Ch 13 - Icing

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Ch 13 - Icing
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Ch 13 - Icing

• Introduction
• Aircraft icing can have serious negative effects
  on both the powerplant and the aerodynamic
  performance of your aircraft
• As a pilot, your life and the lives of your
  passengers depend on your ability to understand
  icing and to take the proper preflight and
  inflight steps to deal with it safely

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Ch 13 - Icing

• In this chapter, you will learn to identify and
  report the various types of icing, understand its
  causes, and become familiar with the
  meteorological conditions under which it is most
  likely to occur
• When you complete this chapter, you should have a
  basic understanding of the icing threat and the
  knowledge of how to avoid it or at least minimize
  the problem

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• Section A Aircraft Icing Hazards
• Induction Icing
• Structural Icing
• Ground Icing
• Section B Observing and Reporting Structural
  Icing
• Observations of Icing Type and Severity
• Icing PIREPs

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• Section C Microscale Icing Processes
• Temperature
• Liquid Water Content
• Droplet Size
• Section D Icing and Macroscale Weather Patterns
• Cyclones
• Influence of Mountains
• Icing Climatology
• Section E Minimizing Icing Encounters

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• Section A Aircraft Icing Hazards
• Icing refers to any deposit or coating of ice
  on an aircraft.
• Two types of icing are critical in the operation
  of aircraft induction icing and structural
  icing.

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• Induction Icing
• Induction icing a general term which applies to
  all icing that affects the power plant operation.
  
• The main effect of induction icing is power loss
  due to ice blocking the air before it enters the
  engine, thereby interfering with the fuel/air
  mixture.
• Induction icing includes carburetor icing and
  icing on air intakes such as screens and air
  scoops.
• Carburetor icing occurs when moist air drawn
  into the carburetor is cooled to a temperature
  less than 0 degrees Celsius by adiabatic
  expansion and fuel vaporization.

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• Structural icing
• Structural icing Airframe or structural icing
  refers to the accumulation of ice on the exterior
  of the aircraft during flight through clouds or
  liquid precipitation when the skin temperature of
  the aircraft is equal to, or less than 0 degrees
  Celsius.
• The primary concern over even the slightest
  amount of structural icing is the loss of
  aerodynamic efficiency via an increase in drag
  and a decrease in lift.

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• Ground icing Another important form of
  structural icing to be considered is that which
  may occur prior to take off.
• An aircraft that is ice-free is as critical for
  takeoff as it is in other phases of flight, if
  not more so.
• Causes of ground icing include freezing rain,
  freezing drizzle and wet snow.
• Also, frost can be a significant hazard.

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

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• A hard frost can increase the stalling speed
  by as much as 5 or 10 percent.
• An aircraft carrying a coating of frost is
  particularly vulnerable at low levels if it also
  experiences turbulence or wind shear, especially
  at slow speeds and in turns.
• Frost may prevent an airplane from becoming
  airborne at normal takeoff speed

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• Section B Observing and Reporting Structural
  Icing
• Observations of Icing Type and Severity
• Rime ice Structural icing occurs when super
  cooled cloud or precipitation droplets freeze on
  contact with an aircraft.
• The freezing process produces three different
  icing types clear, rime, and mixed ice.

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• Rime ice is the most common icing type.
• It forms when water droplets freeze on impact,
  trapping air bubbles in the ice.
• This type of ice usually forms at temperatures
  below -15 degrees Celsius.
• Rime ice appears opaque and milky white with a
  rough, porous texture.

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

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• Clear ice forms when droplets impacting an
  airplane freeze slowly, spreading over the
  aircraft components.
• Air temperatures are usually between 0 degrees
  Celsius and 5 degrees Celsius.
• These conditions create a smooth, glossy surface
  of streaks and bumps of hard ice.
• Clear ice is less opaque than rime ice.
• It may actually be clear but often is simply
  translucent (clear ice is also called glaze).

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• Clear ice is the most dangerous form of
  structural icing because it is heavy and hard
• it adheres strongly to the aircraft surface
• it greatly disrupts the airflow over the wing and
  it can spread beyond the location of de-icing or
  anti-icing equipment.

