Marvin Tyacke usually ignores the planes that fly over his Post Falls home.

Knowing he resides under the east-west flight path for several airlines, he said the planes overhead rarely attract his attention.

But sitting in his yard on Monday, he saw something different.

"I looked up and saw the contrail of a big airliner going east, and as I watched, it started making a big right turn. I thought to myself, 'Oh, he must not have remembered he had to go to Boise,'" the 81-year-old said with a chuckle.

Instead, the plane continued to turn in a circle, which it traced again and again.

Then Tyacke spotted a small chaser plane just outside the larger aircraft's window.

"I was just wondering, 'Something must be going on up there,'" he said. "'Is there a hijacking going on, or what?'"

Nothing quite so dire.

The large plane that several folks have reported seeing around Kootenai County this month, sometimes at low altitudes, sometimes accompanied by a chaser plane, is actually the newest Boeing 747-8 freight plane running flight tests.

One of only three such planes running tests in the nation, it's flying regularly out of the Grant International Airport in Moses Lake, Wash., usually sticking to the skies of eastern Washington.

Occasionally, it makes its way into North Idaho, said company spokesman Tim Bader.

"These are validating the performance characteristics of the airplane," Bader said.

The flight tests have been running since the plane arrived in Moses Lake in late February, he said.

On Monday, the plane was flutter testing, Bader added, or examining how the airplane dampens vibrations at certain speeds and altitudes.

The accompanying chaser plane was filming the freight plane, he said.

"It's watching to see how the airplane's acting in the air to make sure it's acting appropriately," he said.

He assured there were no risks for folks walking below.

"This airplane's completed its initial airworthiness already," he said.

Where the flight tests occur depends on weather, Bader said.

Generally, the plane heads wherever the sky is clearest.

"It certainly varies day to day," he said. "As they start going deeper into testing, they'll start going where certain conditions are, like locations where there are cross winds and where it's really hot."

Past flight test routes can be viewed by going to flightaware.com and typing "BOE501" into the flight tracker window.

The 747-8 freighter is the largest plane Boeing has ever built, Bader said, 18 feet longer and 13 feet wider than other 747s in the air.

The other two test planes are flying out of Palmdale, Calif., and Seattle, Bader said.

The company is working toward first product delivery in late 2010, he said. Before then, all test planes will be relocated to southern California.

"That (Moses Lake) airplane will probably be there for a little while more in this quarter," Bader said.