Which term refers to flying slower than the speed of sound?

The term that refers to flying slower than the speed of sound is "Subsonic." This designation applies to speeds that are below Mach 1, which is approximately 343 meters per second (or 1,125 feet per second) at sea level in standard atmospheric conditions. Subsonic flight characterizes most commercial aircraft and general aviation flying, where speeds typically range from cruising at around 250 to 600 knots.

In the context of aviation, understanding the different speed classifications is vital. Supersonic describes speeds greater than Mach 1, while transonic refers to speeds that are close to the speed of sound, typically ranging from Mach 0.8 to Mach 1.2. Hypersonic involves speeds exceeding Mach 5, which is significantly higher than subsonic. Each term represents a distinct flight regime with unique aerodynamic challenges and behaviors.