An Introduction to Altimeters and Altitudes

An altimeter is a device that measures altitude, which can either be the distance above sea level or ground level depending on the type employed. While sometimes used by mountaineers and skydivers, altimeters are most often used by aircraft pilots as an effective way to monitor their height above the ground. The most common types are barometric, meaning the altitude is determined by measuring air pressure. As altitude increases, air pressure decreases, so one can accurately determine their altitude by measuring the air pressure around them. However, it is important to note that weather conditions can alter these pressure readings, as air pressure decreases during storms. Moreover, this is not the only factor that can make an altimeter’s reading inaccurate. For this reason, aircraft pilots typically use five different types of altitude readings.

First, there is the indicated altitude, which is the value shown on the altimeter. This reading can be calculated based on the surrounding air pressure and corrected for local atmospheric conditions by changing its setting. In most cases, if the altimeter is set appropriately, the indicated altitude will be fairly accurate to the actual height of the plane above sea level. However, during nonstandard weather and/or environmental conditions, the indicated altitude may not be completely accurate. As such, there is another form of altitude called true altitude that is meant to be a more exact reading of the vessel’s height above mean sea level. Both of these values are calculated based on the surrounding air pressure, but true altitude is the name given to the actual height of a plane, while the indicated altitude is simply what it is shown to be.

Another measurement based on the surrounding air pressure is pressure altitude which is equal to the indicated altitude when the altimeter is set to 29.92 in Hg. As a standard base value set for all aircraft, the FAA has defined this as such to ensure that all aircraft can fly safely at the same flight level. It is primarily used in performance calculations and high-altitude flights where it is important to know what altitude the aircraft is performing in, in relation to the actual height it is above sea level. As an even more accurate depiction of how well the aircraft is performing, pilots can calculate density altitude which adjusts for nonstandard temperature variations. This is not an actual altitude, but it refers to how an aircraft’s performance will decrease as air pressure decreases as well.

Finally, for situations where it is more important to know the vessel’s height above ground level, rather than sea level, there is absolute altitude. Absolute altitude is read by a radar altimeter. Rather than determining altitude through air pressure readings, a radar altimeter sends a radar signal directly downward from the plane to measure how far away the nearest surface is below it. Knowing the plane’s absolute altitude is especially important during approach and landing because the pilot needs to know when to begin their descent based on the elevation of the landing site. This kind of altitude measurement can also help pilots avoid especially tall terrain and infrastructure if they need to land in an unfamiliar location.

No matter where you plan to fly, having an understanding of different types of altitude variations is a key part to being a great pilot. Regardless of climate and weather conditions, you can be sure of your true altitude in any environment by using information about surrounding air pressure, your distance from sea level, and the altitude which your plane is performing at. Moreover, using the radar altimeter, you can find your distance above the ground during approach and landing. Whatever your needs, if you require aircraft parts for your assembly, you can rely on Jet Aviation Spares with our inventory of over 2 billion new, used, obsolete, and hard-to-find items that have been sourced from accredited manufacturers on our Approved Vendor List (AVL). Begin the procurement process with us today to see all that Jet Aviation Spares can do as your strategic sourcing solution!