Keep an eye on the seat-back display during the first 20 minutes or so after takeoff, and you'll see that as your flight climbs, the air temperature plummets. At altitudes near 10.5 km (roughly 35,000 feet), the outside temperature hovers near -50 degrees C. For a common commercial plane traveling around 920 km/hour, that bitter-cold air is enough to cool the exterior of an aircraft as it cuts through the sky. An ultrafast military jet traveling at more than three times that speed, however, creates such friction with the surrounding air that those frigid temperatures don't do enough to cool the aircraft and prevent possible damage to equipment.