Seattle–Tacoma International Airport is the primary international airport serving Seattle and its surrounding metropolitan area in the U.S. state of Washington. It is in the city of SeaTac, which was named after the airport's nickname Sea–Tac, approximately south of downtown Seattle and north-northeast of downtown Tacoma. The airport is the busiest in the Pacific Northwest region of North America and is owned by the Port of Seattle.
The entire airport covers an area of and has three parallel runways. FAA data effective April 17, 2025. It is the primary hub for Alaska Airlines, whose headquarters are near the airport. The airport is also a hub and international gateway for Delta Air Lines, which has expanded at the airport since 2011. , 37 airlines operate at Sea–Tac, serving 96 domestic and 37 international destinations in North America, Oceania, Europe, the Middle East, and Asia.
Sea–Tac was developed in the 1940s to replace Boeing Field, which had been converted to military use during World War II. A site near Bow Lake was chosen in 1942 and construction began the following year with funding from the federal government, Port of Seattle, and the City of Tacoma. The airport opened on October 31, 1944. The first scheduled commercial flights from the airport began in September 1947 and the terminal was dedicated on July 9, 1949. Sea–Tac was expanded in 1961 to accommodate jetliners and added new concourses and satellite terminals by 1973. The main runway was extended several times and twinned in 1970; the third runway opened in 2008 following several decades of planning due to local opposition.
Several major concourse expansions and renovations were initiated in the 2010s to accommodate passenger growth at Sea–Tac, which had become a new hub for Delta Air Lines. A new international arrivals facility opened in 2022 as part of the program. In 2023, Sea–Tac served 50,887,260 passengers, 2% below its previous record set in 2019.
By 2025, Seattle–Tacoma International Airport set an all-time record with 52,715,181 passengers served.
History
Construction and early growth (1942–1967)
A shared public airport was proposed by the Port of Seattle and Port of Tacoma in the late 1920s, but deferred plans after the legality of public ports operating such facilities was rejected by the state attorney general in a published opinion. The state legislature authorized municipal corporations such as public ports to establish aviation facilities in 1941. The Port of Seattle accepted a $1 million grant (equivalent to $ in dollars) from the Civil Aeronautics Administration in March 1942 to construct a new airport to serve the Seattle area after the U.S. military took control of Boeing Field during World War II. A site on U.S. Route 99 near Bow Lake south of Seattle was chosen at the end of the month ahead of another candidate near Lake Sammamish that was considered too close to the Cascade Range. The City of Tacoma provided $100,000 towards the airport's construction costs as part of a deal for the Bow Lake site, centered around an existing private airfield plagued by heavy fog. Construction of the airport, which was named Seattle–Tacoma in recognition of Tacoma's contribution, began with a groundbreaking ceremony on January 2, 1943.
The project was originally estimated to cost $1.7 million (equivalent to $ in dollars), but the sandy soil conditions drove the final construction price to over $4.2 million (equivalent to $ in dollars). The airport's plateau was formed through of excavated earth. A proposal to rename the airport for Boeing president Philip G. Johnson shortly after his death in September 1944 was rejected by Port of Seattle commissioners due to the objections of Tacoma. The first ceremonial landing at Seattle–Tacoma Airport was made on October 31, 1944, by a United Air Lines DC-3 carrying local elected officials and civic leaders. The first commercial flights launched in May 1945 with Northwest Airlines, but use was limited due to the U.S. Army Air Force's need for the airport to stage Boeing B-29 bombers for delivery. Various airlines had irregular flights to the airport, which used a Quonset hut with limited heating as a terminal until a permanent building was financed by a bond issue that voters approved in 1946.
The first scheduled commercial flights began on September 1, 1947, with Northwest Airlines and Western Airlines operating ten daily departures. They were joined by United, Alaska, Trans-Canada, Western, and Pan Am by 1951 as airlines departed from Boeing Field. The terminal at the renamed Seattle–Tacoma International Airport was formally dedicated by Governor Arthur Langlie on July 9, 1949, in front of a crowd of 30,000 spectators. The building, designed by architect Herman A. Moldenhour, included a rooftop control tower and glass curtain walls in the concourses. The airport originally had four runways at 45-degree angles, between long, for crosswind operations. The two perpendicular runways were arranged into an "X"-shape that intersected near the longest, north–south runway; an additional runway to the south ran east–west. The terminal building's "inverted V" shape was arranged to match the runway layout. The north–south runway (now Runway 16L/34R) was lengthened to in 1950 at a cost of $900,000, to in 1955, and to in 1958 to support commercial jetliners.
