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The current Air Traffic Control (ATC) system relies heavily on voice communications between air traffic controllers and pilots to relay control instructions and other information critical to safe and expeditious flight. These communications are required to support coordination of aircraft movement in all phases of flight, to ensure aircraft separation, transmit advisories and clearances, and to provide aviation weather services. As air travel continues to increase, controller-pilot communication has increased to the saturation point during peak traffic periods at many locations.

Imagine the voice communications link between controllers and pilots as essentially a conference call, with the controller and all pilots flying within an assigned piece of airspace talking over the same channel. Have you ever been on a conference call where two participants spoke at the same time? Neither of them knew that they were interfering with the other participant's speech and it likely took additional conference call time to sort out who heard what and for participants to make another attempt to be understood. You also may have noticed that the interference problem increased as more and more active participants joined the conference call. This is very similar to the ATC voice communications situation in congested airspace. It is not unusual for pilots to key their microphone and accidentally "step on" the communication of other pilots or a controller. This wastes more time on the ATC voice channel as repeated attempts to communicate are made. As air traffic continues to increase, this problem will only get worse. Each voice radio exchange takes a certain amount of time for the originator to transmit and the receiver to respond and there is a point of saturation where a controller physically cannot fit in any additional voice radio communications. At this point, no additional aircraft can be handled within the controller's assigned airspace.

Figure 1: Minutes of Radio Occupation

Controller Pilot Data Link Communications (CPDLC) supplements this vital communications bridge between controllers and pilots. It helps off-load routine, non-time critical exchanges (e.g. handoffs) from the voice channel to a data channel, freeing the voice channel for time critical communications such as vectors around weather or traffic. In high fidelity human-in-the-loop simulations conducted at the Fedearl Aviation Administration's (FAA) William J. Hughes Technical Center, the voice channel occupancy was decreased by 75 percent during realistic operations in busy en route airspace (see Figure 1). The net result of this decrease in voice channel occupancy is increased flight safety and efficiency through more effective communications between controllers and pilots, with fewer missed, repeated, and misunderstood communications.

CPDLC opens a new way of communicating and will enable the introduction of a new paradigm for air traffic control that will alter the way air traffic is managed from pre-departure through landing, breaking free of the voice frequency congestion bottleneck. The FAA has committed to implementing CPDLC nationwide by 2005 as part of its Free Flight Phase 2 program and has outlined its plans in its NAS Operational Evolution Plan.

CAASD's Role

"FAA is absolutely committed to deploying Data Link. It is something we see as really a critical piece of modernization. Raising the bar in aviation safety is a challenge for us, but we know we won't achieve it unless we modernize the system. And Data Link is a critical and key lynch pin, if you will, to the whole effort." Jane Garvey, Former Administrator, FAA

The MITRE Corporation's Center for Advanced Aviation System Development (CAASD) has been a leader with every major advance in air traffic control in the past and will continue to push the envelope and lead the way to solving our future air traffic management challenges. As the FAA's federally funded research and development center, CAASD has over 35 years of experience in designing and developing aviation systems. This depth of experience uniquely qualifies CAASD to help lead the efforts to implement CPDLC as an operational capability. CAASD's leadership role in developing many of the FAA's recent advancements includes:

• User Request Evaluation Tool (URET)
• Converging Runway Display Aid (CRDA)
• Oceanic In-Trail Climb
• Pre-departure Clearance (PDC)
• Traffic Alert and Collision Avoidance System (TCAS)
• Aeronautical Telecommunications Network (ATN)

Current Efforts in CPDLC

CAASD is contributing to the advancement of ATC communications by playing critical roles in the definition and implementation of CPDLC. Because of our overall knowledge of air traffic control, we are working with all of the organizations involved with implementing CPDLC to ensure that each one's contributions fit together and that the interdependecies of each piece are communicated and addressed. This includes helping the FAA to coordinate multiple industry activities (e.g., Preliminary Eurocontrol Test of Air/Ground Data Link (PETAL IIe), ARINC, Rockwell Collins, and American Airlines) with FAA testing activities as well as identifying and mitigating risks through system engineering activities. CAASD also is applying this knowledge of the overall system to allocate and derive key requirements for ground system implementation, including the assessment of overall information security risks and mitigation strategies. As part of the effort to assess the benefits delivered by CPDLC services, CAASD is working with the aviation community to define performance metrics and evaluation methodologies and evaluating the implications of integrating multiple tools from both procedural and technical aspects. To help the FAA and industry stakeholders address certification concerns in a timely and cost effective manner, CAASD is leading a group of FAA Designated Engineering Representatives formed to provide early review and feedback on certification concerns as the FAA and industry develop parts of the CPDLC system.

Implementation

Implementing CPDLC is a joint effort between government and industry, with capabilities being phased into ATC operations incrementally. Achieving benefits from CPDLC depends on both the government developing the required ground infrastructure and aircraft operators voluntarily equipping and using CPDLC. The first phase of implementation in the United States is scheduled to start in the Miami en route airspace in June, 2002. This phase, called Build I, will include the following services:

• Altimeter Settings
• Transfer of Communications
• Initial Contact
• Menu Text (predefined informational messages).

Build IA will follow approximately 18 months later and begin a national roll-out of Build I services plus the capability for controllers to up-link clearances (altitude, speed, heading, and route) and for the pilot to down-link requests for specific flight levels. When the national implementation of the ground infrastructure is complete in 2005, much of the routine controller-pilot communications with CPDLC-equipped aircraft could be moved from the voice to the data channel, freeing up valuable voice frequency time and reducing the impact of traffic growth on voice frequency congestion.