Shifting weather conditions -- from good to bad to good again -- have hampered search efforts for a plane missing for more than a week over Katmai National Park and Preserve.

While overcast weather Saturday limited aerial efforts to the afternoon hours, on Sunday the weather improved enough to allow flights to take off by 10:30 a.m. local time, according to National Park Service spokeswoman Adrienne Freeman.

If there was a benefit to Saturday's weather, though, it was that the conditions were very similar to those on August 21 when the single-engine float plane carrying three Park Service maintenance workers disappeared on a flight from Swikshak Lagoon to park headquarters at King Salmon, Ms. Freeman said Sunday during a telephone call from her office at King Salmon.

"Essentially the pilots who were out there yesterday were able to see things with the same eyes as the pilot would have," she said. "That’s a pretty critical information piece. It did help us decide where to look today.”

Since the hunt got under way for the maroon de Havilland Beaver with white stripes, more than 14,000 square miles of wildly diverse terrain have been searched. Despite the lack of a single bit of evidence as to what happened to the plane, Ms. Freeman said officials remained optimistic that its occupants -- Mason McLeod, brothers Neal and Seth Spradlin, and pilot Marco Alletto -- could have survived a crash and are waiting to be rescued.

"There’s a big level of survivability," she said, explaining that so many factors come into play in plane crashes.

The terrain, which in Katmai ranges from flat willow bottoms and swift rivers to vast expanses of heavy timber and glaciers, plays a tremendous role, as do the details that involve a crash. And then there's the wild card of fate. Back in July a single-engine plane crashed in Rocky Mountain National Park, and photos of the scene makes it difficult to believe the two occupants walked away with only minor injuries.

"For survivability, it’s not only the type of crash ... it’s also this terrain," Ms. Freeman said. "You have water, you have forestation, you have all this enormous range of terrain. That makes the survivability so hard to determine. How long could you survive if you landed at this elevation, with relatively warm temperatures? Probably a lot longer than if you landed on the side of a glacier. There are hugely varying factors in this. And because of the size of the search area, it’s going to be really difficult to determine" survivability.

Search officials had five helicopters and eight fixed-wing aircraft at their disposal Sunday. While maps depicting areas already searched would seem to indicate the entire 4.7-million-acre park has been closely examined, Ms. Freeman said those maps can be hard for the lay person to interpret.

When planes or helicopters fly over a particular search area, she explained, depending on the visibility and the terrain the spotter can only see about a half-mile on either side of the aircraft.

“What you do when you amplify the places in between those spots, you realize that there’s still a lot of world that’s not been reasonably searched from each of those flights,” said the spokeswoman.

While there have been news reports that questioned the judgment of the pilot of the missing plane, Ms. Freeman said the pilot and the company he flies for -- Branch River Air Service -- had been certified to work for the Interior Department.

Away from the active search, a regional Park Service investigator was heading to King Salmon on Sunday to begin work on the incident. Among the questions is why there were no communications between the pilot of the missing plane and the second one, which had departed Swikshak Lagoon 15 minutes later and safely returned to King Salmon. When he reached King Salmon the pilot of that plane reported that poor weather conditions forced him to fly much of the way 500 feet above ground level.

"There were no radio communications with them on the way home. None," she said. "That’s part of the investigation, because there were radio communications on the way out."

Also unknown is whether the second pilot took the same route back towards King Salmon as Mr. Alletto.

“There’s no designated route (between lagoon and King Salmon)," Ms. Freeman. "It’s a determination of local conditions. That’s the strength of having local people. They determine what’s best for their particular aircraft in their particular situation.”