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. 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. 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 first parking lot at Sea–Tac opened in 1955 with room for 527 vehicles. 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) 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. 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. 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. 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. 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. and
United planes at the North Satellite Terminal in 2008 Shortly after the death of U.S. Senator
Henry Martin "Scoop" Jackson, the Port Commission voted on September 13, 1983, to change the airport's name to the Henry M. Jackson International Airport. Citizens of Tacoma were angered by the removal of their city's name despite their contribution to the airport's original construction budget, which had come with a promise to share the name. An additional complicating factor was the existence of another Jackson International Airport (now
Jackson–Medgar Wiley Evers International Airport) in
Jackson, Mississippi. During the November 1983 elections, an advisory referendum in Tacoma on the airport's name endorsed the original name by a 4–1 margin and two incumbent Port commissioners were defeated by candidates in favor of restoring the Sea–Tac name. Helen Jackson, the widow of the late senator, expressed her desire that their family remain neutral in the debate. With a 3–2 vote of the Port Commission on February 28, 1984, the name reverted to Seattle–Tacoma International Airport and the four signs with Jackson's name were removed. In the late 1980s, the Port of Seattle and a council representing local county governments considered the future of air traffic in the region and predicted that the airport could reach capacity by 2000. The rising use of regional airliners such as
Horizon Air caused aircraft movements to triple from 1978 to 1990 and air cargo use at the airport had also risen dramatically. In 1992, the planning committee concluded that the best solution was to add a third runway to the airport and construct a supplemental two-runway airport in one of the neighboring counties. Members of the community opposed a third runway, as did the
Highline School District and the cities of
Des Moines,
Burien,
Federal Way,
Tukwila, and
Normandy Park, but a 1994 study concluded there were no feasible sites for an additional airport. The Port of Seattle approved a plan for the new runway in 1996, prompting a lawsuit from opponents. The Port secured the necessary permits by agreeing to noise reduction programs and environmental protections. Runway opponents appealed these permits, but dropped their challenges in 2004. The third runway, measuring long, opened on November 20, 2008, with a construction cost of $1.1 billion. Parallel to the existing two, the new runway is west of runway 34R, allowing landings on both in times of low visibility. The older runways are apart, too close to allow use of both in low visibility. The third runway project included of fill dirt and several retaining walls, the longest of which is long and tall.
Modernization and expansion (2008–present) The airport's Central Terminal building was renovated and expanded in 2003 in a project designed by
Curtis W. Fentress, of
Fentress Architects. The renovation and expansion began in 1996 and underwent extensive modifications to accommodate new security requirements following the
September 11 attacks in 2001. In 2014,
Delta Air Lines announced plans to expand Seattle into a transpacific hub. Since then, Delta has added numerous international flights and dozens of domestic flights to feed those services. Delta's increased presence in Seattle has been seen by some industry analysts as a response to
United Airlines' transpacific hub at
San Francisco, as well as Delta's disenchantment with its former Tokyo–Narita hub. In late 2021, shortly after Alaska Airlines joined American Airlines in the
Oneworld alliance, American announced that they would increase their international presence in Seattle. However, as of 2023, American had abandoned plans for long-haul flights to Asia from Seattle (including its proposed service to
Bangalore, India) and ended service to London-Heathrow, their only intercontinental service from Seattle. The North Satellite Terminal only received limited upgrades since it opened in 1973, and needed modernization. The Port of Seattle initially looked at simply updating the terminal in a project it called the North Satellite Renovation Plan (NorthSTAR). In 2016, the Port announced it would also significantly expand the terminal. The $550 million project called the North Satellite Modernization increased the size of the North Satellite by The project was initially expected to be completed by 2021 at a cost of $766 million, though revised to $968 million in late 2018. The old customs and immigration facility was located in the basement of the South Satellite, and operated well over its design capacity. Additionally, the process for passengers was complicated by the satellite's isolated location. With the opening of the new IAF, Concourse A will now also be used for arriving international flights, nearly doubling the number of gates capable of serving arriving international passengers. The South Satellite Terminal is also planned to be renovated. The airport's digital infrastructure, including its website, phone lines, check-in system, and automated baggage sorting, was disabled by a cyberattack on August 24, 2024. Most of the systems were restored by August 31, but the Port of Seattle websites and passenger information systems remained offline.
Future The airport has seen record growth in passenger traffic in the 2010s and 2020s. The busiest day for outbound passengers was July 24, 2023, with 73,651 passengers; more than 198,000 passengers (departing, arriving, and connecting) passed through the airport that day. The previous record for outbound passengers was set on August 16, 2019, at 72,154. The growth has been partly fueled by the nationwide expansion of Seattle-based Alaska Airlines and by Delta Air Lines setting up a major international hub at SEA Airport. That growth has strained the airport's facilities and led the port to invest more than $2 billion into several expansion and renovation projects. The airport has six outbound
baggage handling systems with limited to no cross-connectivity. The system now in place is aging and reaching its maximum capacity. A $320.4 million project will create one unified, high-speed baggage system under the airport. That will allow bags to be checked from any ticketing counter, to receive security screening faster, and to be routed to any gate in the airport. The extra efficiency and speed will allow the airport to handle more baggage in the future without expanding the footprint of the baggage handling systems. The initial phase of the project was finished in 2018 and the entire system is scheduled to be completed in 2027. With estimates that the
Puget Sound region will grow by another one million people by 2035, the
Port of Seattle began developing the Sustainable Airport Master Plan (SAMP) in 2018 to meet
passenger and
cargo demands. The SAMP recommends more than 30 projects to improve efficiency and airport access, including a new terminal with 19 gates and an
automated people mover through three separate stations. Near-term projects that are scheduled to be completed in the 2020s include restroom renovations, security checkpoint expansion, and roadway realignment. A four-story addition to the existing structure of Concourse C began in 2023 and is scheduled to be completed in 2027 at a cost of $399 million; it includes a "central gathering place" under a large wooden ceiling. Further projects include an automated parking garage guidance system, a gateway project in cooperation with Alaska Airlines, Concourse A building expansion for lounges, improved curbside safety and accessibility, continued refurbishment of the Central Terminal, and a replacement of controls pertaining to the SEA Underground shuttles. ==Facilities==