Frequently Asked Questions
How is true airspeed related to calibrated airspeed?
TAS ≈ CAS × √(ρ₀/ρ), where ρ is air density at altitude and ρ₀ at sea level standard. A useful rule of thumb: TAS increases ≈ 2% per 1,000 ft of density altitude above sea level.
Why does TAS exceed CAS at altitude?
The airspeed indicator measures dynamic pressure (½ρV²). As ρ drops, the same dynamic pressure (same indicated reading) corresponds to a higher actual V - that higher V is the true airspeed.
A worked example?
At 10,000 ft DA with 120 KCAS: factor ≈ 1 + 0.02 × 10 = 1.20, so TAS ≈ 120 × 1.20 = 144 kt. Exact value via standard atmosphere is ~141 kt - the rule of thumb is within ~2%.
What about Mach effects?
Above Mach 0.3 (≈ 200 KTAS), compressibility makes CAS ≠ EAS, and EAS ≠ TAS by more than the simple density ratio. Use Mach number and POH cruise tables for jet and turboprop altitudes.
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This calculator is for educational and informational purposes only and is not a substitute for official flight or navigation planning. Always use current performance charts, an approved POH/AFM, certified navigation tools, and follow all applicable FAA, ICAO, USCG, and other regulatory guidance. Verify all results independently before operating any aircraft or vessel.