[{"data":1,"prerenderedAt":333},["ShallowReactive",2],{"learn-\u002Flearn\u002Faircraft-icing-explained":3,"learn-nav-\u002Flearn\u002Faircraft-icing-explained":304},{"id":4,"title":5,"body":6,"date":243,"description":244,"draft":245,"extension":246,"faqs":247,"howTo":257,"keyTakeaways":257,"meta":258,"navigation":259,"path":260,"quiz":261,"seo":289,"series":257,"seriesOrder":257,"sources":290,"stem":301,"topic":302,"__hash__":303},"learn\u002Flearn\u002Faircraft-icing-explained.md","Aircraft icing explained",{"type":7,"value":8,"toc":233},"minimark",[9,13,19,24,54,57,61,75,97,100,104,116,137,141,170,184,188,214,218],[10,11,12],"p",{},"Ice on an aircraft is not just extra weight; it changes the shape of the wing, and a wing that has lost its shape has lost lift it may badly need.",[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},"what-airframe-icing-is","What airframe icing is",[10,25,26,27,31,32,35,36,39,40,47,48,53],{},"Structural, or airframe, icing forms when an aircraft flies through ",[28,29,30],"strong",{},"supercooled liquid water",": water droplets that are still liquid even though their temperature is below freezing. When the aircraft strikes them, they freeze onto the leading edges, the windscreen, the antennas, and any other exposed surface. The two ingredients are simple and must occur together: ",[28,33,34],{},"visible moisture"," (cloud, rain, or drizzle) and an ",[28,37,38],{},"airframe at or below 0 degrees C",". The ",[41,42,46],"a",{"href":43,"rel":44},"https:\u002F\u002Fwww.faa.gov\u002FdocumentLibrary\u002Fmedia\u002FAdvisory_Circular\u002FAC_91-74B.pdf",[45],"nofollow","FAA's pilot guide to flight in icing conditions (AC 91-74B)"," sets out these conditions, and the ",[41,49,52],{"href":50,"rel":51},"https:\u002F\u002Fwww.faa.gov\u002Fregulationspolicies\u002Fhandbooksmanuals\u002Faviation\u002Ffaa-h-8083-28b-aviation-weather-handbook",[45],"FAA Aviation Weather Handbook (FAA-H-8083-28)"," covers the meteorology behind them.",[10,55,56],{},"Ice harms the aircraft in several ways at once: it adds weight, it spoils the airflow over the wing and tail so they stall at a lower angle of attack, it increases drag, and it can jam control surfaces or block the pitot and static system that feeds your instruments. The shape change matters more than the weight.",[20,58,60],{"id":59},"the-three-types-of-ice","The three types of ice",[10,62,63,64,68,69,74],{},"The kind of ice you get depends mainly on droplet size and temperature, and the ",[41,65,67],{"href":43,"rel":66},[45],"FAA"," and ",[41,70,73],{"href":71,"rel":72},"https:\u002F\u002Fwww1.grc.nasa.gov\u002Faeronautics\u002Ficing\u002F",[45],"NASA's icing research"," describe three families:",[76,77,78,85,91],"ul",{},[79,80,81,84],"li",{},[28,82,83],{},"Rime ice"," comes from small droplets that freeze almost the instant they hit the surface. The trapped air gives a rough, brittle, opaque, milky deposit, usually building forward into the airflow. It tends to form in colder cloud.",[79,86,87,90],{},[28,88,89],{},"Clear ice"," (also called glaze) comes from larger droplets that do not freeze on contact but flow back across the surface before freezing. The result is a smooth, hard, glassy, and much heavier layer that is difficult to see and harder to shed. It tends to form in warmer cloud and in freezing rain.",[79,92,93,96],{},[28,94,95],{},"Mixed ice"," is a combination of the two, with the roughness of rime and the density of clear ice.",[10,98,99],{},"As a rule, colder air and smaller droplets favour rime, while warmer air and larger droplets favour clear ice; the two shade into one another rather than switching at a single temperature.",[20,101,103],{"id":102},"where-ice-lives-and-supercooled-large-droplets","Where ice lives, and supercooled large droplets",[10,105,106,107,110,111,115],{},"Supercooled water exists across a wide band. Most airframe icing occurs roughly between ",[28,108,109],{},"0 and minus 20 degrees C",", although supercooled droplets can persist to around minus 40 degrees C, as the ",[41,112,114],{"href":50,"rel":113},[45],"FAA Aviation Weather Handbook"," describes. Below that, cloud is usually made of ice crystals, which generally do not stick to a cold airframe.",[10,117,118,119,128,129,132,133,136],{},"The worst case is ",[28,120,121,127],{},[41,122,126],{"href":123,"className":124},"\u002Flearn\u002Fglossary#gt-supercooled-large-droplets",[125],"glossary-link","supercooled large droplets"," (SLD)",", the size of freezing drizzle or freezing rain. These are large enough to run back past the leading edges that a de-icing or anti-icing system protects and then freeze, building ",[28,130,131],{},"ridges of ice on unprotected surfaces"," behind the boots. Many aircraft are certified only for the smaller-droplet icing envelope and not for SLD, which is why the ",[41,134,67],{"href":43,"rel":135},[45]," treats freezing rain and freezing drizzle as a distinct and serious hazard, and why certification rules define separate icing envelopes for them.",[20,138,140],{"id":139},"the-forecast-and-what-each-authority-expects","The forecast, and what each authority expects",[10,142,143,144,149,150,154,155,149,160,163,164,169],{},"Icing is forecast and warned about in the products you already brief. A ",[41,145,148],{"href":146,"className":147},"\u002Flearn\u002Fglossary#gt-sigmet",[125],"SIGMET"," uses ",[151,152,153],"code",{},"SEV ICE"," for severe icing, an ",[41,156,159],{"href":157,"className":158},"\u002Flearn\u002Fglossary#gt-airmet",[125],"AIRMET",[151,161,162],{},"MOD ICE"," for moderate icing, and TAFs, area forecasts, and significant-weather charts carry the icing picture, all under the meteorological framework of ",[41,165,168],{"href":166,"rel":167},"https:\u002F\u002Fstore.icao.int\u002Fen\u002Fannex-3-meteorological-service-for-international-air-navigation-1",[45],"ICAO Annex 3",".",[10,171,172,173,177,178,183],{},"The rules on flying into it differ by authority and by aircraft, so this is where to be precise. In the United States the ",[41,174,176],{"href":43,"rel":175},[45],"FAA's AC 91-74B"," frames flight in icing around whether the aircraft is approved for flight into known icing and around avoiding conditions beyond its certification. In the United Kingdom the ",[41,179,182],{"href":180,"rel":181},"https:\u002F\u002Fwww.caa.co.uk\u002Fgeneral-aviation\u002Fsafety-topics\u002Fsafety-sense-leaflets\u002F",[45],"UK CAA's Safety Sense leaflets"," give equivalent guidance for general aviation, including the handling of airframe icing and the limits of light aircraft. The common thread is that an aircraft without ice-protection equipment, or one outside its approved envelope, must avoid icing conditions rather than fly through them.",[20,185,187],{"id":186},"common-pitfalls","Common pitfalls",[76,189,190,196,202,208],{},[79,191,192,195],{},[28,193,194],{},"Clear ice is hard to see,"," especially at night or on a wet windscreen, yet it is the heavy, fast-building kind. Do not wait until you can see it clearly.",[79,197,198,201],{},[28,199,200],{},"Tailplane icing can bite first."," The tailplane is often a smaller, sharper aerofoil that collects ice faster than the wing, and tailplane stall behaves differently from a wing stall.",[79,203,204,207],{},[28,205,206],{},"Freezing rain and freezing drizzle are a trap,"," because the droplets are large and may exceed what the aircraft is certified to handle.",[79,209,210,213],{},[28,211,212],{},"Carburettor and induction icing are separate problems"," that can occur even in air well above freezing on a humid day, so they are not covered by an airframe-icing forecast alone.",[20,215,217],{"id":216},"in-pilot-efb","In Pilot EFB",[10,219,220,221,224,225,228,229,232],{},"Pilot EFB pulls the weather for your route and shows the ",[28,222,223],{},"decoded"," report alongside the ",[28,226,227],{},"raw"," text, so the SIGMETs, AIRMETs, and forecasts that warn of icing are in front of you in plain language with the original code preserved. It does ",[28,230,231],{},"not"," predict whether your particular aircraft will pick up ice, and it is not a certified Electronic Flight Bag. Treat it as a study and planning aid: judge icing against your aircraft's approved limitations, its ice-protection equipment, and your official meteorological source. Saved weather stays readable offline; pulling a fresh forecast needs a connection.",{"title":234,"searchDepth":235,"depth":235,"links":236},"",2,[237,238,239,240,241,242],{"id":22,"depth":235,"text":23},{"id":59,"depth":235,"text":60},{"id":102,"depth":235,"text":103},{"id":139,"depth":235,"text":140},{"id":186,"depth":235,"text":187},{"id":216,"depth":235,"text":217},"2026-06-09","How airframe ice forms, the difference between rime, clear and mixed ice, what makes supercooled large droplets so dangerous, and where to find the icing forecast.",false,"md",[248,251,254],{"q":249,"a":250},"What conditions are needed for airframe icing?","Structural icing needs two things at once: visible moisture, such as cloud, rain or drizzle, and an airframe at or below 0 degrees C. The water in the cloud is supercooled, meaning it is still liquid below freezing, and it turns to ice when the aircraft strikes it. The FAA's pilot guide to flight in icing conditions sets out these basics.",{"q":252,"a":253},"What is the difference between rime, clear and mixed ice?","Rime ice forms from small droplets that freeze almost instantly, trapping air to give a rough, opaque, milky deposit, and tends to occur in colder cloud. Clear ice forms from larger droplets that flow back over the surface before freezing, giving a smooth, hard, glassy and heavier layer that is