AS9120B, ISO 9001:2015, and FAA AC 0056B ACCREDITED

What Is True Altitude and How Is It Measured?

To maintain their heading and adjust for changing conditions, pilots must know the altitude of their aircraft at all times. Aside from ensuring the plane is high enough to avoid obstacles, reaching the correct altitude is important for maintaining the best flight conditions with regards to pressure, temperature, and wind patterns. However, a quick look at the flight display will show that there is more than just one altitude value to consider. So what makes each of these values different? While the central focus of this blog is true altitude, we will also discuss the importance of indicated and absolute altitude. In general, some versions of altitude are more useful during takeoff and landing, while others are best to know when cruising.

While height and altitude are often equated in general conversation, altitude can mean several different things in aviation operations. Firstly, as defined by the Federal Aviation Administration (FAA), true altitude is meant to indicate the height above mean sea level. Often referred to as “sea level,” it is the average surface level of the Earth’s major coastal bodies of water and is also used around the world as a standard measurement. Consequently, true altitude equals the indicated altitude when conditions are normal, which is rarely the case. Instead, the plane will often be flying above terrain that rises above sea level at different heights depending on its area of operation.

To account for the terrain beneath a plane, radio or radar altimeters measure absolute altitude which is the vertical distance of the aircraft above ground level. Specifically, the absolute altitude is true altitude minus terrain elevation, and it is usually measured in feet or meters. This type of altitude is crucial during approach and landing routines as it gives pilots an indication of how far the aircraft is from the ground. Thus, the pilot can be sure to avoid obstacles and be ready for descent at the right time.

Whereas true altitude and absolute altitude are often important to know during a flight, indicated altitude is generally front and center of the vessel. Indicated altitude captures a fairly accurate measurement of one’s current altitude above a fixed level because its reading is given by the altimeter when it is set to the proper atmospheric conditions. The most common type in use today is the barometric altimeter which measures pressure to determine altitude. Often, the altimeter will be set to standard atmospheric conditions so that it will be applicable in most cases.

In conclusion, true altitude is the measure of an aircraft’s height above mean sea level. This reading is often not shown in the flight display, but it can be calculated from indicated altitude or by radar when flying over the ocean. Indicated altitude is the measure shown by the altimeter itself, and it is meant to depict the plane’s altitude with relation to current atmospheric conditions. These conditions will include temperature, wind, clouds, and precipitation. Though it is important to know both indicated altitude and absolute altitude at many different parts of a flight, absolute altitude becomes the most important during approach and landing. By knowing the plane’s approximate altitude above the surface, pilots can be sure to land safely regardless of the elevation, terrain, and man-made structures present before the landing site.

As a device which pilots use to dictate many parts of their flight operations, the altitude indicator, or altimeter, is a crucial component onboard aircraft. Therefore, it is important to conduct regular maintenance and to source high-quality components from the start. Here at Procurement Domain, we are a leading supplier of altitude indicators and other aviation products that have been evaluated for their fit and function on aircraft. Moreover, as we are backed by a supplier network of over 3000 manufacturers, you can rely on our ever-expanding inventory of parts for all the new, used, obsolete, or hard to find items you require. Partner with Procurement Domain for a procurement process that exceeds your high expectations!


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