The escalating battle between Alaska Airlines and Delta Air Lines at Seattle-Tacoma International airport has pushed passenger traffic at the Pacific Northwest airport to record levels.

In June, capacity at Seattle, measured in available seats, reached about 2.2 million, up 11.2% in one year and nearly 22.7% in five years, according to Innovata data.

Those gains propelled Seattle-Tacoma to the number 10 slot among the USA’s busiest airports, measured in available seats.

Seattle held the number 15 spot just five years ago, but has since leapfrogged Newark, Orlando, Miami and Houston, data shows.

Seattle top 10 USA airports

The growth has not gone unnoticed by the airport, which issued a media release on 16 July announcing that more than four million passengers had travelled through the airport in June, “breaking the four million passenger barrier for the first time”.

The capacity and passenger gains come as Seattle-based Alaska continues battling on its home turf with continuously-encroaching Delta, based in Atlanta.

Between them, those carriers have increased their number of flights from Seattle from about 9,000 in June 2013 to more than 12,100 flights this June, an increase of some 34%, Innovata shows.

Delta’s number of flights in that two-year period is up about 182%, while Alaska’s number of flight have increased 10.8%.

New routes launched from Seattle since June 2013

AK Seattle routes June 2015

New routes launched by Delta since June 2013

DL Seattle routes June 2015

The growth seems poised to continue.

In recent weeks, Delta has announced a host of new routes from Seattle, including those to Boston, Cancun, Missoula (Montana), Orlando, Pasco Tri-Cities and Victoria (British Colombia).

Other nonstop routes launched by Delta from Seattle in recent years include flights to Beijing, Hong Kong, London, Seoul Incheon and Shanghai Pudong.

Meanwhile, Alaska also continues to expand at Seattle.

This summer the carrier’s regional partner SkyWest Airlines launched flights from Seattle to Milwaukee and Oklahoma City.

Alaska has also announced plans to begin flights this fall from Seattle to Charleston (South Carolina), Nashville (Tennessee), New York JFK, Raleigh-Durham (North Carolina) and Charleston (South Carolina).

And, in the last several years, Alaska has expanded from Seattle to a number of east coast cities, including Detroit, Baltimore, Tampa and New Orleans. It has also added flights to Cancun, San Jose del Cabo and Puerto Vallarta in Mexico, Innovata data shows.

All that added capacity is beginning to pressure Alaska’s finances.

In May, the carrier announced that it expects “pressure on yields and load factors” in the second quarter of 2015.

Just days ago, the carrier predicted its capacity in available seat miles would increase 10.7% in the second quarter, and that unit revenues will decline about 5.5% in the period, to between 14.39 cents and 14.44 cents.

But those figures have not scared investors.

In a research update released 10 July, Wolfe Research raised its expectation for Alaska’s stock, noting that company passenger RASM in June will likely outperform average industry figures.

Source: Cirium Dashboard