{"id":14456,"date":"2025-06-07T16:12:59","date_gmt":"2025-06-07T10:42:59","guid":{"rendered":"https:\/\/ibexaviation.com\/pilot-training\/?p=14456"},"modified":"2026-07-26T10:23:50","modified_gmt":"2026-07-26T04:53:50","slug":"temperature-measurement","status":"publish","type":"post","link":"https:\/\/ibexaviation.com\/pilot-training\/temperature-measurement\/","title":{"rendered":"Temperature Measurement"},"content":{"rendered":"<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-1.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<h2>Measurement of Temperature in Aviation<\/h2>\n<p>Outside Air Temperature (OAT) is measured to calculate accurate airspeed, aircraft performance, and engine efficiency. It also helps pilots detect icing conditions and plan safe flight operations.<\/p>\n<h3>Importance of Outside Air Temperature Measurement in Aviation<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-2.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Outside Air Temperature (OAT) affects air density, which in turn affects:\n<ul>\n<li>Aircraft performance<\/li>\n<li>Engine power<\/li>\n<li>Measurement of speed and altitude<\/li>\n<\/ul>\n<\/li>\n<li>Temperature measurement is required to avoid icing conditions.<\/li>\n<\/ul>\n<h3>Flight Safety Hazards of Aircraft Icing<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-3.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<p>Aircraft icing is a serious hazard to flight safety. Aircraft Icing may result in:<\/p>\n<ul>\n<li>Loss of lift.<\/li>\n<li>Increase in weight and drag.<\/li>\n<li>Freezing and loss of flight controls.<\/li>\n<li>Reduced engine power.<\/li>\n<li>Engine flameout.<\/li>\n<li>Airframe damage.<\/li>\n<\/ul>\n<h2>Types of Thermometers<\/h2>\n<h3>Direct Reading Thermometer<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-4.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Mounted on the wind-shield of low-speed aircraft.<\/li>\n<li>Measures temperature by unequal expansion of a bi-metallic strip.<\/li>\n<li>Typically uses Invar and Brass in the bi-metallic strip.<\/li>\n<li>The strip bends toward the metal having the lower coefficient of expansion.<\/li>\n<li>Unsuitable at higher speeds due to adiabatic heating.<\/li>\n<li>Adiabatic heating is caused by the high-speed movement of the aircraft through the air.<\/li>\n<\/ul>\n<h3>Remote Indicating Thermometer<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-5.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Measures temperature by the change in electrical resistance.<\/li>\n<li>Uses a Wheatstone Bridge circuit.<\/li>\n<li>One part of the circuit is exposed to outside air while the other remains inside.<\/li>\n<li>Measures current flow caused by resistance imbalance.<\/li>\n<li>Provides temperature information in electrical form.<\/li>\n<li>Information can be transmitted to other instruments and aircraft systems.<\/li>\n<\/ul>\n<h2>Total Air Temperature (TAT) Probe<\/h2>\n<h3>Design of Total Air Temperature (TAT) Probe<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-6.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The TAT probe is used in Remote Indicating Thermometers.<\/li>\n<li>The probe is located on the forward fuselage to minimise the boundary layer effect.<\/li>\n<li>Uses platinum sensors for high conductivity and rapid response.<\/li>\n<li>Housed in an air intake made of nickel-plated beryllium copper.<\/li>\n<li>Provides strength and excellent thermal conductivity.<\/li>\n<\/ul>\n<h3>Construction of Total Air Temperature Probe<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-7.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Air is directed to strike the probe at right angles to the airflow.<\/li>\n<li>Removes solid particles, water droplets, and high-pressure air.<\/li>\n<li>Includes a heating element to prevent icing.<\/li>\n<li>Heating error is normally less than 1\u00b0C and is adjusted during calibration.<\/li>\n<\/ul>\n<h3>Design of Aspirated Total Air Temperature Probe<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-8.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Stationary aircraft may contain stagnant pre-heated air inside the housing.<\/li>\n<li>This results in incorrect ground temperature indication.<\/li>\n<li>An aspirator circulates air from the engine to remove stagnant air.<\/li>\n<li>An aspirated TAT probe provides accurate ground temperature measurements.<\/li>\n<\/ul>\n<h2>Errors in Temperature Measurement<\/h2>\n<h3>Instrument and Environmental Errors in TAT Probe<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-9.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Instrument errors are caused by manufacturing imperfections.<\/li>\n<li>Reduced through improved manufacturing techniques.<\/li>\n<li>Environmental errors result from external conditions.<\/li>\n<li>Solar heating causes temperature measurement errors.<\/li>\n<li>Reduced by shielding the probe.<\/li>\n<li>Ice accretion causes additional errors.<\/li>\n<li>Reduced by using heating elements.<\/li>\n<\/ul>\n<h3>Heating Errors in Temperature Measurement<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-10.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Heating errors occur because of aircraft movement through the air.<\/li>\n<li>They indicate temperatures higher than the actual ambient temperature.<\/li>\n<li>Heating errors increase as aircraft speed increases.<\/li>\n<\/ul>\n<h3>Kinetic Heating Errors in Temperature Measurement<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-11.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Kinetic heating is caused by friction.<\/li>\n<li>More air molecules strike the probe every second at higher speeds.<\/li>\n<li>Error is greatest in direct-reading temperature probes.<\/li>\n<\/ul>\n<h3>Adiabatic Heating Errors in Temperature Measurement<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-12.