FRANKFURT (Reuters) - German nudists will be able to start their holidays early by stripping off on the plane if they take up a new offer from an eastern German travel firm.

Travel agency OssiUrlaub.de said it would start taking bookings from Friday for a trial nudist day trip from the eastern German town of Erfurt to the popular Baltic Sea resort of Usedom, planned for July 5 and costing 499 euros ($735).

"It's expensive, I know," managing director Enrico Hess told Reuters by phone. "It's because the plane's very small. There's no real reason why a flight in which one flies naked should be more expensive than any other."

The 55 passengers will have to remain clothed until they board, and dress before disembarking, said Hess. The crew will remain clothed throughout the flight for safety reasons.

"I wish I could say we thought of it ourselves but the idea came from a customer," Hess told Reuters by phone. "It's an unusual gap in the market."

Naturism, or "free body culture" (FKK) as it is known in Germany, was banned by the Nazis but blossomed again after the Second World War, particularly in eastern Germany.

"There are FKK hotels where you can go into the restaurants and shops naked, for example," Hess said. "For FKK fans -- not that I'm one of them -- it's nothing unusual."

"I don't want people to get the wrong idea. It's not that we're starting a swinger club in mid-air or something like that," he added. "We're a perfectly normal holiday company."

(Reporting by Georgina Prodhan, editing by Paul Casciato)