And in that zone, on a typical day, the speed of sound is about 660 mph. That’s also referred to as Mach 1. Mach 2, or twice the speed of sound, would be about 1,320 mph in that altitude range.

Boom Supersonic—the developer of a 64-to-80-passenger commercial airliner that flies faster than the speed of sound—last week set speed and altitude records with its XB-1 test aircraft.

Consequently, while the speed of sound is frequently given as 343 m/s (772 mph, or 1,242 kmph), representing room temperature, airplanes can often break Mach 1 at less than 300 m/s.

Extreme athlete Felix Baumgartner, the first skydiver to fall faster than the speed of sound more than a decade ago, died in ...

Sound travels at 761 mph at sea level but slows with altitude as air temperature goes down and is about 663 mph at 35,000 feet (10,668 meters). Flight 5735 was flying to Guangzhou from Kunming ...