WASHINGTON - The accident rate for drones was worse than all other types of aircraft during the past 20 years, though recently it has begun to improve, a Senate hearing was told Wednesday.

That safety record, which is approaching the crash rate of traditional aircraft, isn't reason to slow the coming boom in civilian uses for drones, Mary Cummings, director of Duke University's Humans and Autonomy Laboratory, told the Senate Commerce, Science and Transportation Committee.

Some military drones, such as the General Atomics Aeronautical Systems Inc. Predator, are now safer than privately operated planes, she said.

"As a former fighter pilot and a private pilot, I understand the importance of what I am saying — which is that a drone is, on average a better pilot than I am," she said.

Global sales of civilian and military drones may reach $89 billion during the next decade, according to a forecast by the Teal Group Corp., a Fairfax, Va.-based aerospace research company, and Congress has ordered the Federal Aviation Administration to craft rules for civilian operations by 2015.

Cummings didn't provide specific data about the rates of drone accidents on models other than the Predator.

The chief of the FAA, which on Dec. 30 granted approvals for six drone test and research sites across the nation, urged caution about introducing drones into the skies too quickly.

Because a drone's operator remains on the ground, aspects of unmanned craft are "inherently different" from traditional aircraft, FAA Administrator Michael Huerta said.

"Neither the technical nor operational capabilities necessary exist today to implement the opportunities described by visionaries, but their promises for 21st century conveniences are compelling," he said.

The hurdles for safe operation include developing technology that lets a drone fly and land safely if its radio link to the pilot is lost, he said. They must also be capable of detecting and avoiding nearby aircraft if they fly among other planes.

"History has made it clear that real risks accompany technological advances and their potential benefits," said Sen. Jay Rockefeller, D-W.Va., chairman of the committee. "Our job is to foster the growth and manage the risks."

The committee also heard a plea from a drone manufacturer that's getting swifter approvals in other countries than in the United States.

Japan's Yamaha Motor Co. has sold more than 2,600 RMAX remote-controlled helicopters for agricultural purposes, said Henio Arcangeli, vice president of planning for the firm's U.S. subsidiary.

"There is mounting commercial interest and need for the RMAX from farmers and growers in this country," Arcangeli said. Yamaha Motor Corp. U.S.A. is based in Cypress, Calif.

The helicopter, which weighs 140 pounds and is 9 feet long, has been used for 20 years in Japan and more recently in South Korea and Australia, he said. It is safer than manned crop dusters and uses less fuel and chemicals, he said.

While it's been tested in California, it isn't approved for U.S. commercial use, he said. He urged Congress to push the FAA to let it fly in unpopulated areas at low altitudes.