It’s time for exotic birds to alight in Oshkosh : About 800,000 people, many in unique aircraft, flock here for the Experimental Aircraft Assn.’s annual fly-in.

Slim Caselman says he is one of the early birds.

Actually, he flew here earlier than anyone else in his “bird,” a 1958 Clark 12, so that he could secure his favorite spot for the annual Experimental Aircraft Assn. fly-in convention.

Caselman and his wife, Holly, arrived from Meadville, Mo., nearly a month before the weeklong event that started today. As he has done for 12 years, Caselman parked his plane in a field next to Wittman Regional Airport, pitched a tent and set up a canopy over an area that serves as the couple’s outdoor living room and kitchen.

“I have a clear view of all the air shows,” said Caselman, sitting in a reclining chair that faces a runway. “They have the world’s best in aviation here--the best welders, the best fabric people and the best aerial acrobats. You can gain any amount of knowledge you want from the experts in the field.”

The Caselmans are among about 40,000 aviation enthusiasts who camp out each year in fields near the complex that houses the EAA headquarters and the Air Adventure Museum. But they represent only a fraction of the estimated 800,000 people who converge on this city of 55,000 residents to watch the air shows, compete for awards and view exhibits and workshops on building and restoring aircraft.

Because of the large crowds, traffic control is a problem--on and off the ground. The EAA uses volunteers such as Caselman to help steer drivers and pilots in and out of parking areas. About 60 Federal Aviation Administration air traffic controllers work to direct the 12,000 or more planes that are flown to the convention.

The large crowds also boost the local economy. Thirty food stands and three grocery stores are on the 1,400-acre convention site. More than 1,200 people are hired as temporary employees. And since area hotels get booked in advance, residents who want to rent out their homes, portions of their homes or apartments can register with a referral service offered by the city Convention & Visitors Bureau.

One woman who was registering her house this year said her family stayed in the basement two years ago while the rest of the house was rented. “Last year we put up a tent in the back yard and stayed there,” she said.

When Paul H. Poberezny founded the EAA in 1953 with the help of a few friends, he never realized that the association would expand to include more than 140,000 members in 750 chapters worldwide. It even has members who have been out of this world: All the astronauts on the recent shuttle Atlantis mission belong to the EAA.

“I didn’t realize then that people all over the world had the same interest,” Poberezny said. “It grew way beyond what I ever envisioned. So many people have said it has been the savior of general aviation in this country.”

The EAA headquarters started out in the basement of Poberezny’s home in Hales Corners, Wis., near Milwaukee. He was elected as the group’s first president, a position he held for 37 years until his son, Tom, was selected for the post in 1989.

The first fly-in was at a Milwaukee airfield in September, 1953. It drew about 40 people. The event was later moved to Rockford, Ill., and then to Oshkosh in 1970.

“We outgrew Rockford,” Paul Poberezny said. “Steve Wittman had designed the Oshkosh airport so it was like two airports in one, with two runways that didn’t cross each other. That made it safer for fly-in events.”

The Oshkosh airport is named for Wittman, who gained international recognition as an air racing pilot and a designer of home-built planes. He was killed in April at age 91 when the plane he was flying crashed in northeastern Alabama. He will be honored at this year’s fly-in with groundbreaking ceremonies for a replica of his hangar.

Another pilot noted for his accomplishments in air speed will be honored this year. Chuck Yeager, a combat veteran and test pilot who was the first person to fly faster than the speed of sound, will receive the Freedom of Flight Award. Previous winners include astronauts Neil Armstrong and Robert L. (Hoot) Gibson, entertainer John Denver, actor Cliff Robertson and hotelier Barron Hilton.

Gibson was commander of the Atlantis when it docked with the Mir space station earlier this month. He will be at the fly-in to talk about that mission.

Other activities this year include a salute to the era of air racing and a 50th-anniversary commemoration of the end of World War II.

Although planes such as the antiques and classics, home-builts and ultra-lights are a highlight of the fly-in, Slim Caselman believes that people are the real attraction.

“This is like a big family reunion,” said Caselman, who makes his own ice cream for people who stop to visit. “Every year our Oshkosh family grows. We keep a guest list so we can send out Christmas cards.”