[{"data":1,"prerenderedAt":330},["ShallowReactive",2],{"learn-\u002Flearn\u002Fcold-temperature-altimeter-corrections":3,"learn-nav-\u002Flearn\u002Fcold-temperature-altimeter-corrections":314},{"id":4,"title":5,"body":6,"date":241,"description":242,"draft":243,"extension":244,"faqs":245,"howTo":255,"keyTakeaways":263,"meta":268,"navigation":269,"path":270,"quiz":271,"seo":297,"series":298,"seriesOrder":298,"sources":299,"stem":311,"topic":312,"__hash__":313},"learn\u002Flearn\u002Fcold-temperature-altimeter-corrections.md","Cold-temperature altimeter corrections",{"type":7,"value":8,"toc":231},"minimark",[9,13,19,24,42,65,69,84,101,105,116,135,145,149,160,186,189,193,220,224],[10,11,12],"p",{},"A pressure altimeter does not measure height. It measures air pressure and converts it to an altitude using a model of the atmosphere, and when the real atmosphere is much colder than that model, the number on the dial flatters you. On a freezing day near high ground, that gap between indicated and true altitude is worth understanding.",[14,15,16],"blockquote",{},[10,17,18],{},"This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.",[20,21,23],"h2",{"id":22},"why-cold-air-fools-the-altimeter","Why cold air fools the altimeter",[10,25,26,27,32,33,37,38,41],{},"A pressure altimeter is calibrated to the ",[28,29,31],"a",{"href":30},"\u002Flearn\u002Fthe-international-standard-atmosphere","standard atmosphere",": a fixed assumption about how pressure falls with height. Cold air is ",[34,35,36],"strong",{},"denser"," than standard, so pressure falls off more quickly with height, and a given pressure level sits ",[34,39,40],{},"lower"," than the instrument assumes.",[10,43,44,45,51,52,55,56,59,60,64],{},"The practical result, as the ",[28,46,50],{"href":47,"rel":48},"https:\u002F\u002Fwww.faa.gov\u002Fregulations_policies\u002Fhandbooks_manuals\u002Faviation\u002Fphak",[49],"nofollow","FAA Pilot's Handbook"," puts it, is that in colder-than-standard air the altimeter ",[34,53,54],{},"over-reads",": it shows a higher altitude than you are actually at, so your ",[34,57,58],{},"true height above the ground is less than indicated",". The classic reminder is \"from high to low, look out below\", covering both moving toward lower pressure and toward lower temperature. This is distinct from the ",[28,61,63],{"href":62},"\u002Flearn\u002Faltimetry-qnh-qfe-qne","altimeter setting"," itself, which corrects for pressure, not temperature.",[20,66,68],{"id":67},"how-large-the-error-is","How large the error is",[10,70,71,72,75,76,79,80,83],{},"The error grows with two things: how far you are ",[34,73,74],{},"above the altimeter setting source",", and how far the temperature sits ",[34,77,78],{},"below standard",". As a rule of thumb it is about ",[34,81,82],{},"4 per cent of the height above the source for every 10 degrees Celsius below standard",".",[10,85,86,87,90,91,94,95,100],{},"So at 2000 feet above the source on a day 30 degrees colder than standard, the error is roughly 3 times 4 per cent, or about ",[34,88,89],{},"12 per cent of 2000 feet, which is about 240 feet"," lower than indicated. That is small at low level on a mild day and large when you combine a cold day with a high minimum altitude over terrain. The rule of thumb is for awareness; the precise figures come from the ",[34,92,93],{},"cold-temperature correction table"," in ",[28,96,99],{"href":97,"rel":98},"https:\u002F\u002Fstore.icao.int\u002Fen\u002Fprocedures-for-air-navigation-services-pans-aircraft-operations-volume-i-flight-procedures-doc-8168",[49],"ICAO Doc 8168 (PANS-OPS)",", keyed to the reported aerodrome temperature and the height above the source.",[20,102,104],{"id":103},"when-it-matters-and-what-you-correct","When it matters, and what you correct",[10,106,107,108,111,112,115],{},"The danger case is an ",[34,109,110],{},"instrument procedure in cold conditions",", particularly in ",[34,113,114],{},"mountainous terrain",", where the minimum altitudes are there to keep you clear of high ground. If the altimeter over-reads, your true clearance is eroded just when you have least to spare.",[10,117,118,119,122,123,128,129,134],{},"The fix is to ",[34,120,121],{},"add the correction to the published minimum altitudes"," so your true height meets the minimum. As the ",[28,124,127],{"href":125,"rel":126},"https:\u002F\u002Fwww.faa.gov\u002Fair_traffic\u002Fpublications\u002Fatpubs\u002Faim_html\u002Fchap7_section_3.html",[49],"FAA AIM"," and ",[28,130,133],{"href":131,"rel":132},"https:\u002F\u002Fskybrary.aero\u002Farticles\u002Faltimeter-temperature-error-correction",[49],"SKYbrary"," describe, some States and operators require this only at or below a published temperature, and some airports are specifically designated for