Per the Department of Defense:
On Nov. 5, 2018, a U.S. EP-3 Aries aircraft flying in international airspace over the Black Sea was intercepted by a Russian SU-27. This interaction was determined to be unsafe due to the SU-27 conducting a high speed pass directly in front of the mission aircraft, putting at risk the pilots and crew. The intercepting SU-27 made an additional pass, closing with the EP-3 and applying its afterburner while conducting a banking turn away. The crew of the EP-3 reported turbulence following the first interaction, and vibrations from the second. The duration of the intercept was approximately 25 minutes.
While the Russian military is within its right to exercise within international airspace, this interaction was irresponsible. We expect them to behave within international standards set to ensure safety and to prevent incidents, including the 1972 Agreement for the Prevention of Incidents On and Over the High Seas (INCSEA). Unsafe actions increase the risk of miscalculation and potential for midair collisions.
The U.S. aircraft was operating in accordance with international law and did not provoke this Russian activity.
Watch footage of the intercept below: