Ch 13 (1)

Ch 13 - IcingCh 13 - Icing


• IntroductionIntroduction– Aircraft icing can have serious negative Aircraft icing can have serious negative

effects on both the powerplant and the effects on both the powerplant and the aerodynamic performance of your aerodynamic performance of your aircraftaircraft

– As a pilot, your life and the lives of your As a pilot, your life and the lives of your passengers depend on your ability to passengers depend on your ability to understand icing and to take the proper understand icing and to take the proper preflight and inflight steps to deal with it preflight and inflight steps to deal with it safelysafely


• In this chapter, you will learn to identify In this chapter, you will learn to identify and report the various types of icing, and report the various types of icing, understand its causes, and become understand its causes, and become familiar with the meteorological conditions familiar with the meteorological conditions under which it is most likely to occurunder which it is most likely to occur

• When you complete this chapter, you When you complete this chapter, you should have a basic understanding of the should have a basic understanding of the icing threat and the knowledge of how to icing threat and the knowledge of how to avoid it or at least minimize the problemavoid it or at least minimize the problem


• Section A – Aircraft Icing HazardsSection A – Aircraft Icing Hazards– Induction IcingInduction Icing– Structural IcingStructural Icing

•Ground IcingGround Icing

• Section B – Observing and Reporting Structural Section B – Observing and Reporting Structural IcingIcing– Observations of Icing Type and SeverityObservations of Icing Type and Severity– Icing PIREPsIcing PIREPs


• Section C – Microscale Icing ProcessesSection C – Microscale Icing Processes– TemperatureTemperature– Liquid Water ContentLiquid Water Content– Droplet SizeDroplet Size

• Section D – Icing and Macroscale Weather Section D – Icing and Macroscale Weather PatternsPatterns– CyclonesCyclones– Influence of MountainsInfluence of Mountains– Icing ClimatologyIcing Climatology

• Section E – Minimizing Icing EncountersSection E – Minimizing Icing Encounters


• Section A: Aircraft Icing HazardsSection A: Aircraft Icing Hazards– Icing – Icing – refers to any deposit or coating of ice refers to any deposit or coating of ice

on an aircraft. on an aircraft.

•Two types of icing are critical in the Two types of icing are critical in the operation of aircraft: induction icing and operation of aircraft: induction icing and structural icing.structural icing.


• Induction IcingInduction Icing– Induction icing – Induction icing – a general term which appliesa general term which applies

to all icing that affects the power plant operation. to all icing that affects the power plant operation. •The main effect of induction icing is power loss The main effect of induction icing is power loss

due to ice blocking the air before it enters the due to ice blocking the air before it enters the engine, thereby interfering with the fuel/air engine, thereby interfering with the fuel/air mixture.mixture.

• Induction icing includes carburetor icing and Induction icing includes carburetor icing and icing on air intakes such as screens and air icing on air intakes such as screens and air scoops.scoops.

• Carburetor icing – Carburetor icing – occurs when moist air drawn occurs when moist air drawn into the carburetor is cooled to a temperature less into the carburetor is cooled to a temperature less than 0 degrees Celsius by adiabatic expansion and than 0 degrees Celsius by adiabatic expansion and fuel vaporization.fuel vaporization.


• Structural icingStructural icing– Structural icing – Structural icing – Airframe or structural icing Airframe or structural icing

refers to the accumulation of ice on the refers to the accumulation of ice on the exterior of the aircraft during flight through exterior of the aircraft during flight through clouds or liquid precipitation when the skin clouds or liquid precipitation when the skin temperature of the aircraft is equal to, or less temperature of the aircraft is equal to, or less than 0 degrees Celsius. than 0 degrees Celsius. •The primary concern over even the slightest The primary concern over even the slightest

amount of structural icing is the loss of amount of structural icing is the loss of aerodynamic efficiency via an increase in aerodynamic efficiency via an increase in drag and a decrease in lift. drag and a decrease in lift.


– Ground icing – Ground icing – Another important form Another important form of structural icing to be considered is that of structural icing to be considered is that which may occur prior to take off. which may occur prior to take off.

An aircraft that is ice-free is as critical An aircraft that is ice-free is as critical for takeoff as it is in other phases of for takeoff as it is in other phases of flight, if not more so. flight, if not more so.

Causes of ground icing include Causes of ground icing include freezing rain, freezing drizzle and wet freezing rain, freezing drizzle and wet snow. snow.

Also, frost can be a significant hazard.Also, frost can be a significant hazard.


• ***Test data indicate that ice, snow, or frost ***Test data indicate that ice, snow, or frost having a thickness and roughness similar to having a thickness and roughness similar to medium or coarse sandpaper on the leading medium or coarse sandpaper on the leading edge and upper surface of a wing can edge and upper surface of a wing can reduce lift by as much as 30 percent and reduce lift by as much as 30 percent and increase drag by 40 percentincrease drag by 40 percent


• ***A hard frost can increase the stalling ***A hard frost can increase the stalling speed by as much as 5 or 10 percent. speed by as much as 5 or 10 percent. – An aircraft carrying a coating of frost is An aircraft carrying a coating of frost is

particularly vulnerable at low levels if it particularly vulnerable at low levels if it also experiences turbulence or wind also experiences turbulence or wind shear, especially at slow speeds and in shear, especially at slow speeds and in turns. turns.

– Frost may prevent an airplane from Frost may prevent an airplane from becoming airborne at normal takeoff becoming airborne at normal takeoff speedspeed


• Section B: Observing and Reporting Section B: Observing and Reporting Structural IcingStructural Icing– Observations of Icing Type and Severity Observations of Icing Type and Severity

•Rime ice – Rime ice – Structural icing occurs when Structural icing occurs when super cooled cloud or precipitation droplets super cooled cloud or precipitation droplets freeze on contact with an aircraft. freeze on contact with an aircraft.

– The freezing process produces three different The freezing process produces three different icing types: clear, rime, and mixed ice. icing types: clear, rime, and mixed ice.


– Rime ice is the most common icing type. Rime ice is the most common icing type.

• It forms when water droplets freeze on It forms when water droplets freeze on impact, trapping air bubbles in the ice. impact, trapping air bubbles in the ice.

– This type of ice usually forms at This type of ice usually forms at temperatures below -15 degrees Celsius.temperatures below -15 degrees Celsius.

– Rime ice appears opaque and milky white Rime ice appears opaque and milky white with a rough, porous texture. with a rough, porous texture.


– Although rime icing has serious effects on Although rime icing has serious effects on the aerodynamics of the aircraft wing, it the aerodynamics of the aircraft wing, it is regarded as the least serious type of is regarded as the least serious type of icing because it is lighter, easier to icing because it is lighter, easier to remove, and tends to form on the part of remove, and tends to form on the part of the aircraft where, if available, anti-icing the aircraft where, if available, anti-icing and/or deicing equipment is located.and/or deicing equipment is located.


•Clear ice – Clear ice – forms when droplets impacting forms when droplets impacting an airplane freeze slowly, spreading over the an airplane freeze slowly, spreading over the aircraft components. aircraft components.

– Air temperatures are usually between 0 degrees Air temperatures are usually between 0 degrees Celsius and – 5 degrees Celsius. Celsius and – 5 degrees Celsius.

– These conditions create a smooth, glossy surface These conditions create a smooth, glossy surface of streaks and bumps of hard ice. of streaks and bumps of hard ice.

– Clear ice is less opaque than rime ice. Clear ice is less opaque than rime ice. – It may actually be clear but often is simply It may actually be clear but often is simply

translucent (clear ice is also called “glaze”). translucent (clear ice is also called “glaze”).


– Clear ice is the most dangerous form Clear ice is the most dangerous form of structural icing because it is of structural icing because it is heavy and hardheavy and hard

it adheres strongly to the aircraft it adheres strongly to the aircraft surfacesurface

it greatly disrupts the airflow over it greatly disrupts the airflow over the wing and it can spread beyond the wing and it can spread beyond the location of de-icing or anti-the location of de-icing or anti-icing equipment.icing equipment.


•Runback icing – Runback icing – when ice spreads beyond the when ice spreads beyond the ice protection equipment.ice protection equipment.

•Mixed ice – Mixed ice – a combination of rime and clear icea combination of rime and clear ice– forms at intermediate temperatures (about -forms at intermediate temperatures (about -

5 degrees Celsius to -15 degrees Celsius) 5 degrees Celsius to -15 degrees Celsius) and has characteristics of both types. and has characteristics of both types.

