At what altitude must aircraft adhere to Mach 1 speed limit?

Aircraft must adhere to the Mach 1 speed limit above 10,000 feet because this altitude is where the effects of compressibility become significant and where the potential for breaking the sound barrier occurs. The regulations set forth by aviation authorities, such as the Federal Aviation Administration (FAA) in the United States, establish that aircraft should not exceed a speed of Mach 1 (approximately 1,174 km/h or 730 mph at sea level) when flying at altitudes above this level to ensure safety and to minimize the risk of sonic booms in populated areas.

At altitudes below 10,000 feet, various aircraft operations, including general aviation activities, are left relatively unrestricted in speed to facilitate flight training and standard operations without compromising safety measures for the populated areas on the ground. Therefore, the context of aviation regulations regarding speed limits is crucial, and understanding the implications of flying at different altitudes helps maintain safety and compliance in the skies.