Aircraft Speed Acronyms

This section focuses on differentiating key aviation speed acronyms: True Airspeed (TAS), Indicated Airspeed (IAS), Ground Speed (GS), and Calibrated Airspeed (CAS). Mastery of these concepts is essential for pilots preparing for the CASA RPL theory exam.

Indicated Airspeed (IAS)

Definition: Indicated Airspeed (IAS) is the speed read directly from the aircraft’s airspeed indicator (ASI). It is not corrected for variations in atmospheric pressure, temperature, or instrument errors.

Usage: IAS is a critical parameter for determining specific aircraft performance metrics, such as takeoff, landing, and stall speeds. It relates to the dynamic pressure experienced by the aircraft.

Sources:

• Chapter 8 - FAA
• Airplane Flying Handbook Glossary - FAA

Calibrated Airspeed (CAS)

Definition: Calibrated Airspeed (CAS) is IAS corrected for positional and instrument error. These errors can occur due to pressure loss or variations at the static port or pitot tube.

Notes: CAS closely approximates IAS at higher speeds but can significantly differ at lower speeds where errors are more pronounced.

Sources:

• Chapter 8 - FAA
• Airplane Flying Handbook Glossary - FAA

True Airspeed (TAS)

Definition: True Airspeed (TAS) is the actual speed of the aircraft through the air, corrected from CAS for altitude and nonstandard temperature.

Importance: As altitude increases and air density decreases, IAS becomes less indicative of the aircraft’s actual speed through the air. TAS is crucial for flight planning and navigation.

Calculation: Typically determined using a flight computer with CAS, pressure altitude, and temperature inputs. A rough rule of thumb is to add 2% of CAS per 1,000 feet of altitude.

Sources:

• Chapter 8 - FAA
• Airplane Flying Handbook Glossary - FAA

Ground Speed (GS)

Definition: Ground Speed (GS) is the actual speed of the aircraft over the ground. It is the sum vector of True Airspeed (TAS) and wind velocity.

Adjustment: Adjusted for wind conditions; decreases with a headwind and increases with a tailwind.

Sources:

• Chapter 8 - FAA
• Airplane Flying Handbook Glossary - FAA

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This section provides a concise understanding of the different types of airspeeds and ground speed—critical components needed for safe and effective flight operations. Familiarity with these speed measurements prepares pilots for both theoretical examinations and practical flying scenarios.