An in-flight emergency caused a Ukrainian Su-27 fighter jet to crash last month during Exercise Clear Sky, killing both an American and Ukrainian pilot, the head of the Ukrainian air force said Thursday.
The Su-27UB Flanker-C, which was on a routine flight as part of the U.S. Air Force-led drills, experienced "an emergency situation that brought it to a catastrophe," said Colonel-General Sergii Drozdov, commander of the Ukraine air force.
Lt. Col. Seth "Jethro" Nehring, a fighter pilot with the California Air National Guard's 194th Fighter Squadron, out of the 144th Fighter Wing, and Col. Ivan Petrenko, deputy commander of the East Air and chief of aviation from Ozern Air Base in Zhytomer, Ukraine, were killed in the Oct. 16 crash.
"The Minister of Defence of Ukraine assigned the investigation board, and now the investigation board is ongoing," Drozdov said through a translator Thursday at the Pentagon.
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He noted the U.S. Air Force is also investigating and observing the Ukrainian investigation "openly." The incident occurred in the Khmelnytskyi region of western Ukraine.
Drozdov visited the Defense Department to meet with his counterpart, Air Force Chief of Staff Gen. David Goldfein. The two highlighted the progress made during the exercise last month at Ukraine's Starokostiantyiv Air Base, despite the fatal crash.
"The exercise showcased the strong bond between the U.S. and Ukraine, and how far the Ukrainian air force has come in their paths toward NATO interoperability," Goldfein said during a press event.
On Thursday, they took it a step further, outlining a five-year plan to expand future cooperation between their air forces, they said.
"Russia's aggression is not simply a matter for Ukraine," Goldfein said. "It's a threat to the region, to Europe, to the United States, to the stability of international order."
He added, "If there's one message I want to get through loud and clear, it's that America remains steadfast in our support for Ukraine's sovereignty and for its territorial integrity."
Last month's exercise -- which marked the 25th anniversary of the longstanding State Partnership Program between the California Guard and Ukraine -- was designed as a stepping-stone to understanding higher-complexity flight operations, officials told Military.com. It was intended, they said, to enable Ukraine to integrate with other partners to keep up its slow but steady military flight achievements.
Drozdov said the goal is to deter forces that have been flowing into the eastern part of the country since Crimea's seizure in 2014.
Additional integration with U.S. forces would help stifle Russia's gains, he said.
When asked if future planning includes training the Ukrainian air force how to counteract Russian forces aerially in the eastern region, Goldfein said, "It does."