The enlargement of the airport's runways was precipitated by the major augmentation of commercial air traffic in the 1950s. Larger aircraft such as the Douglas DC-6, which introduced a pressurized cabin; the DC-7; Lockheed Constellations; and Boeing 377 Stratocruisers were some of the last turboprops to fly long-distance from Seattle. By 1957, Sea-Tac hosted 400 flights per week, with United as the largest carrier, offering 260 of those. The Boeing 367-80 or Dash-80, the first aircraft to demonstrate the potential of jet aviation, was accommodated by the 1955 runway extension when it first flew into Sea-Tac on September 27, 1956. The first regular jet service to Sea-Tac was provided by Pan Am on October 3, 1959, when a Boeing 707 departed for Honolulu. In 1961 Alaska introduced Convair 880 service on its lucrative Anchorage–Seattle flights after Northwest and Pan Am had introduced the type on the same route, which reduced flying time to three hours from the eight-hour, multi-stop journey on piston-engined planes. Braniff and United introduced an interchange service between Houston and Seattle on DC-6s, where the airline crews switched on the stopover in Denver; by 1965 the DC-6s had been replaced by Boeing 720s. United, meanwhile became the first carrier to serve Sea-Tac with Douglas DC-8s when it introduced them on the routes to Chicago and Idlewild (now JFK) Airport in New York. By 1962 Northwest offered flights from Sea-Tac to six destinations, including Portland, Honolulu, Anchorage, Spokane, and Chicago, while Pan Am served Fairbanks, Honolulu and offered transatlantic service to London. Western Airlines introduced 720 service from Sea-Tac on routes to Portland, Minneapolis-St. Paul, Los Angeles, and San Francisco after acquiring Pacific Northern Airways in 1967. Jet service on 707s and its sister 720s was augmented with the addition of the three-engine Boeing 727 in the mid-1960s, which allowed passenger numbers to double at Sea-Tac during that decade. Alaska introduced these on service to Anchorage and Sitka in 1966, while Braniff International had service on the 727 to both San Antonio and Dallas in 1967, and Western introduced it on service to Seattle in 1970.
The first parking lot at Sea–Tac opened in 1955 with room for 527 vehicles. The United States Postal Service opened its air mail terminal at the airport in 1957 to serve areas west of the Mississippi River and mail bound for Asia; other government agencies, including the Weather Bureau and the Customs Service also established offices at Sea–Tac. On June 28, 1959, Japan Airlines became the first international carrier from Asia to operate at Sea–Tac when it began its service to Tokyo. Several projects were completed by 1961 to prepare for the Seattle World's Fair the following year, including a runway extension over South 188th Street, which was placed in an automobile tunnel that opened in July 1961. During construction of the runway extension in February 1961, the fossilized skeleton of a Megalonyx jeffersonii giant sloth was discovered and excavated for display at the Burke Museum in Seattle. The two-story North Concourse (later named Concourse D) opened a month later with four gate positions to prepare for regular jetliner service; the concourse's wing was long and wide. The South Concourse (now Concourse A) opened in May 1961 alongside an expanded parking lot with capacity for 2,000 vehicles.
The long Concourse B opened in December 1964. It added eight gate positions, bringing the total to 19, a area housing international arrivals and the offices of U.S. Customs, Immigration, Public Health and the Department of Agriculture. Concourse C opened in July 1966. Four years later, it was extended to include another 10 gates, bringing the total to 35. The first non-stop flights from Sea–Tac to mainland Europe began in September 1966 with Scandinavian Airlines, who used a polar route to reach Copenhagen. A parallel second runway was completed west of the main runway in 1970.
Later expansions and third runway (1967–2008)
The Port embarked on a major expansion plan, designed by The Richardson Associates and lasting from 1967 to 1973, adding a second runway, a parking garage, two satellite terminals and other improvements. In 1973, $28 million new terminal was built over and around the 1949 structure; the new terminal quadrupled the area for public use. On July 1, 1973, the airport opened two new satellite terminals, along with an underground train system to connect them to the Main Terminal. These fully automatic shuttle trains were among the first of their kind in the United States. Also unprecedented in any U.S. airport: as part of the expansion the Port commissioned $300,000 worth of artworks; these were the start of what would become a large public art collection owned by the Port.
In the mid-1980s, the Main Terminal was renovated and another was added to the north end. Concourse D was expanded in 1987 with a rotunda that added four new gates. In 1993, Concourses B, C, and D were renovated. The project, designed by NBBJ, included the addition of and the renovation of of space in Concourses B, C, and D. On June 15, 2004, the new Concourse A was unveiled with 14 new gates, a dozen new restaurants, new artwork and the airport's first moving sidewalks.
Residents of the surrounding area filed lawsuits against the Port in the early 1970s, complaining of noise, vibration, smoke, and other problems. The Port and the government of King County adopted the Sea–Tac Communities Plan in 1976 to address problems and guide future development. The Port spent more than $100 million over the next decade to buy homes and school buildings in the vicinity, and soundproof others nearby. In the mid-1980s, the airport participated in the airport noise-compatibility program initiated by Congress in 1979. Airport-noise contours were developed, real estate was purchased and some homes were retrofitted to achieve noise mitigation.C. Michael Hogan, Ballard George et al., Residential noise insulation at Seattle Tacoma International Airport, Earth Metrics Inc., published by the Federal Aviation Administration and Seattle Tacoma International Airport (1984).
In 1978 the U.S. ended airline regulation, and the U.S. airlines were allowed to determine routes and fares without government approval. Deregulation resulted in some new service to Seattle, including from TWA, then the fourth-largest U.S. airline, as well as Delta, National, and American.