Aero Fact: Mach Number vs. True Airspeed
At high altitude, IAS drops while TAS and Mach diverge due to air density changes.
By AircoreDynamics •
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1 min read
Definition: Mach = V/a, while TAS is true local speed; the speed of sound a changes with altitude.
Physics insight: a = √(γRT). As temperature drops, a decreases; the same TAS can correspond to a higher Mach.
Example: At FL350, 270 KIAS ≈ 470 KTAS and ~M0.78; IAS lower while TAS/Mach are higher.
M = V/a,
TAS ≈ KIAS × √(ρ0/ρ) (simplified)
Rules of thumb: Mach limits dominate at altitude; mind MMO.
Common pitfalls: Confusing IAS/CAS/EAS; icing and position errors.
References: EASA/FAA instrumentation notes