Crews headed out for their fourth day of searching Tuesday for a small plane with four aboard that failed to return from a remote shore in Katmai National Park and Preserve.

There has been no sign of, and no signal from, the maroon de Havilland Beaver with white stripes (tail number N9313Z) since it left Swikshak Lagoon early Saturday afternoon with the pilot and three National Park Service maintenance workers. The three -- Mason McLeod, 26, and brothers Neal and Seth Spradlin -- had been tearing down the old Swikshak patrol cabin to make way for a new cabin.

On Monday crews flew over several river valleys along the northeastern coast of Katmai near Kamishak Bay. Search leaders thought the single-engine float plane, piloted by Marco Alletto, 47, of King Salmon, would have flown up one of the valleys, then along Kulik Lake west toward King Salmon

Ten aircraft – four helicopters and six fixed wing – participated in the search Monday. The multi-agency effort includes the National Park Service, U.S. Fish & Wildlife Service, Alaska State Troopers, U.S. Coast Guard, Alaska Air National Guard, Egli Air Haul, and Branch River Air. Other air taxi operators taking clients to the area have also informally joined the search. The National Park Service has a regional incident management team in place at the park’s King Salmon headquarters to assist the park coordinate the search.

Most aircraft involved in the search are equipped with GPS tracking devices, which allow the search managers to plot areas that were intensely searched during the first three days.

Today plans called for the search efforts to focus on areas that have been less intensively searched in the last three days.

Katmai is about 300 miles southwest of Anchorage.