Quick Facts
- Type
- Performance Parameter
- Definition
- The ratio of an aircraft's true airspeed to the local speed of sound
- Used By
- Pilots, Engineers
Definition#
Mach number is the ratio of an aircraft's true airspeed to the local speed of sound. Mach 0.80 means the aircraft is traveling at 80% of the speed of sound. The speed of sound varies with temperature (approximately 661 knots at sea level ISA).
Why It Matters Operationally#
At high altitude, jets fly at a target Mach number (typically Mach 0.78–0.85) rather than IAS. Flying too fast risks encountering compressibility effects (Mach buffet); too slow risks low-speed buffet. The coffin corner narrows this margin at very high altitudes.
Related Guides#
- How Jet Engines Work (Turbofan vs Turboprop)
- How Airplanes Fly — The Complete Aviation Fundamentals Guide