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What is CAS in Aviation? (Calibrated Airspeed)

Updated: February 19, 2024

Understanding Calibrated Airspeed (CAS) in Aviation

Aviation is a complex and fascinating field that involves several technical terms and concepts. One such term is calibrated airspeed (CAS), which plays a crucial role in flight operations. In this article, we will delve into the details of calibrated airspeed, its significance, and how it is calculated. So buckle up and get ready to explore the world of CAS!

What is Calibrated Airspeed (CAS)?

Calibrated airspeed (CAS) refers to the airspeed reading displayed on an aircraft's airspeed indicator after it has been adjusted for instrument and position errors. It is the speed at which an aircraft is moving through the air, corrected for various factors that affect the accuracy of the measurement.

Unlike indicated airspeed (IAS), which is the uncorrected reading directly from the airspeed indicator, calibrated airspeed compensates for instrument errors such as mechanical friction, position errors caused by the location of the pitot-static system, and installation errors due to the aircraft's design. By applying these corrections, calibrated airspeed provides a more accurate measure of an aircraft's true airspeed.

To calculate calibrated airspeed, the airspeed indicator is adjusted using a calibration card or table specific to the aircraft. This card takes into account the known errors associated with the particular aircraft's instruments and position. By applying the correction factors from the calibration card, the airspeed indicator can display an accurate calibrated airspeed reading.

Importance of Calibrated Airspeed in Aviation

Calibrated airspeed is a critical parameter in aviation as it directly affects the aircraft's performance and safety. Here are a few reasons why calibrated airspeed is significant:

Performance Calculation: Calibrated airspeed is used to determine an aircraft's true airspeed, which is essential for various performance calculations, including fuel consumption, range, and time en route. These calculations rely on accurate airspeed data to provide pilots with vital information for flight planning and decision-making.
Flight Instrument Accuracy: Aircraft instruments, including altimeters, vertical speed indicators, and flight management systems, depend on calibrated airspeed for precise measurements. By using calibrated airspeed instead of indicated airspeed, these instruments can provide accurate readings to pilots, enabling them to navigate and control the aircraft more effectively.
Compliance with Limitations: Aircraft have specific limitations and operating conditions that must be adhered to for safe operation. Many of these limitations, such as maximum speed limits, maneuvering speed, and stall speed, are specified in terms of calibrated airspeed. Pilots rely on calibrated airspeed to ensure they stay within these limits and operate the aircraft safely.

As we can see, calibrated airspeed is a crucial parameter that influences various aspects of aviation, from performance calculations to instrument accuracy and compliance with operational limitations.

Calculating Calibrated Airspeed

To calculate calibrated airspeed, pilots and aircraft technicians follow a specific procedure that involves using the aircraft's calibration card or table. Here's a step-by-step guide to the process:

Obtain the Calibration Card: Each aircraft has a specific calibration card or table that provides the necessary correction factors for the airspeed indicator. This card is typically provided by the aircraft manufacturer and is specific to the aircraft's instruments and position errors.
Collect Relevant Information: Gather the current atmospheric conditions, including altitude, temperature, and pressure. These factors can influence the accuracy of the airspeed indicator and must be taken into account during the calibration process.
Apply Correction Factors: Using the information from the calibration card and the atmospheric conditions, apply the appropriate correction factors to the indicated airspeed. This involves adjusting for instrument errors, position errors, and any other known discrepancies.
Read the Calibrated Airspeed: Once the correction factors have been applied, the airspeed indicator will display the calibrated airspeed. This reading provides a more accurate measure of the aircraft's true airspeed.

It is important to note that the calibration card and correction factors are unique to each aircraft. Pilots and technicians must ensure they are using the correct information for their specific aircraft to obtain accurate calibrated airspeed readings.

Calibrated airspeed (CAS) is a critical parameter in aviation that provides accurate airspeed measurements by compensating for instrument and position errors. Its importance lies in its role in performance calculations, flight instrument accuracy, and compliance with operational limitations. By following the appropriate calibration procedure, pilots and technicians can ensure the accuracy of calibrated airspeed readings, enabling safe and efficient flight operations.

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