How Airspeed Indicators Work? And The Main Types Of Airspeed

When operating an aircraft, there are various flight characteristics that pilots must consistently monitor and be aware of for both flight efficiency and safety. One of these characteristics is the speed of the aircraft, and this value is used to ensure the aircraft is operating at safe velocities and is following set flight plans for fuel management and scheduling. To measure airspeed, pilots rely on an instrument known as an airspeed indicator (ASI). In this blog, we will discuss how aircraft airspeed indicator functions, as well as the various types of airspeed measurements that can be obtained with their readings.

As is with many aircraft instruments, the aircraft airspeed indicator relies on the pitot-static system for its functionality. Unlike the other instrument types, however, the airspeed indicator relies on both the pitot tube and static port. The pitot tube is used to capture air from the atmosphere, and it is placed directly in the flow of air to measure total pressure. The static port, on the other hand, is placed in a relatively undisturbed area so that static pressure can be obtained.

Within the housing of the airspeed indicator, a diaphragm is present and may be filled with pitot pressure supplied by the pitot tube. A static pressure line is also attached to the housing, allowing for static pressure to fill up the component and surround the diaphragm. As pitot pressure is related to the speed of the vehicle and static pressure is determined by altitude, the difference between the two pressures will result in the diaphragm either expanding or contracting. With an airspeed needle connected to the diaphragm through gears, the needle will move as pressures change to display a reading on the aircraft airspeed indicator.

The airspeed that is directly read off of the aircraft airspeed indicator is known as indicated airspeed (IAS), and it is important to note that this reading has no corrections in place for any air density variations, instrument errors, or installation errors. Once the IAS has been corrected for any errors from installation or instruments, calibrated airspeed (CAS) is obtained. With the use of airspeed calibration charts and other resources, the CAS can be corrected for altitude and nonstandard temperatures, thus obtaining true airspeed (TAS). TAS is important to have, as it is what is used for creating flight plans. In some instances, the flight computer of an aircraft may be able to determine TAS itself.

When reading the airspeed indicator, the most common configurations will display multiple arcs that are colored white, green, yellow, and red. These arcs are ranges of speeds, allowing pilots to know if they can utilize certain equipment or need to reduce their speed. The white arc is the lowest range of speeds, and pilots will fly within this range when they want to safely utilize flaps. The green arc is for normal operations, often being the speed range that pilots will continuously fly in. When approaching the yellow arc, the aircraft is reaching a speed that may warrant caution. Lastly, the red range of speeds is the maximum that the aircraft can reach.

With a reliable aircraft airspeed indicator, pilots can conduct flight operations with ease. Internet of NSN is a trusted online distributor of aircraft parts, and we can help you secure competitive prices and rapid lead-times on countless items that we carry. Upon finding the components that you wish to procure, you may receive quotes for your comparisons by utilizing our RFQ services. Once we have received your request, our team of industry experts will quickly tailor a personalized solution that caters to your unique needs and requirements. Get started today and see why customers choose to rely on Internet of NSN for all their aviation needs.


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