– The variation in liquid water content in this The variation in liquid water content in this temperature range causes an aircraft that is temperature range causes an aircraft that is flying in these conditions to collect layers of flying in these conditions to collect layers of both less opaque (clear) and more opaque both less opaque (clear) and more opaque (rime) ice.(rime) ice.


• Icing intensity – Icing intensity – The severity of icing is The severity of icing is determined by its operational effect on the determined by its operational effect on the aircraft. aircraft. – Icing intensity is classified as trace, light, Icing intensity is classified as trace, light,

moderate and severe and is related to moderate and severe and is related to

•rate of accumulation of ice on the aircraftrate of accumulation of ice on the aircraft

•the effectiveness of available de-icing/anti-the effectiveness of available de-icing/anti-icing equipmenticing equipment

•and the actions you must take to combat the and the actions you must take to combat the accumulation of ice.accumulation of ice.


• Icing PIREPsIcing PIREPs– Icing PIREPs – Icing PIREPs – Pilot reports of structural icing are Pilot reports of structural icing are

often the only direct observations of that hazard often the only direct observations of that hazard and, as such, are of extreme importance to all and, as such, are of extreme importance to all pilots and aviation forecasters. pilots and aviation forecasters.

– The critical information that an icing PIREP should The critical information that an icing PIREP should contain includes location, time, flight level, aircraft contain includes location, time, flight level, aircraft type, temperature, icing intensity, and icing type. type, temperature, icing intensity, and icing type.

– Excellent aids to pilots in the diagnosis of icing Excellent aids to pilots in the diagnosis of icing conditions are graphical presentations of recent conditions are graphical presentations of recent icing PIREPs from the Aviation Digital Data Service icing PIREPs from the Aviation Digital Data Service (ADDS).(ADDS).


• Section C: Micro scale Icing Processes – Section C: Micro scale Icing Processes – icing occurrence, type, and severity depend on icing occurrence, type, and severity depend on three basic parameters: three basic parameters: – TemperatureTemperature– Liquid water content Liquid water content – Droplet sizeDroplet size


– Temperature – Temperature – icing types and critical outside icing types and critical outside air temperatures include air temperatures include

•Clear (0 to -5 degrees CelsiusClear (0 to -5 degrees Celsius

•Clear or mixed (-5 to -10 degrees Celsius)Clear or mixed (-5 to -10 degrees Celsius)

•Mixed or rime (-10 to -15 degrees Celsius)Mixed or rime (-10 to -15 degrees Celsius)

•Rime (-15 to -20 degrees Celsius)Rime (-15 to -20 degrees Celsius)


– Liquid Water Content (LWC) – Liquid Water Content (LWC) – simply a simply a measure of the liquid water due to all the measure of the liquid water due to all the super cooled droplets in that portion of the super cooled droplets in that portion of the cloud where your aircraft happens to becloud where your aircraft happens to be


– Droplet SizeDroplet Size

•Super-cooled large droplets (SLD) – Super-cooled large droplets (SLD) – associatedassociated with heavy icing and especially with heavy icing and especially with runback icing problemswith runback icing problems

•Collision/coalescence – Collision/coalescence – small water small water droplets can grow into large super cooled droplets can grow into large super cooled dropletsdroplets

– through this process, water droplets are through this process, water droplets are super cooled and they initially formed in super cooled and they initially formed in subfreezing surroundings subfreezing surroundings


• Warm layer process - Warm layer process - small water droplets can small water droplets can grow into large super cooled dropletsgrow into large super cooled droplets– through this process, when snow falls into a through this process, when snow falls into a

warm layer (temperature greater than 0 warm layer (temperature greater than 0 degrees Celsius) where ice crystals melt, and degrees Celsius) where ice crystals melt, and then fall into a cold layer (temperature less then fall into a cold layer (temperature less than 0 degrees Celsius) where the rain droplets than 0 degrees Celsius) where the rain droplets become super cooled.become super cooled.


