A Toyota Motor Corp. 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.

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.