{"id":14464,"date":"2025-06-07T16:14:49","date_gmt":"2025-06-07T10:44:49","guid":{"rendered":"https:\/\/ibexaviation.com\/pilot-training\/?p=14464"},"modified":"2025-06-09T19:30:03","modified_gmt":"2025-06-09T14:00:03","slug":"altimetry","status":"publish","type":"post","link":"https:\/\/ibexaviation.com\/pilot-training\/altimetry\/","title":{"rendered":"Altimetry"},"content":{"rendered":"\n<h2>Altimetry<\/h2>\n\n\n\n<h3>Height Above Mean Sea Level<\/h3>\n\n\n\n<ul><li>Mean sea level (MSL) is the reference sea level taking the average of tides<\/li><li>MSL is the datum for measuring altitude and elevation<\/li><li>Altitude is the vertical distance of a movable object from MSL<\/li><li>Elevation is the vertical distance of a point on surface of earth from MSL<\/li><li>Altitude and elevation are referred as Above mean sea level (AMSL)<\/li><\/ul>\n\n\n\n<h3>Height Above Ground Level<\/h3>\n\n\n\n<ul><li>Airfield Reference Point (ARP) is the reference point for an airfield<\/li><li>Height is the vertical distance from specified datum<\/li><li>ARP is the datum for measuring height above ground in an airfield<\/li><li>Height above an airfield is referred as Above ground level (AGL)<\/li><\/ul>\n\n\n\n<h3>Pressure Altitude and Flight Levels<\/h3>\n\n\n\n<ul><li>Standard Pressure Setting (SPS) is the pressure at MSL as per ISA<\/li><li>Value of standard pressure setting is 1013.25 hPa<\/li><li>Pressure altitude is the altimeter reading when altimeter subscale is set to SPS<\/li><li>Flight levels are levels of constant pressure<\/li><li>Vertical separation between each flight level corresponds to 500 ft<\/li><li>Flight level of 050 (FL 050) means a pressure altitude of 5000 feet<\/li><\/ul>\n\n\n\n<h3>Use of Datum Setting for Pressure Altimeter<\/h3>\n\n\n\n<ul><li>Height indicated on the altimeter, is the height above set datum pressure as per International Standard Atmospheric conditions<\/li><li>For example, when datum pressure is set to 1000 hPa on altimeter sub scale<\/li><li>Altimeter compares the prevailing pressure to the datum pressure setting<\/li><li>Converts the pressure difference to height as per ISA conditions<\/li><li>Points to this height to the pilot on a circular dial<\/li><\/ul>\n\n\n\n<h3>QFE<\/h3>\n\n\n\n<ul><li>QFE is the observed pressure reduced to ARP using ISA lapse rate<\/li><li>It is the atmospheric pressure on ground at an airfield<\/li><li>If QFE is set as datum<\/li><li>On ground, the altimeter reads nearly zero on the runway<\/li><li>During flight, altimeter indicates height above ground level (AGL)<\/li><\/ul>\n\n\n\n<h3>QNH<\/h3>\n\n\n\n<ul><li>QNH is the observed pressure reduced to MSL using ISA lapse rate<\/li><li>It is the same lapse rate by which altimeters are calibrated<\/li><li>When QNH is set on subscale<\/li><li>On Ground, altimeter will indicate elevation of airfield<\/li><li>During flight, the altimeter would read altitude<\/li><li>Altitude is the height above mean sea level<\/li><\/ul>\n\n\n\n<h3>SPS<\/h3>\n\n\n\n<ul><li>Standard Pressure Setting (SPS) is the pressure at MSL as per ISA<\/li><li>Value of standard pressure setting is 1013 hPa<\/li><li>Pressure altitude is the altimeter reading when altimeter subscale is set to SPS<\/li><\/ul>\n\n\n\n<h3>Flight Level<\/h3>\n\n\n\n<ul><li>Flight levels are levels of constant pressure<\/li><li>Vertical separation between each flight level corresponds to 500 ft<\/li><li>Flight level of 050 (FL 050) means a pressure altitude of 5000 feet<\/li><\/ul>\n\n\n\n<h3>QNE &#8211; SPS<\/h3>\n\n\n\n<ul><li>QNE is the the height indicated on airfield when standard pressure setting of 1013 is set on altimeter<\/li><li>Used at high altitude airfields where setting QFE is not possible<\/li><li>Out of range of altimeter sub-scale<\/li><\/ul>\n\n\n\n<h3>Transition Altitude during Climb Phase<\/h3>\n\n\n\n<ul><li>It is that altitude during climb out phase where an the altimeter<\/li><li>Has to be