The Federal Aviation Administration (FAA) (defendant) established regulations governing carry-on baggage and the operation of portable electronic devices (PEDs). The regulations generally required airlines to have an agency-approved carry-on baggage program, which controlled the size and amount of luggage that passengers could bring on a plane. Carry-on baggage was not defined in the regulation. Instead, airlines were instructed to describe what they considered carry-on baggage to be. The regulations also prohibited the use of most PEDs during flight, unless the airline had determined that the device would not cause interference with the aircraft’s navigation or communication system. Prior to 2012, the FAA recommended that most PEDs could be used during the main portion of the flight but not during takeoff or landing. The FAA then established an Aviation Rulemaking Committee to study and recommend changes to the agency’s PED policies. The committee made several recommendations designed to expand the use of PEDs, including during takeoff and landing, and it recommended an update to the policies for carry-on baggage to accommodate the use of PEDs. In response, the FAA issued new guidance documents. One of the new guidance documents was addressed to FAA safety inspectors and noted that the FAA did not need to approve an airline’s finding that expanded PED use would not interfere with flight safety. The notice stated that airlines would possibly need to consider updates to carry-on baggage policies and general concerns such as safely stowing large PEDs. The Association of Flight Attendants (AFA) (plaintiff) filed a petition for review of the guidance document in the United States Court of Appeals for the District of Columbia Circuit. The petition asserted that the guidance document was arbitrary and capricious in allowing small PEDs to be secured rather than stowed.