harder to see, and tends to occur in warmer cloud. Mixed ice is a combination of the two.",{"q":255,"a":256},"Why are supercooled large droplets so dangerous?","Supercooled large droplets, the size of freezing drizzle or freezing rain, can run back behind the areas a de-icing or anti-icing system protects and freeze there, forming ridges of ice on unprotected surfaces. Many aircraft are not certified for these conditions, which is why freezing rain and freezing drizzle are treated as a serious hazard by the FAA.",null,{},true,"\u002Flearn\u002Faircraft-icing-explained",[262,271,280],{"q":263,"options":264,"answer":269,"explanation":270},"Which two ingredients must occur together for structural airframe icing to form?",[265,266,267,268],"Clear skies and an airframe below freezing","Visible moisture and an airframe at or below 0 degrees C","High humidity and an air temperature above freezing","Ice crystals and a warm airframe",1,"Structural icing needs visible moisture, such as cloud, rain, or drizzle, together with an airframe at or below 0 degrees C. The supercooled water freezes onto the aircraft when it strikes them.",{"q":272,"options":273,"answer":278,"explanation":279},"Compared with rime ice, clear ice tends to be:",[274,275,276,277],"Smooth, hard, glassy, heavier, and harder to see","Rough, brittle, opaque, and milky","Made of ice crystals that do not stick","Lighter and easier to shed than rime",0,"Clear ice comes from larger droplets that flow back across the surface before freezing, giving a smooth, hard, glassy, and much heavier layer that is difficult to see and harder to shed. Rime is the rough, brittle, opaque, milky deposit.",{"q":281,"options":282,"answer":287,"explanation":288},"Across roughly what temperature band does most airframe icing occur?",[283,284,285,286],"Between 0 and minus 40 degrees C","Below minus 40 degrees C","Above 0 degrees C on humid days","Roughly between 0 and minus 20 degrees C",3,"Most airframe icing occurs roughly between 0 and minus 20 degrees C, though supercooled droplets can persist to around minus 40 degrees C. Below that, cloud is usually ice crystals, which generally do not stick to a cold airframe.",{"title":5,"description":244},[291,293,295,297,299],{"label":292,"url":166},"ICAO Annex 3: Meteorological Service for International Air Navigation",{"label":294,"url":43},"FAA Advisory Circular 91-74B: Pilot Guide, Flight in Icing Conditions",{"label":296,"url":50},"FAA Aviation Weather Handbook (FAA-H-8083-28B)",{"label":298,"url":180},"UK CAA Safety Sense leaflets",{"label":300,"url":71},"NASA Glenn Research Center: aircraft icing","learn\u002Faircraft-icing-explained","Weather","-7QhKm1gDJkR22Eqhip62K8PYUHv20NpuiwFL136uZM",{"related":305,"newer":323,"older":328,"series":257},[306,311,315],{"path":307,"title":308,"description":309,"date":310,"topic":302,"draft":245,"minutes":287,"series":257,"seriesOrder":257},"\u002Flearn\u002Freading-a-surface-analysis-chart","How to read a surface analysis chart","Decode a surface analysis chart: isobars and the pressure gradient, highs and lows, warm, cold and occluded fronts, and what the big picture tells you before you read the METAR.","2026-06-20",{"path":312,"title":313,"description":314,"date":310,"topic":302,"draft":245,"minutes":287,"series":257,"seriesOrder":257},"\u002Flearn\u002Fthe-international-standard-atmosphere","The International Standard Atmosphere (ISA)","What the ICAO International Standard Atmosphere is, its sea-level values and lapse rate, and how ISA deviation underpins altimetry, performance and density altitude.",{"path":316,"title":317,"description":318,"date":319,"topic":302,"draft":245,"minutes":320,"series":321,"seriesOrder":322},"\u002Flearn\u002Fhow-to-read-a-sigmet-and-airmet","How to read a SIGMET and an AIRMET","What SIGMETs and AIRMETs warn of, the phenomena codes, how long each stays valid, and a worked SIGMET decoded field by field, with the ICAO baseline and the US differences.","2026-06-18",5,"decode-the-weather",4,{"path":324,"title":325,"description":326,"date":327,"topic":302,"draft":245,"minutes":322,"series":257,"seriesOrder":257},"\u002Flearn\u002Fdensity-altitude-and-aircraft-performance","Density altitude and aircraft performance","What density altitude is, how to estimate it from pressure altitude and temperature, and why high, hot and humid conditions quietly rob an aircraft of performance.","2026-06-10",{"path":329,"title":330,"description":331,"date":332,"topic":302,"draft":245,"minutes":320,"series":257,"seriesOrder":257},"\u002Flearn\u002Faltimetry-qnh-qfe-qne","Altimetry: QNH, QFE and the standard setting","What QNH, QFE and the standard pressure setting actually do to your altimeter, the difference between transition altitude and transition level, and the EASA and FAA conventions that differ.","2026-06-08",1781989193098]