21st Century Aviation Innovation, Reform, and Reauthorization Act or the 21st Century AIRR Act This bill reauthorizes and modifies Federal Aviation Administration (FAA) programs. It also establishes the American Air Navigation Services Corporation as a federally chartered, not-for-profit corporation to assume operational control of FAA air traffic services on October 1, 2020. The bill revises requirements for the pilot program for passenger facility charges at nonhub airports and the airport improvement program. The bill extends the authorization for airport development at Midway Island Airport. The Department of Transportation (DOT): shall carry out an environmental mitigation pilot grant program for sponsors of public-use airports; and may make grants to such sponsors for environmental mitigation projects to reduce or mitigate aviation impacts on noise, air quality, or water quality at the airport or within five miles of the airport. DOT shall establish a Safety Oversight and Certification Advisory Committee. The FAA must establish: the FAA Task Force on Flight Standards Reform, a Regulatory Consistency Communications Board, a safety workforce training strategy, and minimum dimensions for passenger seats on aircraft operated by air carriers. The FAA must also issue an order requiring the installation of a secondary cockpit barrier on aircraft manufactured for delivery to a passenger air carrier in the United States. DOT shall take appropriate actions to promote U.S. aerospace standards, products, and services abroad. DOT shall modify regulations regarding flight duty limitations and rest requirements to ensure that: (1) a flight attendant scheduled for a duty period of 14 hours or less is given a scheduled rest period of at least 10 consecutive hours, and (2) the rest period is not reduced under any circumstances. The bill prescribes certain requirements for improving passenger air service. The bill also reauthorizes the essential air service program and the small community air service development program. DOT shall: develop a comprehensive plan to accelerate the integration of civil unmanned aircraft systems (drones) into the national airspace system, establish a regional air transportation pilot program to provide operating assistance and grants to provide and maintain air service to communities not receiving sufficient air service, require each air carrier to submit for approval a one-page document that accurately describes the rights of passengers in air transportation, require large ticket agents to adopt minimum customer service standards, and establish a remote air traffic control tower pilot program for rural or small communities. Each air carrier must submit to the FAA an Employee Assault Prevention and Response Plan related to the customer service agents of the air carrier. The FAA shall review its strategic aviation cybersecurity plan.