• ***The presence of ice pellets (PL) at the ***The presence of ice pellets (PL) at the surface is evidence that there is freezing surface is evidence that there is freezing rain at a higher altituderain at a higher altitude


• Section D: Icing and Macro scale Weather Section D: Icing and Macro scale Weather PatternsPatterns– Cyclones and Fronts – Cyclones and Fronts – extra tropical extra tropical

cyclones provide a variety of mechanisms to cyclones provide a variety of mechanisms to produce widespread, upward motions. These produce widespread, upward motions. These include convergence of surface winds, frontal include convergence of surface winds, frontal lifting and convection. lifting and convection.

– Influence of Mountains – Influence of Mountains – mountainous mountainous terrain should always be considered a source terrain should always be considered a source of icing hazards when subfreezing clouds are of icing hazards when subfreezing clouds are present.present.

– Icing Climatology – Icing Climatology – refers to the average refers to the average distribution of icing for a given areadistribution of icing for a given area


• Section E: Minimizing Icing Encounters – Section E: Minimizing Icing Encounters – know know capabilities of your aircraft, decision tree capabilities of your aircraft, decision tree – Freezing level – Freezing level – analyzed on the freezing level analyzed on the freezing level

chart and appears on some aviation forecast chart and appears on some aviation forecast chartscharts

– Freezing level chart – Freezing level chart – solid lines on this chart solid lines on this chart indicate the position of particular freezing levels. indicate the position of particular freezing levels. •The dashed lines indicate where the freezing The dashed lines indicate where the freezing

level intersects the ground. level intersects the ground. •The open circles indicate the location of The open circles indicate the location of

sounding stations where freezing levels are sounding stations where freezing levels are reported in hundreds of feet MSL.reported in hundreds of feet MSL.


• SummarySummary– Icing can affect an aircraft in many Icing can affect an aircraft in many

ways, including the degradation of ways, including the degradation of aerodynamics, and causing difficulties aerodynamics, and causing difficulties with control surfaces, powerplant with control surfaces, powerplant operation, propeller balance, operation operation, propeller balance, operation of landing gear, communications, of landing gear, communications, instrument accuracy, and ground instrument accuracy, and ground handlinghandling


• SummarySummary– An icing encounter does not leave much An icing encounter does not leave much

room for errorroom for error– This is especially true when it is This is especially true when it is

combined with the additional combined with the additional complications of turbulence, wind shear, complications of turbulence, wind shear, and IMCand IMC

– In this chapter, you have learned how In this chapter, you have learned how induction and structural icing can forminduction and structural icing can form


• SummarySummary– You are now aware of the types and You are now aware of the types and

severity classifications of structural severity classifications of structural icing, and how temperature, liquid water icing, and how temperature, liquid water content, and droplet size contribute to content, and droplet size contribute to icing type and severityicing type and severity

– You now understand that the production You now understand that the production of supercooled large droplets, such as of supercooled large droplets, such as found in freezing precipitation, is of found in freezing precipitation, is of particular importance for severe icingparticular importance for severe icing


• SummarySummary- In addition, your brief examination of an - In addition, your brief examination of an

icing climatology has demonstrated how icing climatology has demonstrated how extratropical cyclones, airmasses, and extratropical cyclones, airmasses, and fronts interact with moisture sources fronts interact with moisture sources and mountains to make some and mountains to make some geographical areas more conducive to geographical areas more conducive to icing events than othersicing events than others


• SummarySummary- Finally, on the basis of icing causes and Finally, on the basis of icing causes and

characteristics, a number of practical characteristics, a number of practical rules of thumb have been established to rules of thumb have been established to help you avoid or at least minimize icing help you avoid or at least minimize icing effectseffects

- Keep in mind that these are general Keep in mind that these are general guidelines; they have not directly guidelines; they have not directly addressed the capabilities of your addressed the capabilities of your aircraft to handle icing situationsaircraft to handle icing situations


• SummarySummary- More details with regard to tools and - More details with regard to tools and

procedures for the general assessment procedures for the general assessment of all weather conditions, including icing, of all weather conditions, including icing, in the preflight phase of flight will be in the preflight phase of flight will be presented in Part IV of this textpresented in Part IV of this text

Ch 13 (1)

Business

icing runback icing

aircraft icing hazards

rime icing

carburetor icing

icing threat

icing rime ice

serious type of icing

common icing type