Advances in technology and automation have led to a gradual decline in the number of crewmembers employed in commercial airliner flight decks. Aircraft manufacturers incorporating these new technologies eliminated the positions of radio operators, navigators, and flight engineers by the 1980s, resulting in the current two-pilot model. The commercial aviation industry is poised to make yet another reduction as the aviation industry contemplates the concept of single-pilot operations as the next

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... ogical step. These new technologies are developing at just the right time; as air transport routes expand globally, an industry-wide shortage of pilots persists. Boeing (2018) forecasts a global requirement for over 790,000 new pilots by the year 2037 in order to meet the demand. Reducing crew requirements to single-pilot operations presents a means to alleviate the demand but introduces new technological and human factors challenges. Lim, Bassien-Capsa, Ramasamy, Liu, and Sabatini (2017) described managing and distributing workload, maintaining pilot situational awareness, and interface design as some of the key challenges to implementing single-pilot operations. Bilimoria, Johnson, and Schutte (2014) further detailed the need for automation to change between tasks and roles without being "rigidly prescribed" (p. 6) and function much as an active crewmember. Conceptually, these challenges illuminate the necessity to simplify the user interface, facilitate coordination between the pilot and automation, and simultaneously increase the extent and complexity of tasks to be automated. Statement of the Problem Speech interfaces present a novel opportunity to address the emerging requirements of automation in the single-pilot operation environment. Speech is a simple and intuitive method of interacting with a system, as the interaction is limited by the ability of the system to recognize and interpret the input, rather than by the finite space of controls on an instrument panel. The further step of interpreting natural, spoken words, exemplified throughout the U.S. population in digital assistants in smart phones and smart home devices, such as Apple's Siri and Amazon's Alexa, demonstrated the possibilities of using speech interfaces in existing technology to simplify the interface to complex tasks. While speech interfaces present opportunities to reduce pilot workload overall, they are still considered an emerging technology, especially in aviation. Consequently, there is little research describing what effects such systems can have in the flight deck and in human performance. With increasing automation in the single pilot environment, some form of simplified interface will be required; how speech interfaces compare to traditional mechanical or touch screen interfaces in the flight deck remains unknown.