Ma
mach (sea level)
Mach 1 here is 340.294 metres per second, the speed of sound in dry air at 15 °C and standard sea level pressure. It is the reference used for stating aircraft speeds in familiar terms, and it is the value the ISA standard atmosphere gives at sea level.
Watch out: Mach number is properly a ratio, not a speed, and the local speed of sound falls with temperature: about 295 m/s at 11 km altitude, where the stratosphere begins. An aircraft holding Mach 0.85 in the cruise is therefore flying considerably slower over the ground than Mach 0.85 at sea level would be. Treat this fixed value as a sea-level convenience, not as a conversion valid at altitude.
| 1 Ma | 340.294 m/s |
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