(CNN) -- A private plane carrying four passengers that took off Sunday in western Montana is missing, said Mike Fergus of the Federal Aviation Administration.
Fergus said a concerned relative notified authorities the plane was overdue.
The aircraft was flying under visual flight rules and didn't file a flight plan, but the concerned relative said it took off Sunday from Missoula en route to Kalispell with a stop at Glacier National Park, Fergus said. No emergency signal has been sent from the aircraft, he said.
Two of the passengers were reporters for the Daily Inter Lake, a northwest Montana paper, but not on assignment, said Scott Crandell, assistant managing editor.
"We just want to find them OK," Crandell said
Sanders County Undersheriff Rube Wrightsman said the search is focused on Thompson Falls, a small city in his county in northwest Montana.