With Sea-Tac fast approaching its maximum capacity, now is the time for the state and the Puget Sound region to begin discussing where to add more passenger-airport capacity.

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Sea-Tac International Airport is the fastest-growing major airport in the country, leaping ahead of its growth forecasts. It’s projected to reach maximum capacity in 2034 — or sooner if its recent, torrid growth continues.

Last year, the number of passengers boarding and disembarking airplanes grew 7.7 percent to 37.5 million, a rate more than double the national average. Just through this July, it’s up another 13.5 percent.

Adding airport capacity — and making sure we don’t get stuck waiting on the tarmac like we are on the freeway — is not a far-off problem. Regional leaders may take a decade or more to reach a consensus on where and how to add additional capacity. Navigating inevitable legal challenges and building that capacity might add another decade to the schedule.

If we start the conversation now, additional airport capacity might be ready around the time Sea-Tac is completely maxed out.

Remember, the region took 20 years to deliberate and build Sea-Tac’s third runway after it became apparent that additional capacity was needed.

Now, seven years after that project was completed, the airport’s operator is in building mode. The Port of Seattle this year is beginning $1.9 billion worth of upgrades and capacity improvements.

Topping that list are a new international-arrivals facility that will cost more than $600 million and a $521 million expansion of the north concourse, adding eight new gates.

A fully functioning airport system is essential to the continued success of Washington’s trade-dependent economy.”

Also planned is the replacement of Sea-Tac’s center runway and construction of a new, high-speed baggage-handling system expected to cost $321 million.

The Port will also be looking to expand to the north and south, potentially relocating maintenance hangars and cargo warehouses to accommodate its growth.

Even with all this remodeling, Sea-Tac could reach capacity in as little as six to 10 years at current growth rates, Port of Seattle Chief Executive Ted Fick recently told The Times editorial board. The current pace is likely to ease up soon. But demand for more airport capacity will continue to rise, especially with Delta Air Lines using Sea-Tac for an international hub.

Boeing Field in Seattle’s midsection is not an option for a major expansion because its runway alignment with Sea-Tac creates air-traffic conflicts. That leaves Paine Field in Everett as the most likely candidate.

“There will be a point in time where that’s probably the next phase,” Fick acknowledged.

Paine Field was built in the 1930s to be a regional transportation hub. It was used by the military before it became an industrial center in the 1960s.

Neighboring communities allowed to develop around Paine Field bitterly oppose passenger service there, although the Federal Aviation Administration decided in 2012 that service wouldn’t cause significant harm.

The potential will be tested by a contract the Snohomish County Council approved in March. A New York company, Propeller Airports, could build and operate a small terminal for up to 23 passenger flights per day. Propeller is still lining up financing and airline customers.

The project also faces legal challenges by an opposition group and the cities of Mukilteo and Edmonds, offering a preview of the hurdles the region will face when Sea-Tac is full.

Almost nobody wants a nearby airport to expand — remember the battles over the third runway? But Sea-Tac has finite space and more people are moving, visiting and doing business in the area.

Snohomish County alone is expected to grow by 200,000 people over the next two decades. Consider how many of those people will travel on Interstate 5 to and from Sea-Tac.

The Sound Transit 3 wishlist includes a light-rail extension to Paine Field. That’s a smart move, not just to reach Boeing and other employers but also to prepare for potential airport expansion. It could create options similar to what travelers have in the Bay Area, which has rail connections to the Oakland and San Francisco airports.

The Port of Seattle and the FAA should also address the region’s long-range needs for airport capacity when they revise Sea-Tac’s airport master plan over the next year. The new plan is likely to call for a new terminal and up to 45 new gates, but it should look at additional growth options, including passenger service at other airports in the region.

Gov. Jay Inslee, the Legislature and the state Department of Transportation should also move major-airport expansion planning off the back burner. A starting point could be to refresh the Long-Term Air Transportation Study done for then-Gov. Chris Gregoire in 2009. It warned of the coming capacity crunch, but was overshadowed by the recession.

The still-relevant study said the state’s airport system is threatened by land-use encroachment, limited resources and “a lack of clarity as to the state’s role in helping it survive.”

It also said the region has a critical need for long-range planning and bold leadership to support future airport demand.

A fully functioning airport system is essential to the continued success of Washington’s trade-dependent economy. Let’s start discussing how and where to add capacity before it’s a crisis so we can do this job right.