Airspeed Calibration & Error Solver (IAS, CAS, EAS, TAS & Mach)
Convert Indicated Airspeed (IAS) to Calibrated (CAS), Equivalent (EAS), True Airspeed (TAS), and Mach.
Last reviewed by the myCalculator Editorial Team
Input Parameters
Instrument and position correction from aircraft POH calibration chart
Calculation Results
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Formula & How Airspeed Calibration & Error Solver (IAS, CAS, EAS, TAS & Mach) Works
The airspeed indicator shows IAS, which is converted in steps: IAS plus the instrument and position error gives CAS, correcting CAS for compressibility gives EAS, and correcting for air density gives TAS. With an IAS of 120 knots and a 2-knot position error, CAS is 122 knots. At 8,500 ft pressure altitude and 5°C, the air is thinner, and a rule of thumb of 2% per 1,000 ft gives a TAS of about 122 × 1.17 = 143 knots. Mach number is TAS divided by the local speed of sound. TAS is what you need for navigation and flight planning, while IAS is what drives the aircraft's handling and stall speed, so keep both in mind.
- Enter Indicated Airspeed / IAS (knots) (KIAS): Input your target parameter value.
- Enter Pitot-Static Position / Instrument Error (knots) (kts): Input your target parameter value.
- Enter Pressure Altitude (ft) (ft): Input your target parameter value.
- Enter Outside Air Temperature / OAT (°C) (°C): Input your target parameter value.
- Apply Formula: Calculate using
CAS = IAS + Error | EAS = CAS × [1 - 0.5(1-δ)M²] | TAS = EAS / √σ | Mach = TAS / a. - Review Results: View exact computed answers, metrics, and worked mathematical proofs.
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Frequently Asked Questions (FAQs)
Why is True Airspeed higher than Indicated Airspeed at altitude?
Because air density decreases with altitude, fewer air molecules enter the pitot tube for a given speed. The aircraft must fly faster through the air (higher TAS) to generate the same dynamic pressure reading on the ASI (IAS). TAS increases roughly 1.5% to 2% per 1,000 ft of altitude.
When does compressibility become significant?
Compressibility effects become noticeable above 200 knots and significant above Mach 0.4 (approx 250 KTAS), where ram air compression in the pitot tube causes the ASI to read slightly higher than actual Equivalent Airspeed.
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Authoritative Standards & Verified Reference Citations
Calculations and mathematical logic on this page are grounded in published statutory rules, regulatory standards, and official government data published by the following bodies:
CASR Part 91 general operating and flight rules, Part 121 fuel reserves, and flight crew licensing standards.
Aviation weather services, standard atmosphere (ISA) profiles, METAR/TAF aerodrome weather reports.
Aeronautical Information Publication (AIP), En Route Supplement Australia (ERSA), and airspace procedures.
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Operational Scenario
Operational Scenario: VFR Coastal Transit Beneath Melbourne Class C Steps
You are routing VFR southbound along the Port Phillip coastline. The controlled airspace above steps down from 4,500 ft to 2,500 ft, and then to 1,500 ft near a Class D control zone. Air transport arrivals are descending through 3,000 ft in the Class C airspace just above you.
Practical Decisions
- •Plan to stay clearly below the lower limit of each controlled-airspace step, with a buffer for altimeter and navigation error, unless you hold an ATC clearance.
- •Altimeter discipline: set the current area QNH. An error of 10 hPa is roughly 300 ft of altitude — enough to put you inside a step.
- •If your aircraft has a serviceable transponder, it must be active at all times in flight, with Mode C (altitude) operating continuously if fitted (AIP ENR 1.1 para 10.5.1).
- •Check prohibited, restricted and danger (PRD) areas and their activation times in the Designated Airspace Handbook, ERSA and NOTAMs before you fly.
Knowledge Check
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