Question: US Aiways Shuttle services an airport that is a fortress hub for who?

Context paragraphs:
Rockaway Park Shuttle: The Rockaway Park Shuttle is a shuttle service of the New York City Subway operating in Queens.  It connects with the A train at Broad Channel station and is the latest iteration of the Rockaway Shuttle services that have been running in the Rockaway peninsula since 1956.  This shuttle train provides service to the western part of the peninsula, with a terminus at Rockaway Park–Beach 116th Street.  The fully aboveground route operates on trackage that was originally part of the Long Island Rail Road's Far Rockaway Branch until the mid-1950s.

Altoona Metro Transit: Altoona Metro Transit (AMTRAN) is a public transportation service located in Blair County, Pennsylvania.  It provides bus and paratransit service to Altoona, Holidaysburg, and select communities in the region.  Several high school bus services are subsidized by the service, as well as shuttle services for Penn State Altoona.

US Airways Shuttle: US Airways Shuttle was the brand name for US Airways' hourly air shuttle service operating in the Northeastern United States.  It served Logan International Airport in Boston, LaGuardia Airport in New York City, and Ronald Reagan Washington National Airport in Washington, D.C.

Citylink Coach Services: Citylink Coach Services Inc. is an intercity bus company in the Philippines operated under First Oceanic Property Management Inc., an affiliate company of Megaworld Corporation.  It plies routes from Eastwood City, in Libis, Quezon City to Newport City, in Villamor Air Base, Pasay via C-5 Road, making the first bus company to traverse along the said road.  This company offers shuttle services only for those who are working to the companies operated under Megaworld Corporation.

Golden Bay Air: Golden Bay Air Limited is a small airline based in Takaka, New Zealand.  The airline currently operates three light aircraft from Takaka to Wellington and Karamea, and also from Nelson to Takaka and Karamea with connecting road shuttle services to the Abel Tasman National Park, the Heaphy Track in the Kahurangi National Park and to and from Takaka township.  Other services provided by the airline include charter flights around New Zealand flown on demand and preset scenic routes around the National Parks as well as Farewell Spit.  Golden Bay Air originated in 2006 as Capital Air and later changed its name in 2009.

Citilink: Citilink is a low-cost airline headquartered in Jakarta, Indonesia.  It was established in 2001 as a low-cost subsidiary of Garuda Indonesia, set up to operate shuttle services between Indonesian cities.  Since July 30, 2012 Citilink has officially operated as a separate business entity from Garuda Indonesia, operating 14 aircraft with a new callsign, logo and uniform.  Its main hub is Juanda International Airport, Surabaya, East Java.  The airline was banned from operating in EU airspace until June 16, 2016.  Since then, Citilink is allowed to fly into EU airspace.

Prussian T 18: The Prussian Class T 18s were the last tank locomotives developed for the Prussian state railways.  They were originally intended for services on the island of Rügen as replacements for Class T 12 and T 10 engines.  They emerged when a class of locomotive was conceived in 1912 that was to handle express and passenger trains in border areas or in shuttle services on short routes.  A tank engine design with symmetrical running gear was envisaged because, unlike a tender locomotive, it could run equally fast forwards and backwards and could be operated on return journeys without having to be turned on a turntable.  Its power and top speed were to be the same as those of the P 8.  Robert Garbe designed this 4-6-4 (2'C2') tank locomotive for 100 km/h with a 17-ton axle load and contracted the "Vulkan Werke" in Stettin to build it.  It was given the designation T 18.

Ronald Reagan Washington National Airport: Ronald Reagan Washington National Airport (IATA: DCA, ICAO: KDCA, FAA LID: DCA) is an international airport 3 mi south of downtown Washington, D.C. in Arlington County, Virginia, United States.  It is the nearest commercial airport to the capital and serves the Baltimore-Washington metropolitan area.  For decades it was called Washington National Airport before being renamed to honor President Ronald Reagan in 1998.  The Metropolitan Washington Airports Authority (MWAA) operates the airport with close oversight by the federal government due to its proximity to the national capital.  It is a fortress hub for American Airlines.

Butetown branch line: The Butetown branch line, also known as the Cardiff Bay Line, is a commuter railway line in Cardiff, Wales from Cardiff Bay and Cardiff Queen Street.  The service pattern used to comprise a mixture of shuttle services along the branch and through trains along the Rhymney Line to Caerphilly, or the Coryton Line to Coryton, but since December 2005 is a shuttle service from Queen Street station.

Air shuttle: An air shuttle is a scheduled airline service on short routes with a simplified fare and class structure.  No exact definition exists, but frequency is usually hourly or more often and travel time is typically an hour or less.  Network airlines may operate shuttle services as one-class or no-frill services, similar to low-cost airlines.

Supporting paragraphs: US Airways Shuttle Ronald Reagan Washington National Airport
Answer: American Airlines