Boeing’s latest variant of the jumbo jet has been flying test runs in and out of Spokane International Airport this week.

The 777X, which is the largest two-engine passenger plane ever built, has been using Spokane as a testing site, Boeing spokesman Bernard Choi said. He would not say why Spokane was selected or how long test flights would continue here.

“The 777X is doing some flight testing and we thank the team (at Spokane International Airport) and Spokane community for their support,” Choi said in an email. “This is part of our rigorous test program for the 777X, which is progressing well.”

The latest version of the aircraft, which made its maiden flight Jan. 25 in Everett, includes both the 777-8 and slightly larger 777-9 models. Depending on how seats are configured, the planes can carry either slightly fewer or more than 400 passengers. The new 777X features composite wings are so long that 11 feet of the tips must be folded for the aircraft to fit in standard airport gates.

“It’s a beautiful airplane,” Spokane International Airport spokesman Todd Woodard said. “It’s an honor to be able to have that here.”

The new aircraft is powered by two GE9X engines, which at more than 15 feet across are the largest jet engines in the world. According to Boeing, the new 777-9 variant is the longest commercial aircraft ever built and 9 feet longer than the 777-300ER, which entered service in 2004.

“We’re conducting a comprehensive series of tests and conditions, on the ground and in the air, to demonstrate the safety and reliability of the design,” Choi wrote, “and have the flexibility to do so anywhere the requirements are met.”

Woodard said he’s not aware if Boeing sought special permission from the airport. He said the 777X came in just like any commercial aircraft.

“It’s quite large,” he said. However, Spokane International has runways large enough to handle any aircraft, he said.

“We are a diversion point for Asian airplanes, in particular, that may encounter fog” on the West Coast, he said. “We can fully accommodate any aircraft.”

According to Boeing literature, the company expects to deliver the first 777X in 2021. The program has won 340 orders and commitments from leading carriers around the world, including ANA of Japan, British Airways, Cathay Pacific Airways, Emirates Airlines, Etihad Airways, Lufthansa, Qatar Airways and Singapore Airlines.