{"id":14462,"date":"2025-06-07T16:14:31","date_gmt":"2025-06-07T10:44:31","guid":{"rendered":"https:\/\/ibexaviation.com\/pilot-training\/?p=14462"},"modified":"2026-07-26T10:25:11","modified_gmt":"2026-07-26T04:55:11","slug":"pressure-altimeter","status":"publish","type":"post","link":"https:\/\/ibexaviation.com\/pilot-training\/pressure-altimeter\/","title":{"rendered":"Pressure Altimeter"},"content":{"rendered":"<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i5-pressure-altimeter-1.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<h2>Measurement of Aircraft Altitude using Pressure Altimeter<\/h2>\n<p>A pressure altimeter measures altitude by sensing atmospheric pressure and converting it into a height reading above sea level. Pilots set the local barometric pressure (QNH) to obtain accurate altitude information during flight.<\/p>\n<h3>Introduction to Pressure Altimeter<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i5-pressure-altimeter-2.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The Pressure Altimeter is the primary instrument used to measure aircraft altitude.<\/li>\n<li>It is essentially an <strong>aneroid barometer<\/strong> that measures atmospheric pressure.<\/li>\n<li>The altimeter senses changes in static air pressure and displays them as altitude.<\/li>\n<\/ul>\n<h3>Principle of Pressure Altimeter<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i5-pressure-altimeter-3.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Static (atmospheric) pressure decreases with increasing altitude at a non-uniform rate.<\/li>\n<li>This occurs because the weight of the air column above the aircraft decreases with height.<\/li>\n<li>Static pressure is also affected by variations in temperature and atmospheric pressure.<\/li>\n<li>These variations must be understood and corrected to obtain accurate altitude measurements.<\/li>\n<\/ul>\n<h2>Simple, Sensitive and Servo Assisted Altimeters<\/h2>\n<h3>Construction of a Simple Altimeter<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i5-pressure-altimeter-4.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A simple altimeter consists of a sealed instrument case containing an expandable aneroid capsule.<\/li>\n<li>Static pressure from the aircraft&#8217;s static source is supplied to the sealed instrument case.<\/li>\n<li>The aneroid capsule contains a fixed internal pressure.<\/li>\n<li>As altitude increases, external static pressure decreases, causing the capsule to expand.<\/li>\n<li>The capsule movement is transmitted through a linkage to indicate altitude.<\/li>\n<li>The instrument displays the altitude at which the sensed pressure would exist under International Standard Atmosphere (ISA) conditions.<\/li>\n<\/ul>\n<h3>Manual Setting Knob in a Simple Altimeter<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i5-pressure-altimeter-5.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A manual setting knob is used to adjust the datum altitude by rotating the pointer.<\/li>\n<li>On the ground, the pointer may be set to:\n<ul>\n<li><strong>Zero<\/strong> \u2013 to indicate height above the airfield (Above Ground Level).<\/li>\n<li><strong>Airfield Elevation<\/strong> \u2013 to indicate altitude above Mean Sea Level (MSL).<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h3>Construction of a Sensitive Altimeter<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i5-pressure-altimeter-6.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A Sensitive Altimeter is an improved version of the pressure altimeter.<\/li>\n<li>It uses multiple aneroid capsules to increase sensitivity.<\/li>\n<li>Jewelled bearings reduce mechanical friction.<\/li>\n<li>A temperature-compensating mechanism improves accuracy.<\/li>\n<li>Mechanical vibrators help overcome friction within the instrument.<\/li>\n<li>A variable sub-scale allows selection of the desired pressure datum.<\/li>\n<li>Multiple pointers indicate hundreds, thousands, and tens of thousands of feet for improved readability.<\/li>\n<\/ul>\n<h3>Sub-Scale of a Sensitive Altimeter<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i5-pressure-altimeter-7.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The sub-scale setting is independent of altitude changes and surface pressure variations.<\/li>\n<li>It is used only to select the desired pressure reference (QNH, QFE, or Standard Pressure).<\/li>\n<li>The normal adjustment range is approximately <strong>800 to 1050 hPa<\/strong>.<\/li>\n<\/ul>\n<h3>Construction of a Servo-Assisted Altimeter<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i5-pressure-altimeter-8.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>At higher altitudes, pressure changes become progressively smaller, reducing capsule movement.<\/li>\n<li>A Servo-Assisted Altimeter uses an electromagnetic system known as the <strong>E-I Bar (Electromagnetic Indicator Bar)<\/strong>.<\/li>\n<li>The E-I Bar amplifies very small capsule movements to improve instrument performance.<\/li>\n<\/ul>\n<h3>Advantages of a Servo-Assisted Altimeter<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i5-pressure-altimeter-9.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The E-I Bar generates an electrical error signal for even very small capsule movements.<\/li>\n<li>Reduces or eliminates lag error.<\/li>\n<li>Improves measurement accuracy.<\/li>\n<li>Provides a faster instrument response.<\/li>\n<li>Allows digital altitude display and integration with electronic flight systems.<\/li>\n<\/ul>\n<h3>Calibration of Altimeter<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i5-pressure-altimeter-10.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The altimeter is calibrated according to the <strong>International Standard Atmosphere (ISA)<\/strong>.<\/li>\n<li>It indicates true altitude only when ISA atmospheric conditions exist.<\/li>\n<li><strong>Pressure Altitude<\/strong> is the altitude in the ISA at which the measured atmospheric pressure exists.<\/li>\n<li>For example, if the altimeter senses a pressure of <strong>1013.25 hPa<\/strong>, it will indicate an altitude of <strong>0 ft<\/strong> under ISA conditions.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Measurement of Aircraft Altitude using Pressure Altimeter A pressure altimeter measures altitude by sensing atmospheric pressure and converting it into a height reading above sea level. Pilots set the local barometric pressure (QNH) to obtain accurate altitude information during flight. Introduction to Pressure Altimeter The Pressure Altimeter is the primary instrument used to measure aircraft altitude. It is essentially an aneroid barometer that measures atmospheric pressure. The altimeter senses changes in static air pressure and displays them as altitude. Principle of Pressure Altimeter Static (atmospheric) pressure decreases with increasing altitude&hellip;<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"disable_featured_image":false,"footnotes":""},"categories":[345],"tags":[],"class_list":["post-14462","post","type-post","status-publish","format-standard","hentry","category-cpl-atpl-flight-instruments"],"_links":{"self":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14462","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/comments?post=14462"}],"version-history":[{"count":1,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14462\/revisions"}],"predecessor-version":[{"id":16650,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14462\/revisions\/16650"}],"wp:attachment":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/media?parent=14462"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/categories?post=14462"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/tags?post=14462"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}