The Air Force on Wednesday identified the American pilot killed in a crash of a Ukrainian Su-27 aircraft as Lt. Col. Seth “Jethro” Nehring, of the California Air National Guard.

A Ukrainian pilot, Col. Ivan Petrenko, was also killed in Tuesday’s crash, the Air Force said. Petrenko was deputy commander of the East Air, chief of aviation, from Ozern Air Base in Zhytomer, Ukraine.

Nehring was a fighter pilot with the California Guard’s 194th Fighter Squadron, part of the 144th Fighter Wing out of Fresno.

He served with the 144th for 20 years, the Air Force said, beginning his career as an enlisted crew chief before being selected for a pilot slot and becoming an officer. He flew the F-16 Viper for 15 years and later switched to the F-15 Eagle.

"We are a close-knit family, and when a tragedy like this occurs, every member of the 144th Fighter Wing feels it,” Col. Daniel Kelly, commander of the 144th, said in the release. “We share in the sorrow felt by Jethro’s loved ones, and our thoughts and prayers go out to his family and friends, as well as those of the Ukrainian aviator.”

The Air Force said Nehring and Petrenko were on a routine familiarization training flight when their aircraft crashed in the Khmelnytskyi region of Ukraine, about 175 miles southwest of the capital city of Kyiv.

They were taking part in Ukraine’s Clear Sky exercise, which aims to increase the interoperability of NATO countries and partner nations’ air forces. About 950 service members from nine militaries are taking part in the exercise, including the United States, United Kingdom, Ukraine, Belgium, Denmark, Estonia, the Netherlands, Poland and Romania.