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The Different Types of Airspeed in Aviation Explained

Airspeed is one of the most important performance measurements in aviation. It influences everything from takeoff and landing distances to stall speeds, navigation, and fuel efficiency. But for student pilots, it can also be confusing—there isn’t just one kind of airspeed. Instead, pilots reference different types depending on the context and the corrections applied.


The four most common types of airspeed you’ll encounter are: Indicated Airspeed (IAS), Calibrated Airspeed (CAS), True Airspeed (TAS), and Groundspeed (GS). Each has its unique meaning and use in flight.



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Indicated Airspeed (IAS)

Definition: Indicated airspeed is the speed shown directly on the aircraft’s airspeed indicator, without correction for instrument or position errors.

Key Points:

  • IAS is derived from the pitot-static system, which measures the difference between dynamic and static pressure.

  • It’s the most basic and immediate reference available to pilots.

  • Airplane operating limitations (like stall speeds, maneuvering speeds, and flap extension speeds) are published in IAS.

When it matters:

  • Used for maintaining safe flight, following aircraft limitations, and adhering to ATC instructions.

  • IAS is always referenced in the cockpit during maneuvers.


Calibrated Airspeed (CAS)

Definition: Calibrated airspeed is indicated airspeed corrected for instrument error and position error (caused by the airflow around the pitot tube and static ports).

Key Points:

  • At most speeds, IAS and CAS are very close, but differences become more noticeable at slower airspeeds and high angles of attack.

  • Aircraft manufacturers provide charts or correction tables in the Pilot’s Operating Handbook (POH) to convert IAS to CAS.

When it matters:

  • CAS provides a more accurate reference for performance charts and flight testing.

  • Still not the "real speed" through the air, but closer than IAS.


True Airspeed (TAS)

Definition: True airspeed is the actual speed of the aircraft through the surrounding air mass.

Key Points:

  • TAS is CAS corrected for altitude and non-standard temperature.

  • As altitude increases, air density decreases, which means IAS reads lower even though the airplane is moving faster through the air.

  • Pilots calculate TAS using an E6B flight computer, onboard avionics, or modern glass cockpit systems.

When it matters:

  • Used for flight planning, navigation, and fuel burn calculations.

  • TAS is what you would use to determine how long it will take to fly a specific distance through the air.


Groundspeed (GS)

Definition: Groundspeed is the aircraft’s actual speed across the ground, factoring in the effect of wind.

Key Points:

  • Groundspeed is TAS adjusted for wind.

  • With a tailwind, GS is higher than TAS. With a headwind, GS is lower than TAS.

  • Groundspeed can be calculated with navigation equipment such as GPS or by applying wind correction formulas during planning.

When it matters:

  • Used for determining time en route and actual progress over the ground.

  • Crucial for cross-country navigation and fuel management.


Putting It All Together

  • Indicated Airspeed (IAS): What you see on the airspeed indicator.

  • Calibrated Airspeed (CAS): IAS corrected for instrument and position error.

  • True Airspeed (TAS): Actual speed through the air mass, corrected for altitude and temperature.

  • Groundspeed (GS): Actual speed over the ground, factoring in wind.


For example, at 8,000 feet on a warm day, a pilot may see an indicated airspeed of 110 knots, which converts to a calibrated airspeed of 112 knots. After adjusting for altitude and temperature, the true airspeed might be 130 knots. With a 20-knot headwind, the airplane’s groundspeed would only be 110 knots.


Final Thoughts

Understanding the different types of airspeed is essential for safe and efficient flying. IAS keeps pilots within the aircraft’s operating envelope, CAS provides accuracy, TAS helps with flight planning, and GS tells you how quickly you’ll reach your destination.


Mastering these concepts not only makes you a more knowledgeable pilot but also a safer and more precise one.



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