BOISE (AP) - A search underway in the central Idaho backcountry for five passengers who were in a small plane that disappeared Sunday is being complicated by heavy snow and low visibility.

About two dozen search and rescue personnel are combing a mountain ridge near the tiny town of Yellow Pine for a single-engine Beech Bonanza that lost radio and radar contact with controllers Sunday afternoon, said Lt. Dan Smith, of the Valley County Sheriff Department.

The plane carrying five family members was flying from Baker City, Ore., to Butte, Mont. The pilot reported engine troubles and asked controllers in Salt Lake City for coordinates to the Johnson Creek Airstrip, a grass-covered backcountry landing strip near the Frank Church-River of No Return Wilderness.

Smith said heavy snow that has been falling all day Monday and low clouds have twice grounded planes and Idaho Army Air National Guard helicopters brought in to help search by air. Crews began focusing on the ridge top just east of the landing strip based on cell phone signals, Smith said.

"We have no idea what the status of things is right now," he said. "They could have landed safely somewhere and just can't communicate."

Signals from the plane's built-in emergency locator transmitter, designed to go off in crashes, have not yet been detected, he said.

Authorities have not identified the pilot or the others on board.

The plane's registered owner is Dale Smith, of San Jose, Calif., according to Federal Aviation Administration records. Smith obtained his pilot's license in 2005 and had a second-class medical certification, allowing him to operate commercial aircraft.

A telephone message left by the Associated Press Monday at Smith's home was not immediately returned.