traffic services that can be conducted via data
link to include altitude, heading, and route assignments.
Emerging collaborative-decision processes, especially those in traffic flow management being investigated in MITRE/CAASD's  Collaborative Routing Coordination Tools prototype, imply new networks and higher bandwidth through which more information can be shared in a timely way. An important dimension of MITRE/CAASD's work in this area focuses on ground-to-ground communications. Controllers in adjacent facilities must be in contact with one another—analysis and development are a necessary function to supporting a decision to
upgrade ground-to-ground communications. Ensuring the availability and security of such communications
systems is critical.
Navigation
Navigation systems are the basis for an aircraft's ability to get from one place to another, know its location and what course to follow. Since the 1930s, aircraft have navigated by means of ground-based beacons, each broadcasting on its own frequencies.
There are several reasons why researching alternate methods of navigation is desirable. The beacon system of navigation constrains aircraft to fly from one beacon to the next, possibly traveling a greater distance to their destination than necessary. Also, because this is a ground-based system, navigation across the ocean and in some mountainous regions also is problematic. Finally, beacons are expensive to maintain.
The navigation system of the United States is evolving towards a satellite-based system and MITRE/CAASD is helping. Based on the Global Positioning System (GPS) satellite constellation, satellite navigation (SATNAV) provides better position information than does the beacon system; and because it is universal, there are no areas without satellite signals. As part of our SATNAV research, MITRE/CAASD analysts are providing the modeling necessary to understand the effects of atmospheric phenomena on the GPS signal from space. We also are working to develop an architecture of the future navigation system and writing the requirements to ensure the navigation system's integrity.
 With the advent of satellite navigation, there are a number of applications that can be piggybacked to increase capacity and throughput in the NAS. Enhanced navigation systems will be capable of "random navigation," treating any latitude-longitude point as a radio navigation fix and flying towards it or away from it with accuracy. New routes into and out of the terminal areas can be proposed which would be navigable by on-board systems, but may be too complicated for hands-on flying. Properly equipped aircraft could then be segregated from other aircraft streams. Such a segregation has the potential to increase throughput at the nation's busy airports by keeping the arrival and departure queues full and fully operating.
Surveillance
Surveillance systems are set up for the air traffic control (ATC) system to know where the aircraft is and where it is heading. In the current NAS, surveillance is achieved through the use of long-range and terminal radars; but information interpolated from the radars is not as good as the position information an aircraft has onboard through the use of satellite navigation.
MITRE/CAASD is working with the FAA and other stakeholders on an onboard automatic dependent surveillance-broadcast (ADS-B) capability that periodically broadcasts an aircraft's position and supporting information, including aircraft identification and short-term intent, more accurately than the current radar capabilities.
MITRE/CAASD supports two Safe Flight 21 initiatives, Capstone and Operational Evaluation-2 (OpEval2) , which are testing ADS-B capabilities to enhance safety and airport capacity and throu-put.
 Capstone is focused on enhancing safety in several areas, including situational awareness, midair collisions, and controlled flight into terrain. The program includes the installation of ground infrastructure, GPS-based avionics, and data-link communications in commercial aircraft serving the Yukon-Kuskokwim Delta/Bethel area. In this instance, ADS-B can be used to increase a pilot's situational awareness, particularly important in places like Alaska where aviation is vital, NAS infrastructure is minimal (because of the harsh conditions), and weather changes quickly and in unpredictable fashions.
MITRE/CAASD has been involved in several key elements of the Capstone Program:
- Providing systems engineering and architecture.
- Planning tests and evaluation strategies.
- Building prototypes and operational models.
- Helping evaluate Capstone's radar-like services and system safety.
 Additionally, MITRE/CAASD worked with the Cargo Airline Association and the FAA to investigate using ADS-B to enhance the capacity and throughput of the nation's airports. The objectives for OpEval-2 included the evaluation of the avionics and procedures needed to support operational approval for each of the Cockpit Display of Traffic Information (CDTI) applications used —approach spacing, final approach/runway occupancy awareness, airport surface situational awareness, and departure spacing. Another major objective for OpEval-2 was the evaluation of air traffic controller use of ADS-B information on their ATC displays focusing on these same CDTI applications.
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