Two military fighter jets escorted two small planes from an area over Hanford on Thursday morning during a drill, startling Hanford workers.

Vivian Wilson, a community manager from the North American Aerospace Defense Command Western Air Defense Sector, said two planes were intercepted at 11:30 a.m. by two F-15 fighter jets scrambled from the Portland Air National Guard Base.

Some Hanford workers spotted only one plane being intercepted, though two Cessna 182s were involved in the drill, Wilson said.

One witness, who asked not to be identified, described seeing one of the Cessnas.

"The small plane was circling over Hanford for quite a while, then all of a sudden these two (jets) show up and start circling the small plane," they said. "At one point, it looked like one of the fighters came real close to the plane, like it was trying to get its attention."

Eventually the jets herded the plane out of the no-fly zone heading north, then returned a short time later and continued to circle the Hanford reservation, the witness said.

Wilson said the drill was part of a two-pronged exercise "of a 9/11 nature," testing forces' ability to respond to simultaneous threats. While theF-15s were responding to Hanford, a pair of F-16s were scrambled from Ellington Field in Texas to respond to another simulated threat involving an unknown aircraft making a border crossing into the U.S. from Mexico.

Wilson said the exercises are planned to avoid any local disruption. The last such exercise over Hanford was July 17.

"Hanford is a natural selection for an exercise because it is high priority infrastructure," Wilson said. The Department of Energy was not notified of the drill.

Pilots generally are aware they will be tested by such drills but are not made aware when they will occur.

"The overall purpose is to test our readiness," Wilson said.

The drills are conducted regularly within the agency's western region, which extends from the Pacific Coast to the Mississippi River, covering73 percent of the continental United States. The sector headquarters is at McChord Air Force Base near Tacoma.

"Our commander is very aggressive in exercise scenarios," Wilson said. "The exercises are not at all rare."