Why did chuck Yeager choose high altitude to try and break the sound barrier?

Answer 1

Safety - more time to recover should something go wrong before making a smoking hole in the ground.

Answer 2

Chuck Yeager chose high altitude to try and break the sound barrier because the thinner air at higher altitudes provides less resistance to the aircraft, allowing it to reach higher speeds. Additionally, at high altitudes, there is less air traffic and fewer obstacles, making it safer to attempt such high-speed flights.