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• Runback icing when ice spreads beyond the ice
  protection equipment.
• Mixed ice a combination of rime and clear ice
• forms at intermediate temperatures (about -5
  degrees Celsius to -15 degrees Celsius) and has
  characteristics of both types.
• The variation in liquid water content in this
  temperature range causes an aircraft that is
  flying in these conditions to collect layers of
  both less opaque (clear) and more opaque (rime)
  ice.

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• Icing intensity The severity of icing is
  determined by its operational effect on the
  aircraft.
• Icing intensity is classified as trace, light,
  moderate and severe and is related to
• rate of accumulation of ice on the aircraft
• the effectiveness of available de-icing/anti-icing
  equipment
• and the actions you must take to combat the
  accumulation of ice.

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• Icing PIREPs
• Icing PIREPs Pilot reports of structural icing
  are often the only direct observations of that
  hazard and, as such, are of extreme importance to
  all pilots and aviation forecasters.
• The critical information that an icing PIREP
  should contain includes location, time, flight
  level, aircraft type, temperature, icing
  intensity, and icing type.
• Excellent aids to pilots in the diagnosis of
  icing conditions are graphical presentations of
  recent icing PIREPs from the Aviation Digital
  Data Service (ADDS).

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

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• Temperature icing types and critical outside
  air temperatures include
• Clear (0 to -5 degrees Celsius
• Clear or mixed (-5 to -10 degrees Celsius)
• Mixed or rime (-10 to -15 degrees Celsius)
• Rime (-15 to -20 degrees Celsius)

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

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• Droplet Size
• Super-cooled large droplets (SLD) associated
  with heavy icing and especially with runback
  icing problems
• Collision/coalescence small water droplets can
  grow into large super cooled droplets
• through this process, water droplets are super
  cooled and they initially formed in subfreezing
  surroundings

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• Warm layer process - small water droplets can
  grow into large super cooled droplets
• through this process, when snow falls into a warm
  layer (temperature greater than 0 degrees
  Celsius) where ice crystals melt, and then fall
  into a cold layer (temperature less than 0
  degrees Celsius) where the rain droplets become
  super cooled.

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

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• Section D Icing and Macro scale Weather
  Patterns
• Cyclones and Fronts extra tropical cyclones
  provide a variety of mechanisms to produce
  widespread, upward motions. These include
  convergence of surface winds, frontal lifting and
  convection.
• Influence of Mountains mountainous terrain
  should always be considered a source of icing
  hazards when subfreezing clouds are present.
• Icing Climatology refers to the average
  distribution of icing for a given area

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• Section E Minimizing Icing Encounters know
  capabilities of your aircraft, decision tree
• Freezing level analyzed on the freezing level
  chart and appears on some aviation forecast
  charts
• Freezing level chart solid lines on this chart
  indicate the position of particular freezing
  levels.
• The dashed lines indicate where the freezing
  level intersects the ground.
• The open circles indicate the location of
  sounding stations where freezing levels are
  reported in hundreds of feet MSL.

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• Summary
• Icing can affect an aircraft in many ways,
  including the degradation of aerodynamics, and
  causing difficulties with control surfaces,
  powerplant operation, propeller balance,
  operation of landing gear, communications,
  instrument accuracy, and ground handling

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• Summary
• An icing encounter does not leave much room for
  error
• This is especially true when it is combined with
  the additional complications of turbulence, wind
  shear, and IMC
• In this chapter, you have learned how induction
  and structural icing can form

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• Summary
• You are now aware of the types and severity
  classifications of structural icing, and how
  temperature, liquid water content, and droplet
  size contribute to icing type and severity
• You now understand that the production of
  supercooled large droplets, such as found in
  freezing precipitation, is of particular
  importance for severe icing

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• Summary
• - In addition, your brief examination of an icing
  climatology has demonstrated how extratropical
  cyclones, airmasses, and fronts interact with
  moisture sources and mountains to make some
  geographical areas more conducive to icing events
  than others

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• Summary
• Finally, on the basis of icing causes and
  characteristics, a number of practical rules of
  thumb have been established to help you avoid or
  at least minimize icing effects
• Keep in mind that these are general guidelines
  they have not directly addressed the capabilities
  of your aircraft to handle icing situations

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• Summary
• - More details with regard to tools and
  procedures for the general assessment of all
  weather conditions, including icing, in the
  preflight phase of flight will be presented in
  Part IV of this text