What Is Mach Number in Aviation?

The 30-second answer

Mach number is the aircraft's true airspeed expressed as a fraction of the local speed of sound. M0.78 = 78% of the local speed of sound.

Why it matters more than knots at altitude

The speed of sound depends on temperature. As an airliner climbs into the cold upper atmosphere, the speed of sound drops, so a constant true airspeed corresponds to a higher Mach number — eventually approaching limits where shock-wave drag spikes.

Typical cruise

• Boeing 787 / Airbus A350: M0.85
• Boeing 737 / Airbus A320: M0.78
• Concorde (historic): M2.0+

See it in FlightyFlow

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