The Importance of the Airspeed Indicator

Within the cockpit of an aircraft, a number of instruments and gauges are available for the pilot to be aware of the operating conditions of the aircraft, allowing them to safely pilot it. For an aircraft to be considered airworthy for certification, it must have a working airspeed indicator. The airspeed indicator, also known as an airspeed gauge, is a flight instrument that provides the speed of an aircraft in km/h, kn, MPH, or m/s. Airspeed indicators are crucial to the safe and efficient operation of an aircraft, and understanding their functionality is beneficial to anyone working with or aspiring to work with aircraft.

To provide accurate readings of airspeed during flight operations, the airspeed indicator utilizes the pitot-static system to measure the difference between dynamic air pressure and static air pressure. Within the case of the airspeed indicator, a metal diaphragm is filled with dynamic pressure from ram air captured by the pitot tube on the aircraft fuselage. Meanwhile, the inner case surrounding the diaphragm contains static air from the static port, and the difference in pressure within the indicator assembly causes an exertion on the diaphragm that is measured by the instrument. As pressure varies with speed, a pointer on the airspeed gauge will move, allowing the pilot to be aware of the current speed. Due to the method of airspeed readings, it is always important to ensure that the pitot tube is always free of debris, as blockage can easily cause the gauge to remain at a zero rating. If the static tube is blocked, on the other hand, readings can still be obtained, but they will most likely be inaccurate.

When reading the airspeed indicator, it is also important to understand the different types of airspeeds that are provided. The indicated airspeed (IAS) is the value that is directly read from the indicator. Despite this, direct readings do not take factors such as air density variations into consideration, or may be inaccurate due to instrument errors. The calibrated airspeed (CAS) accounts for the possible inaccuracies of the airspeed gauge, and charts help iron out any other errors. Lastly, true airspeed (TAS) is the CAS reading that has been further corrected by taking altitude and nonstandard temperatures into consideration. As it is the most accurate, the TAS reading is what is used for flight planning.

If there is a supposed problem with the readings of your airspeed indicator, there are various signs that may denote what your problem may be. If the airspeed indicator displays slowly bleeding levels, reads fast for climbing, and reads slower for descending, the problem may be the pitot line which could be frozen or blocked. If the indicator reads slowly for the level, climb, and descent, then it may be a leak or presence of water in the pitot line. When levels are unaffected, but the climb reads slow and the descent reads fast, then it is most likely a static line problem due to freezing, blockage, or a partial obstruction. Nevertheless, any possible issue with the airspeed indicator or other instruments should always be addressed by a certified repair shop or MRO provider to ensure proper service is given to absolve the problem.

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1. harry walker
2. Posted on October 26, 2020
aviation

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