A massive aerial search-and-rescue effort in Southwest Alaska is continuing after a float plane and four men on board were reported missing Saturday. The three passengers work for Katmai National Park, and family members as well as National Park Sservice officials remain optimistic.

Search crews were delayed leaving King Salmon Monday morning, but the weather over the search site has since cleared up. Five agencies are working together, using 10 aircraft in a full-scale search to locate the plane, the pilot and passengers.

The DeHavilland Beaver left Swikshak Bay Saturday at about 2:45 p.m., heading to King Salmon. The flight usually takes less than an hour, but the plane never arrived.

“The expected trip would've taken them north out of Swikshak around Cape Douglas to the McNeil River, Kamachak Bay area, and then up one of those river drainages to the interior of the park -- sort of connecting through Kulik Lake and then out that way to King Salmon,” said NPS spokesperson John Quinley.

The U.S. Coast Guard, the Alaska Air National Guard, Alaska State Troopers and a few private air companies based in King Salmon searched for the missing plane near the coastline and inland on Sunday.

As weather cleared Monday, crews resumed the search further inland after reports that the Beaver’s pilot indicated he was taking a different route due to bad weather.

“The weather today is excellent for the search -- we've got clear skies and excellent visibility,” Quinley said.

The missing Park Service employees are 26-year-old Mason McLeod and two brothers, 28-year-old Neal Spradlin and 20-year-old Seth Spradlin. The pilot is Branch River Air Services employee Marco Alletto, 47, of King Salmon.

The Spradlin brothers are originally from Indiana. But Neal, the oldest, has lived in Alaska for the past seven years, and has worked full-time at Katmai National Park five years in the summer while residing in Girdwood in the winter. His younger brother Seth was working his second summer at the park as a seasonal employee.

Family members in Indiana say they are praying for good news.

“Right now, we're just holding fast to our belief that they're sitting in a cove, that they're holed up and waiting for the weather to clear or that a plane will spot them and they'll be able to get out ,” said the Spradlins’ brother-in-law, Daniel Rowe.

Park Service officials in Alaska, however, are concerned because there have been no radio transmissions from the missing plane.

“So, certainly a high level of concern, and we really want to locate them today,” Quinley said. “Because with as bad of weather as we've been having over the summer, with a day like this you want to get it done.”

The Spradlin family aren’t the only ones remaining optimistic as search efforts continue, with reports that the Beaver was carrying extensive supplies.

“We're hopeful this will have a good outcome,” Quinley said.

Most aircraft involved in the search are equipped with GPS tracking devices, which allow the search to be better managed.

On Monday, helicopters searched the coast of Katmai from Katmai Bay to Swikshak Bay on the chance the missing aircraft began an unexpected route back to King Salmon on Saturday afternoon -- but no sign of the missing plane was found.

Contact Lori Tipton at ltipton@ktuu.com