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How does an altimeter work?

Updated: Feb 10, 2023

An altimeter is a key instrument in an aircraft that measures the altitude of the aircraft above sea level. It provides information on the aircraft's height above the ground, which is crucial for navigation, takeoff and landing.


There are two main types of altimeters: barometric and radar.


A barometric altimeter works by measuring changes in atmospheric pressure to determine altitude. It consists of a sealed aneroid capsule that expands or contracts with changes in atmospheric pressure, which is transmitted to the altimeter's dial through a series of gears.

As the aircraft climbs, the atmospheric pressure decreases, causing the aneroid capsule to expand and rotating the altimeter's dial to indicate a higher altitude. Conversely, as the aircraft descends, the atmospheric pressure increases, causing the capsule to contract and rotating the dial to indicate a lower altitude.


A radar altimeter works by emitting a radar signal towards the ground and measuring the time it takes for the signal to bounce back. This time is used to calculate the distance from the ground, which is then displayed as altitude on the altimeter.


Radar altimeters are commonly used in modern aircraft, especially during takeoff and landing when the altitude is changing rapidly. They provide a more accurate measurement of altitude, especially when flying at low altitudes over uneven terrain, as they are not influenced by changes in atmospheric pressure.


In summary, an altimeter is a critical instrument in an aircraft that provides information on the aircraft's altitude above sea level. The two main types of altimeters are barometric and radar, and they work by measuring changes in atmospheric pressure or by emitting a radar signal to determine the altitude.


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