4 Fraternity Brothers Die in Small Plane Crash in Illinois Farm Field Under 'Unknown Circumstances'

Four men were killed in a small plane crash in Illinois on Monday.

The four men have been identified as Daniel Shedd, 37, Joshua Sweers, 35, Daniel Schlosser, 39, and John Camilleri, 39, local NBC station KSDK reported Monday.

Shedd's father, Charles Shedd, told the outlet that Sweers, 35, was piloting the plane, a Piper PA28, and that the aircraft had recently passed its inspections and deemed to be in "excellent condition."

The four friends, who had all been in the Phi Gamma Delta fraternity together at Kettering University, took off at 3:19 p.m. on Sunday from the Creve Coeur Airport, which is about 24 miles northeast of St.Louis, Missouri.

RELATED: Atlanta Woman, 23, and Boyfriend, 25, Among 4 Killed When Plane Piloted by His Dad Crashes

Not even 20 minutes later, the plane crashed about 45 miles north, just south of Carlinville, Illinois, at 3:46 p.m., according to KSDK.

It is currently unclear what caused the crash.

The plane crashed in a field near a farmhouse, ABC News reported, and no one else was injured in the accident.

"This was his first time flying with them and I’m not sure if he had ever been in a small plane before," Charles Shedd told KSDK, adding that his son had been "looking forward to the trip."

RELATED: American Pilot, 40, Dies in Plane Crash While Delivering COVID-19 Test Kits to Indonesian Village

The mourning father added to the outlet, "He was the most wonderful son a parent could possibly have."

In a statement on Monday, the Federal Aviation Administration told PEOPLE that the single-engine plane crashed "under unknown circumstances in a large field near Carlinville, Illinois, and that the aircraft was "destroyed upon impact."

The National Transportation Safety Board is in charge of the investigation into the crash, and the FAA is also investigating.