A Toyota Motor Corp. (TM) executive engineer described as the "American father of the Prius" and who was among the country's top experts on gas-electric hybrid vehicles died in a plane crash, officials said Sunday.

David Hermance, 59, was piloting an experimental plane when it went down Saturday afternoon about 50 yards off Los Angeles' San Pedro area.

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A search team found the wreckage of the two-passenger Interavia E-3 aircraft submerged in 60 feet of water Sunday morning, county Fire Capt. Mark Savage said.

"The plane was coming straight down, like it couldn't pull out of a steep dive, and it just hit the water," a witness, Rick Wadlow of Palos Verdes, told KABC-TV.

Hermance was executive engineer for Advanced Technology Vehicles at Toyota's technical center in the Los Angeles area, company spokesman Mike Michels said. There, he was key in developing the gas-electric Prius and bringing it to the American market, where it gained popularity for its fuel efficiency.

While much of the car's technology was developed in Japan, Hermance was perhaps the "American father of the Prius" for his tireless work evaluating and promoting it in the U.S., longtime colleague Bill Reinert said.

"When that car came out, no one knew what it was," said Reinert, a Toyota national manager. "Dave dedicated his life to championing this technology."

Hermance joined Toyota in 1991 as a senior manager, the became a general manager in the company's powertrain department. Before that, he worked for General Motors (GM).

"He was widely recognized as the most authoritative individual on hybrid power vehicles in the U.S.," Michels said.

Hermance, who was married with two grown children, was believed to be the only person aboard the plane.

His single-engine plane is classified as experimental by the Federal Aviation Administration. It is based on a Russian design and often is used in aerobatics.

The plane may have taken off from Long Beach but it was unclear where it was heading, Savage said.

The plane was built in 1993 and registered to Yakety Yak, Inc., in Wilmington, Del., the FAA said.

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