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Adiabatic heating results from compression of air.<\/li>\n<li>Occurs when moving air is rapidly brought to rest.<\/li>\n<li>Error is greatest in remote-indicating temperature probes.<\/li>\n<\/ul>\n<h2>SAT &#8211; TAT &#8211; RAT<\/h2>\n<h3>Static Air Temperature (SAT)<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-13.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>SAT is the actual temperature of undisturbed air outside the aircraft.<\/li>\n<li>The objective is to measure this temperature accurately.<\/li>\n<li>SAT is obtained by correcting TAT probe errors.<\/li>\n<li>Also known as Corrected Outside Air Temperature (COAT).<\/li>\n<\/ul>\n<h3>Total Air Temperature (TAT)<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-14.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>TAT is the temperature attained when air is brought to rest by the probe.<\/li>\n<li>Total Ram Rise is the actual temperature increase due to adiabatic heating.<\/li>\n<li>TAT is always higher than SAT.<\/li>\n<li>The measured ram rise is less than the total ram rise because of system losses.<\/li>\n<\/ul>\n<h3>Ram Air Temperature (RAT)<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-15.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>RAT is the temperature indicated by the TAT probe.<\/li>\n<li>Measured Ram Rise is the increase in temperature detected by the probe.<\/li>\n<li>RAT equals SAT plus the measured ram rise.<\/li>\n<li>Also known as Indicated Outside Air Temperature (IOAT).<\/li>\n<\/ul>\n<h3>Total and Measured Ram Rise<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-16.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Total Ram Rise = Total Air Temperature (TAT) \u2212 Static Air Temperature (SAT).<\/li>\n<li>Measured Ram Rise is the ram rise indicated by the TAT probe.<\/li>\n<li>Measured Ram Rise is less than Total Ram Rise because of measurement losses.<\/li>\n<li>Measured Ram Rise = Ram Air Temperature (RAT) \u2212 Static Air Temperature (SAT).<\/li>\n<\/ul>\n<h3>Recovery Factor<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-17.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Recovery Factor is the ratio of Measured Ram Rise to Total Ram Rise.<\/li>\n<li>Measured Ram Rise = Total Ram Rise \u00d7 Recovery Factor.<\/li>\n<li>Measured Temperature = Actual Temperature + Measured Ram Rise.<\/li>\n<li>Ram Air Temperature = Static Air Temperature + Measured Ram Rise.<\/li>\n<li>IOAT = COAT + Measured Ram Rise.<\/li>\n<\/ul>\n<h3>Formula for Calculation of Static Air Temperature<\/h3>\n<ul>\n<li><strong>Rapid Formula (for use in flight):<\/strong><br \/>\n        Ram Rise = (TAS \/ 100)<sup>2<\/sup>\n    <\/li>\n<li><strong>Accurate Formula (recommended for examinations):<\/strong><br \/>\n        SAT = RAT \/ (1 + 0.2 \u00d7 Recovery Factor \u00d7 Mach Number<sup>2<\/sup>)\n    <\/li>\n<li>Recovery Factor is obtained from the Aircraft Flight Manual.<\/li>\n<\/ul>\n<h3>Units of Temperature Measurement<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-18.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The Celsius or Centigrade scale is based on the boiling point of water at 100\u00b0C.<\/li>\n<li>The Kelvin scale starts from Absolute Zero.<\/li>\n<li>Absolute Zero indicates the absence of heat energy.<\/li>\n<li>Kelvin = Celsius + 273.<\/li>\n<li>Conversion examples:\n<ul>\n<li>0\u00b0C = 273 K<\/li>\n<li>0 K = -273\u00b0C<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h3>Calculation Methods for Static Air Temperature<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-20.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Navigation Computer (recommended in examinations).<\/li>\n<li>Air Data Correction Tables for the aircraft type.<\/li>\n<li>Automatic calculation by the Air Data Computer (ADC).<\/li>\n<\/ul>\n<h2>Calculation of Static Air Temperature (Example)<\/h2>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i2-temperature-measurement-22.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<h3>Given<\/h3>\n<ul>\n<li>RAT (IOAT) = -20\u00b0C<\/li>\n<li>Mach Number = 0.73<\/li>\n<li>Recovery Factor (Kr) = 0.98<\/li>\n<\/ul>\n<h3>Solution<\/h3>\n<ul>\n<li>Convert RAT to Kelvin:<br \/>\n        253 K\n    <\/li>\n<li>\n        SAT = TAT \/ (1 + 0.2 \u00d7 Kr \u00d7 M\u00b2)\n    <\/li>\n<li>\n        SAT = 253 \/ (1 + (0.2 \u00d7 0.98 \u00d7 0.73\u00b2))\n    <\/li>\n<li>\n        SAT = 253 \/ 1.1044\n    <\/li>\n<li>\n        SAT = 229 K\n    <\/li>\n<li>\n        229 K = <strong>-44\u00b0C<\/strong>\n    <\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Measurement of Temperature in Aviation Outside Air Temperature (OAT) is measured to calculate accurate airspeed, aircraft performance, and engine efficiency. It also helps pilots detect icing conditions and plan safe flight operations. Importance of Outside Air Temperature Measurement in Aviation Outside Air Temperature (OAT) affects air density, which in turn affects: Aircraft performance Engine power Measurement of speed and altitude Temperature measurement is required to avoid icing conditions. Flight Safety Hazards of Aircraft Icing Aircraft icing is a serious hazard to flight safety. Aircraft Icing may result in: Loss of&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-14456","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\/14456","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=14456"}],"version-history":[{"count":1,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14456\/revisions"}],"predecessor-version":[{"id":16646,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14456\/revisions\/16646"}],"wp:attachment":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/media?parent=14456"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/categories?post=14456"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/tags?post=14456"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}