A Minnesota doctor was found dead in the wreckage of a private airplane Thursday morning south of Duluth, more than 12 hours after the flight failed to arrive at its destination in the Twin Cities.

The single-engine plane, bound for the Crystal Airport, was located in a river about 7 a.m. northwest of the runway of the Moose Lake Carlton County Airport following a search and rescue operation, the Sheriff’s Office said.

The pilot was identified as Thomas Stillwell, 65, of Plymouth. Stillwell, a well-known urologist associated with North Memorial and Fairview health systems, was recently named a Top Doctor by Mpls.St. Paul Magazine.

He was a Navy veteran who served as a surgical field medic in the Gulf War and had for decades flown to rural communities such as Sandstone, Moose Lake and Grantsburg, Wis., to treat patients.

“I love to fly,” he said in a 2016 interview with Minnesota Flyer. “I think being a pilot is part of your genetics. It’s somewhere deep in you that, once it gets tapped, it’s kind of hard to resist. You must feed this need. If you don’t, you’re not happy.”

Randy Ciche, head of maintenance at the Moose Lake airport, said the plane was routinely used by Stillwell to do medical outreach around the state.

Map: Carlton County Airport and Crystal Airport Map: Carlton County Airport and Crystal Airport

Investigators from the Federal Aviation Administration (FAA) and the National Transportation Safety Board will work to determine the cause of the crash.

Weather in the area at the time was not ideal for flying, according to the National Weather Service. Rain was changing to heavy snow, dropping visibility to less than a mile, said meteorologist Chris O’Brien.

Sustained winds of 10 mph were gusting up to roughly 20 mph, O’Brien added.

The plane had a flight plan filed with a 4:30 p.m. departure Wednesday from the Moose Lake and a 5:15 p.m. arrival planned in Crystal, according to the Sheriff’s Office.

After the scheduled arrival time passed, the FAA contacted authorities in Carlton County and neighboring Pine County to the south.

That notification set off searches of airports in Cloquet, Moose Lake and Hinckley by sheriff’s deputies from Carlton and Pine counties.

Radar for major airports in Duluth and the Twin Cities failed to pick up the plane.

The 32-year-old Mooney M20J is registered with the FAA as being owned by the nonprofit Club Cherokee and has the Crystal Airport as its address.

“The Minnesota aviation community is a close-knit family, and any time there is an aircraft incident, we are all affected,” club manager Bruce Killam said in a statement Thursday afternoon. “The pilot … was a long-standing and highly regarded member of Club Cherokee.”