reset to SPS (1013 hPa)<\/li><li>Varies from one airfield to another<\/li><li>Does not vary from time to time<\/li><\/ul>\n\n\n\n<h3>Altimeter indications During Climb at Transition Altitude<\/h3>\n\n\n\n<ul><li>If the altimeter changes over from high QNH (1030) to SPS (1013)<\/li><li>Altimeter shows sudden decrease in altitude<\/li><li>If the altimeter changes over from low QNH (1000) to SPS (1013)<\/li><li>Altimeter shows sudden increase in altitude<\/li><\/ul>\n\n\n\n<h3>Transition Level during Descent Phase<\/h3>\n\n\n\n<ul><li>It is that altitude during descent phase where an the altimeter<\/li><li>Has to be reset to the local QNH<\/li><li>Varies from one airfield to another<\/li><li>Varies from day to day<\/li><\/ul>\n\n\n\n<h3>Altimeter Indication at Transition Level during Descent<\/h3>\n\n\n\n<ul><li>If the altimeter changes over from SPS (1013) to high QNH (1020)<\/li><li>Altimeter shows increase in altitude<\/li><li>If the altimeter changes over from SPS (1013) to low QNH (1000)<\/li><li>Altimeter shows decrease in altitude<\/li><\/ul>\n\n\n\n<h3>Transition Layer<\/h3>\n\n\n\n<ul><li>Transition layer is the airspace of vertical dimensions between<\/li><li>Transition Altitude &amp; Transition level<\/li><\/ul>\n\n\n\n<h3>Calculation of QNH From QFE<\/h3>\n\n\n\n<ul><li>Airfields below 5000 feet<\/li><li>Add 1 hPa change for every 27 feet elevation<\/li><li>Airfields above 5000 feet<\/li><li>Add 1 hPa change for every 25 feet elevation<\/li><\/ul>\n\n\n\n<h3>Density Altitude<\/h3>\n\n\n\n<ul><li>Density altitude is that altitude in ISA where prevailing density is found<\/li><li>Density altitude is quite similar to Pressure altitude<\/li><li>Which is that altitude in ISA where prevailing pressure is found<\/li><li>In ISA conditions Pressure altitude and Density altitude would be same<\/li><li>Density Altitude is important for calculating Aircraft performance<\/li><li>Lower Density altitude good aircraft performance<\/li><li>Higher Density altitude bad aircraft performance<\/li><\/ul>\n\n\n\n<h3>Air Density in High Hot and Humid Atmosphere<\/h3>\n\n\n\n<ul><li>Air density would be lesser in these conditions<\/li><li>High altitude<\/li><li>Warmer than ISA<\/li><li>High Humidity<\/li><li>Lower air density means higher density altitude<\/li><\/ul>\n\n\n\n<h3>Calculation of Density Altitude<\/h3>\n\n\n\n<ul><li>Increased Density altitude results in poor aircraft performance<\/li><li>For example, Take-off run required would increase<\/li><li>Ensure performance parameters before take-off roll<\/li><li>Density Altitude can be found from calculation of ISA Deviation<\/li><li>Density altitude = Pressure altitude + (120 \u00c3\u2014 ISA deviation)<\/li><\/ul>\n\n\n\n<h2>Share this Page<\/h2>\n","protected":false},"excerpt":{"rendered":"<p>Altimetry Height Above Mean Sea Level Mean sea level (MSL) is the reference sea level taking the average of tides MSL is the datum for measuring altitude and elevation Altitude is the vertical distance of a movable object from MSL Elevation is the vertical distance of a point on surface of earth from MSL Altitude and elevation are referred as Above mean sea level (AMSL) Height Above Ground Level Airfield Reference Point (ARP) is the reference point for an airfield Height is the vertical distance from specified datum ARP is&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},"categories":[345],"tags":[],"_links":{"self":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14464"}],"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=14464"}],"version-history":[{"count":0,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14464\/revisions"}],"wp:attachment":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/media?parent=14464"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/categories?post=14464"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/tags?post=14464"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}