By 2025, U.S. air traffic is predicted to increase 3-fold and may strain the current air traffic management system, which may not be able to accommodate this growth. In response to this challenge, a revolutionary new concept has been proposed for U.S. aviation operations, termed the Next Generation Air Transportation System or "NextGen". Many key capabilities are being identified to enable NextGen, including the use of data-link communications. Because NextGen represents a radically different

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... proach to air traffic management and requires a dramatic shift in the tasks, roles, and responsibilities for the flight deck, there are numerous research issues and challenges that must be overcome to ensure a safe, sustainable air transportation system. Flight deck display and crew-vehicle interaction concepts are being developed that proactively investigate and overcome potential technology and safety barriers that might otherwise constrain the full realization of NextGen. The paper describes simulation research examining data-link communications during 4DT and equivalent visual surface operations. Voice Communications Verbal communication is critical in today's National Airspace System. It's the most efficient and adaptable form of communication and has inherent advantages including speed of transmission, human tone to express urgency and intention, flexibility of dialogue, and provision of party-line or broadcast effect. Pilot-Air Traffic Control (ATC) aural communications have historically been quite successful yet are far from errorfree. One content analysis showed that 40% of ATC-pilot communications contained at least one irregularity [1], but the error rate was less than one percent [2] . Fortunately, 60 to 80% of these errors were caught in the read-back process. However, the proportion of corrected read-back errors varied, where the highest workload sectors had the least corrections: en route controllers corrected 89% of the read-back errors, TRACON and local controllers caught only 60%, and 63%, respectively, and only 50% of the read-back errors on the ground frequency were corrected. https://ntrs.nasa.gov/search.jsp?R=20110003612 2018-07-24T07:35:04+00:00Z Problems with language interpretation, clarity, radio congestion (blocked transmissions), confusion, readback errors, message factors (formulation, packaging, and delivery), and extraneous environmental noise can lead to misunderstandings during voice message reception [3] . Cushing [4] categorized these into groups involving communication problems based on language and those based on non-language. Language-based communication problems include ambiguity, homophony, punctuation, intonation of speech, speech act, problems with reference (including uncertain reference, uncertain addressee, and unclear hand-offs), problems with inference (including implicit and lexical inferences, unfamiliar terminology, and false assumptions), and problems involving repetition (such as no read-back, partial read-backs, ritualization of speech, and cultural issues). Non-language communication problems include issues with numbers (including range overlaps and transposition) problems with radios (including loss of radio and misuse of radios), and problems with compliance (such as distractions, interruptions, fatigue, non-cooperation, etc.). Data-Link Communications The Need. The rapidly decreasing availability of radio-frequency bandwidth is driving a rapid shift from voice to data-link. The EuroControl/FAA Future Communications Study Operational Concepts and Requirements Team stated, "The growth in aviation traffic has resulted in enormous pressure on the ability of existing spectrum resources to satisfy communications requirements. The very high frequency (VHF) spectrum is already congested and will be the significant limiting factor in Air Traffic Management (ATM) capacity by 2015 unless additional air/ground communication sources are made available to supplement the existing system" [5] . By the year 2015, only 60% of communications are projected to be provided via voice during the most critical phases of flight in the Airport/Terminal Maneuvering Area (TMA). By 2030, 85% of Air Traffic Services communications are projected to be provided via data-link in the TMA environments [5]. The Benefits. A key enabler of operations envisioned under NextGen is data-link communications and a voice-by-exception (i.e., data-link for routine communications) airspace environment. Data-link communications are a critical determinant to the expansion of air traffic capacity and to the success of an adaptable, "net-centric" operational capability under NextGen. As presently envisioned, the data-link interface changes the modality of pilot-ATC communications from aural to visual using text read-outs on the Flight Management System (FMS) Control-Display Unit. With this modality shift, research shows data-link communications generally provide the following positive benefits for pilot-ATC communications [6 -13].  Reduction or elimination of message blocking and congestion  Higher efficiency and capacity of communications system resulting in improvement of message delivery time (i.e., when compared to current limited radio-frequency bandwidth, stepped-on messages, and controller-pilot read-back times)  Persistence of the message  Unloaded memory burden from lengthy messages, and ability to review later  Improved information-processing efficiency and accuracy  Possibility of effective multitasking due to user-pacing communication tasks and elimination of continuous listening workload  Ability to enable automatic gating that may improve information transfer to other ATC and flight deck subsystems  Inherently easier and more accurate communications for crews with language and cultural barriers The Issues. While the transition to data-link communications would appear to be extremely beneficial, there are also many issues/concerns to be addressed. Research has shown that: