In 1977, Soviet test pilot Alexandr Fedotov took a modified MiG-25 to 37,650 metres or 123,523 feet. Nearly 50 years later, no powered aeroplane in its category has climbed higher. The aircraft was the E-266M, an extreme version of an aircraft already built for speed and altitude. Its two uprated turbojets produced roughly 265 kN of combined after-burning thrust, enough to push it towards Mach 3. Much of the MiG-25 was welded from steel because sustained flight at those speeds produced enough heat to make conventional aluminium construction problematic. But even those engines could not fly it normally to 123,000 feet. Fedotov accelerated beyond 3,000 km/h while there was still enough atmosphere for the engines to breathe, then pulled into a steep zoom climb. As the MiG climbed, it rapidly lost speed, eventually carrying itself upward on an almost ballistic trajectory. At 123,523 feet, barely 0.5% of sea-level air density remains. The sky is darkening, the curvature of the Earth is visible quite well, and there is so little atmosphere that the engines, wings and control surfaces are approaching the limits of what makes an aeroplane an aeroplane. Nearly 50 years have passed. Jet engines have gained digital controls, far more advanced turbine materials and vastly better efficiency, while aircraft themselves have moved into an entirely different technological era. And still, no jet aircraft has climbed beyond Fedotov’s 123,523 feet. That Soviet record from 1977 remains untouched.