Russian fighter crews operating the upgraded MiG-31BM practiced intercepting hypothetical enemy aircraft at heights of 6-10 miles, which is equal to the lower stratosphere.
“A pair of fighter aircraft of a similar type acted as ‘enemy’ aircraft. The hypothetical enemy air crews conducted flights at an altitude of 10 km to 15 km and at a speed of 1,000 (621 mph) to 2,500 (1,500 mph) km per hour,” said a report from the Department of Information and Mass Communications of the Russian Defense Ministry.
The exercise involved more than 10 crews, and all targets were “destroyed’ by missiles at a distance of more than 150 km (93 miles), the report said.
The MiG-31BM interceptor aircraft is outfitted with a modern control system and is considered much better than its predecessor, the MiG-31. [source]
The plane can fly at supersonic speeds, and is one of the fastest in the world, achieving top speeds around 2,500 miles per hour. It is an overall upgrade of the MiG-25 Foxbat, a Soviet-era fighter designed as an interceptor. One of its functions today is to intercept cruise missiles and their launch aircraft by reaching missile launch range in the lowest possible time after departing the loiter area.