cold-temperature correction. When you adjust an altitude that ATC has assigned, tell the controller, so the change is understood.",[10,136,137,138,141,142,83],{},"Crucially, ",[34,139,140],{},"separation from other aircraft is not the concern",". Every altimeter on the same setting shares the same temperature error, so aircraft stay correctly separated from one another. What the cold takes away is ",[34,143,144],{},"true height above terrain and obstacles",[20,146,148],{"id":147},"a-worked-example","A worked example",[10,150,151,152,155,156,159],{},"Imagine an approach with a step-down minimum of ",[34,153,154],{},"3000 feet"," above the setting source, flown on a day ",[34,157,158],{},"20 degrees colder than standard",":",[161,162,163,170,176,183],"ul",{},[164,165,166,167,83],"li",{},"The rule of thumb is 4 per cent per 10 degrees below standard, so 20 degrees gives about ",[34,168,169],{},"8 per cent",[164,171,172,173,83],{},"Eight per cent of 3000 feet is about ",[34,174,175],{},"240 feet",[164,177,178,179,182],{},"Left uncorrected, your true height at the step-down could be roughly ",[34,180,181],{},"2760 feet",", not 3000.",[164,184,185],{},"Adding the 240-foot correction and flying 3240 indicated restores about 3000 feet of true clearance.",[10,187,188],{},"The exact correction from the State's table may differ a little, but the lesson holds: the colder it is and the higher you are above the source, the more you must add.",[20,190,192],{"id":191},"common-pitfalls","Common pitfalls",[161,194,195,201,214],{},[164,196,197,200],{},[34,198,199],{},"It is the height above the source, not your altitude, that counts."," A high field elevation with a low procedure altitude can mean a small height above the source and a small correction.",[164,202,203,206,207,213],{},[34,204,205],{},"Standard altimetry does not catch it."," Setting the correct ",[28,208,212],{"href":209,"className":210},"\u002Flearn\u002Fglossary#gt-qnh",[211],"glossary-link","QNH"," is right and necessary, but it corrects for pressure, not temperature; the cold error remains until you apply a temperature correction.",[164,215,216,219],{},[34,217,218],{},"Do not correct away separation."," Apply corrections to terrain-driven minimum altitudes per procedure, not to assigned levels at random, and coordinate any change with ATC.",[20,221,223],{"id":222},"in-pilot-efb","In Pilot EFB",[10,225,226,227,230],{},"Pilot EFB includes a ",[34,228,229],{},"cold-temperature altitude correction"," among its built-in calculators, so you can see the correction for a given height above the source and temperature with the working shown. The figures are for your own awareness and planning; Pilot EFB is offline-first and is not a certified Electronic Flight Bag, so apply your operator's and the State's published procedures and the official correction tables before you act on them.",{"title":232,"searchDepth":233,"depth":233,"links":234},"",2,[235,236,237,238,239,240],{"id":22,"depth":233,"text":23},{"id":67,"depth":233,"text":68},{"id":103,"depth":233,"text":104},{"id":147,"depth":233,"text":148},{"id":191,"depth":233,"text":192},{"id":222,"depth":233,"text":223},"2026-06-21","Why a pressure altimeter over-reads in cold air, leaving you lower than indicated, and how to correct minimum altitudes for temperature on an approach in mountainous or freezing conditions.",false,"md",[246,249,252],{"q":247,"a":248},"Why does an altimeter over-read in cold air?","A pressure altimeter is calibrated to the standard atmosphere. When the air is colder than standard it is denser, so the pressure levels the altimeter measures lie lower than the instrument assumes. The result is that the altimeter shows a higher altitude than you are actually at, so your true height above terrain is less than indicated. The old reminder is, from high to low, look out below.",{"q":250,"a":251},"How big is the cold-temperature altimeter error?","As a rule of thumb it is about 4 per cent of the height above the altimeter setting source for every 10 degrees Celsius below standard. So at 2000 feet above the source on a day 30 degrees colder than standard, the error is roughly 12 per cent of 2000, or about 240 feet lower than indicated. The official correction tables in ICAO Doc 8168 give the precise figures.",{"q":253,"a":254},"When do you apply a cold-temperature correction?","On instrument procedures in cold conditions, especially in mountainous terrain, where the error can erode terrain and obstacle clearance. You add the correction to the published minimum altitudes so your true height meets the minimum. Separation from other aircraft on the same setting is not affected, because every altimeter shares the same error; it is terrain and obstacle clearance that is at