Civilian airliners fly very public routes, and it behooves states not to interfere with those flights with any military or surveillance craft. It’s best for safety, and not doing so risks calling attention to their activity.
One of NATO’s CL-600 spy planes forced two aircraft to change course because it got in the way. The bigger of the two was a Russian airliner headed to Moscow from Tel Aviv, which had to drop below 2,000 feet to safely cross.
Another smaller craft, flying from Sochi to Skopje, was also forced to change course. Russia did not identify which NATO nation the CL-600 belonged to. Such planes are principally in the operation of the US, Britain, and Canada.
That wasn’t even the only incident over the Black Sea on Fridasy. Russia also reported that their air force intercepted a US spy plane in the area. The US plane, a RC-135, was chased out of the area by Su-27 and Su-30 fighters.
This is a regular occurance, where US/UK RC 135 spy planes fly around the Black Sea off the coast of Crimea and Russia, yet we only hear about so called Russian aggression.