(SACRAMENTO, Calif.) — The drought in California, combined with modern technology, may have uncovered an aviation mystery that has haunted Katherine Radican’s family for more than five decades.

Researchers at an underwater surveying company said a sonar device they have been testing at Folsom Lake, northeast of Sacramento, picked up what appears to be the debris of a small plane that crashed on New Year’s Day in 1965, killing all four people aboard — including Radican’s brother-in-law.

Radican, of El Dorado County, told ABC News on Monday that her late husband, Frank Wilcox, spent most of his life searching the 18-square-mile reservoir that straddles three counties for any sign of the long-lost wreckage that claimed the life of his brother, 15-year-old Glen Amick. She said her husband was only 3 years old when his brother, a standout high school athlete, was killed in the sightseeing flight.

“He didn’t really know his brother, but him and his mom would go out to the lake periodically when the water was low and look around to see if they could see anything,” Radican said of her husband, who passed away nearly three years ago.

She said that before Wilcox’s mother died around 17 years ago, he made her a vow that he would keep searching for his brother’s remains and perhaps finally give him a proper burial.

“He promised her that he would find him for her,” Radican said.

Jeff Riley and Tyler Atkinson, researchers for Seafloor Systems, Inc., said they were recently out on the receding Folsom Lake testing their newest underwater sonar technology when they made a startling discovery.

“I saw something that was not normal,” Atkinson told ABC station KGO-TV in San Francisco.

He said the new sonar equipment picked up on something artificial in the deepest part of the lake, but the water was too murky to tell what it was.

“He sees something on the bottom like this that looks man-made,” added John Tamplin, president of Seafloor Systems. “That’s when we decide, OK there’s definitely something down there, and maybe it’s the plane.”

Riley and Atkinson returned to the same spot on the lake last week with a small remote-operated underwater vessel, or ROV, and sent it down about 160 feet to take a closer look. But the water was too cloudy to see anything beyond six or seven feet, they said.

They went back a third time with a sonar device attached to the ROV and said they were astonished by the images it dispatched to the surface.

Tamplin said they could see “as clear as day” the image of an almost fully intact Piper Comanche 250 covered in silt. While the fuselage, the engine, propeller, right wing and tail were visible, they could not make out the aircraft’s number or see inside the cockpit.

The wreckage of a 1965 plane crash of a Piper Comanche 250 in Folsom Lake may have just been identified by researchers, using underwater sonar surveying equipment and low lake levels at the dam, outside of Sacramento. https://t.co/hddX54qsVA pic.twitter.com/zbLgegDiQG

— ABC7 News (@abc7newsbayarea) June 14, 2021

The researchers said the lake’s low water level helped them make the discovery of what they now suspect is the plane lost 56 years ago.

“I think it’s definitely a rewarding prospect to offer some sort of closure” to the families of those who perished, Riley told KGO.

Due to the drought in California, Folsom Lake, which has the capacity to hold 975,000 acre-feet of water, is down to about 361,000 acre-feet of water, or about 37% of capacity, according to California Department of Water Resources data released in May.

Radican told ABC News that the plane was found at the bottom of what used to be a section of the American River before Folsom Dam was built in 1955. She said her late husband had searched the area during a drought in 2014 with the help of a different sonar company but came up empty-handed.

Lt. Nelson Resendes of the Placer County Sheriff’s Office told ABC News on Monday that the plane was located in an area of the lake that is on the Placer County-El Dorado County line. He said his agency has opened an investigation and is putting together a “game plan” to send divers down to the wreckage to recover any human remains and determine how to salvage the wreckage.

The plane carrying Wilcox’s brother on his first flight collided in midair with a small Beechcraft Debonair sightseeing plane at an altitude of about 2,500 feet, the Roseville Press Tribune reported at the time.

Despite being damaged, the Beechcraft managed to make a successful emergency landing at a local airport, but the Piper Comanche plummeted into the lake and disappeared, the newspaper reported. Rescue crews recovered the body of the pilot of the Piper Comanche, but there was no trace of the aircraft and its three passengers.

In a 2014 interview with KTXL-TV in Sacramento, Wilcox spoke of his mission to find his brother, telling the station, “I’m going to find him and get him out of here.”

“He took a plane ride,” Wilcox said of his brother, “and that was the last thing he ever did.”

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