risk.",{"name":256,"steps":257},"Apply a cold-temperature altitude correction",[258,259,260,261,262],"Note the height above the altimeter setting source, which is the published altitude minus the source elevation.","Find the temperature deviation from standard, or use the reported aerodrome temperature with the correction table.","Read the correction: roughly 4 per cent of the height above the source per 10 degrees Celsius below standard, or the exact value from the table.","Add the correction to the published minimum altitude so your true height meets the minimum.","Follow your operator's and the State's procedures, and tell ATC when you adjust an assigned altitude.",[264,265,266,267],"Cold air is denser than standard, so a pressure altimeter over-reads and your true altitude is lower than indicated.","As a rule of thumb the error is about 4 per cent of the height above the setting source per 10 degrees Celsius below standard.","Corrections are added to published minimum altitudes on instrument procedures in cold conditions, especially in mountainous terrain.","Separation from other aircraft on the same setting is unaffected; the risk is to terrain and obstacle clearance.",{},true,"\u002Flearn\u002Fcold-temperature-altimeter-corrections",[272,281,289],{"q":273,"options":274,"answer":279,"explanation":280},"In air colder than standard, how does the altimeter read compared with your true altitude?",[275,276,277,278],"It under-reads, so you are higher than indicated","It over-reads, so you are lower than indicated","It reads correctly, because it is calibrated","It only errors above the transition altitude",1,"Colder than standard air is denser, so the altimeter over-reads and your true altitude is lower than indicated: from high to low, look out below.",{"q":282,"options":283,"answer":233,"explanation":288},"Roughly what is the cold-temperature error at 3000 feet above the source on a day 20 degrees colder than standard?",[284,285,286,287],"About 60 feet","About 120 feet","About 240 feet","About 600 feet","About 4 per cent per 10 degrees below standard is 8 per cent for 20 degrees; 8 per cent of 3000 feet is about 240 feet.",{"q":290,"options":291,"answer":279,"explanation":296},"Why is separation from other aircraft on the same setting not the concern in cold air?",[292,293,294,295],"Because the error is too small to matter","Because every altimeter shares the same error, so the concern is terrain and obstacle clearance","Because ATC corrects it automatically","Because separation uses GPS, not altimeters","Every altimeter on the same setting shares the same temperature error, so relative separation holds; it is true height above terrain and obstacles that is reduced.",{"title":5,"description":242},null,[300,302,304,307,309],{"label":301,"url":97},"ICAO Doc 8168: PANS-OPS, Volume I (Flight Procedures)",{"label":303,"url":125},"FAA Aeronautical Information Manual, Chapter 7 Section 3 (Cold Temperature Barometric Altimeter Errors)",{"label":305,"url":306},"FAA Instrument Procedures Handbook (FAA-H-8083-16B)","https:\u002F\u002Fwww.faa.gov\u002Fregulations_policies\u002Fhandbooks_manuals\u002Faviation\u002Finstrument_procedures_handbook",{"label":308,"url":47},"FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C)",{"label":310,"url":131},"SKYbrary: Altimeter Temperature Error Correction","learn\u002Fcold-temperature-altimeter-corrections","Operations","0qbEVU_TKiNjwBsiU6qT2FLeB-vq0G1Tbnx1Z18ofO4",{"related":315,"newer":298,"older":316,"series":298},[316,321,326],{"path":317,"title":318,"description":319,"date":241,"topic":312,"draft":243,"minutes":320,"series":298,"seriesOrder":298},"\u002Flearn\u002Fmode-s-and-ads-b-explained","Mode S and ADS-B explained","How Mode S adds a 24-bit address, selective interrogation and a data link to the transponder, the difference between elementary and enhanced surveillance, and how ADS-B broadcasts your GPS position.",4,{"path":322,"title":323,"description":324,"date":241,"topic":312,"draft":243,"minutes":325,"series":298,"seriesOrder":298},"\u002Flearn\u002Fthe-global-reporting-format-for-runway-conditions","The Global Reporting Format for runway conditions","How the Global Reporting Format (GRF) describes a contaminated runway, including the runway condition code (RWYCC) from 6 to 0, the assessment matrix (RCAM), and how the report is split into thirds.",5,{"path":327,"title":328,"description":329,"date":241,"topic":312,"draft":243,"minutes":320,"series":298,"seriesOrder":298},"\u002Flearn\u002Ftop-of-descent-and-the-3-to-1-rule","Top of descent and the 3:1 rule","How to work out your top of descent with the 3:1 rule, the 60-to-1 relationship behind it, and the rate of descent that holds a roughly 3 degree path, with a worked example.",1781989191322]