14. Icing Flashcards
Icing
In order for icing to occur, it must actually form on the aeroplane itself. This is done by what 3 methods;
[ ] Sublimation
[ ] Flying in cloud OAT warmer than the freezing point
[ ] Hoar Frost
[ ] Hail striking airframe
[ ] Supercooled liquid striking airframe
[X] Sublimation
[ ] Flying in cloud OAT warmer than the freezing point
[X] Hoar Frost
[ ] Hail striking airframe
[X] Supercooled liquid striking airframe
1
Icing
If there is no nuclei for water colder than 0℃ to form on, the water takes on a state known as what
SUPERCOOLED
- Clouds can contain supercooled liquid droplets at temperatures as log as -45℃
1
Icing
- When supercooled water drops hit an aircraft and begin to revert to their stable state i.e. turn to ice, latent heat is given off. How many calories per gram does this use
- For every degree of superooling, ____ of the water drop freezes on impact
- 80 CAL PER G
- 1/8th
2/3
Icing
“When supercooled water drops hit an aircraft and begin to revert to their stable state i.e. turn to ice, latent heat is given off, 80 calories per gram, raising the temperature of the drop. One impact with the airframe part of the drop turns to ice, whilst the remaining parts of the drop remain as water. The ice sticks to the leading edge and the remaining water runs back over the airframe, freezing as it goes, creating ice on the entire control surfaces”
This is the definition of what sort of icing
CLEAR ICE
Icing
“ice formed when droplets freeze on impact with the airframe instantaneously. Because they are at a very low temperature and very small, they trap tiny pockets of air and will form white, crunchy, easily broken and easily cleared ice”
This is the definition of what sort of icing
RIME ICE
3
Icing
- No icing occurs at temperatues above ____℃ or below ____℃
- Clear ice forms in stratus between ____℃ and ____℃
- Clear ice forms in cumulus between ____℃ and ____℃
- ABOVE 0℃ or BELOW -45℃
- 0℃ and -7℃
- 0℃ and -23℃
Icing
- The highest proportion of dangerous clear ice forms in cloud at temperatues ____℃
- The worst airframe icing occurs in CONVECTIVE or ADVECTIVE cloud,
- with COLD or WARM saturated air coming in at low level;
- with an OAT of ____℃
- JUST BELOW 0℃
- CONVECTIVE
- WARM SATURATED
- JUST BELOW 0℃
- The worst airframe icing occurs in convective cloud, with warm saturated air coming in at low level and the OAT just below 0℃
- This defines the most rapid bul up of ice as it has the highest concentration of the largest super cooled water drops i.e. if the air is warm, it contains more water vapour than when cold
- To hold super cooled water drops aloft, the clodu must actively be convective i.e. Cu, CB, Thunderstorm.
4
Icing
The zero degree isotherm is found at which heights in the following locations;
- Polar regions
- Temperate regions
- Tropics
- GROUND LEVEL
- MSL to 10,000 ft
- 14,000 to 16,000 ft
6
Icing
Complete the following diagram with the type of ice and sevrity
- Nil
- Trace
- Light
- Moderate
- Light/Moderate
- Moderate/Severe
- Rime
- Clear/Rime
- Clear
- NIL and NIL
- TRACE and RIME
- LIGHT and RIME
- LIGHT and CLEAR/RIME
- MODERATE and CLEAR/RIME
- LIGHT/MODERATE and CLEAR/RIME
- MODERATE and CLEAR/RIME
- MODERATE and CLEAR
- MODERATE/SEVERE and CLEAR
- MODERATE/SEVERE and CLEAR
- HINT;
- For icing type, ignoring the first square at top of column, Rime is all the way down apart from bottom 3, Clear ice goes all the way up apart from top 3
- For severity, thinkg of the alphabet order M, N.
- Moderate icing starts with Ns all the way down
- Severe are the last 2
- Light are the 2 surrounding the first M starting at N
7
Icing
Where will you obtained the worst airframe icing possible i.e. what temperate latitude and what cloud type
TROPICAL CB
- The -45℃ isothemr varies from 18,000ft over the arctic to 37,000ft over the equator in January, and up to 40,000ft over Northern India in July
- Tropical thunderstorms carry lots of water vapour to high altitudes
7
Icing
Distribution of supercooled water droplets and ice within a cloud varies with temperature.
- There is an INCREASE or DECREASE in the numebr of supercooled droplets with a decrease in temperature
- The size will INCREASE or DECREASE with an a decrease in altitude
- DECREASE
- INCREASE
- At atltudes where the air temperature is colder than -35℃, supercooled water droplets are rare so chances of ice formation are very small
- Icing in general is not a significant threat at altitude where air temperature is colder than -20℃ apart from large CU or CB clouds
8
Icing
Which of the following factors affect the icing threat;
[ ] Particle Size
[ ] Being over sea or land
[ ] Particle Concentration
[ ] Night or day
[ ] Shape of Aircraft Surface
[ ] Aircraft speed
[ ] Type of aircraft i.e. Boeing or Airbus
[ ] Environmental Temperature
[ ] Aircraft surface temperature
[X] Particle Size
[ ] Being over sea or land
[X] Particle Concentration
[ ] Night or day
[X] Shape of Aircraft Surface
[X] Aircraft speed
[ ] Type of aircraft i.e. Boeing or Airbus
[X] Environmental Temperature
[X] Aircraft surface temperature
- The size of droplets affects teh rate of catch
- Small droplets tend to follow the airflow and are carried around the wing
- Large droplets will strike the wing
- Small droplets if hitting the wing spread back a small amount vs large droplets
- The numebr of droplets striking the wing increases with increase airspeed
- Thin wings catch more droplets than thick wings (curvature)
8
Icing
“a form of very heavy clear icing that is encountered when the aircraft is flying above the 0℃ level in cold air, but this is below the 0℃warm level ahead of it in warmer air”
This is the definition of what sort of icing
RAIN ICE
- At the warm front moves across the land, cloud is sat on the front of air descending
- Rain that then falls from the cloud falls from cloud in the warm front into the colder air beneath it
- This immediately supercools the water as the temperature is below 0℃
- If any aircraft is flying immediately below the front, icing will quickly start to form as the droplets strike the aircraft
- This gives the highest rate of accretion to other forms of icing
9
Icing
What type of cloud does rain typically fall from in a warm front rain ice scenario
NimboStratus
(NS)
- remember Nimbo means precipitation bearing
9
Icing
If an airfield were sat in a cold sector of air with the 0℃ isotherm currently at ground level, and there was a warm front of air passing overhead, although the front at ground level were still some miles away - if it started raining, what might you expect to happen, which is hazardous to operations
RAIN ICE ON THE GROUND
- If the warm front at ground level is still not yet passed but the clouds from the warm front are sat over the airfield, which is still in the cold sector, when the rain falls from the warm air into the colder air it will supercool immediately.
- When the rain reaches the ground, it will freeze on runways and aircraft, making operations extremely hazardous
10
Icing
If a pilot is caught in the 0℃ or below temperature in cold air underneath a warm front and it started to rain, increasing the risk of rain ice, what would be the best options for the pilot to escape the scenario
- FLY HIGHER INTO WARMER AIR
- FLOW LOWER BELOW THE 0℃ LEVEL
- TURN AROUND 180°
10
Icing
“forms when an airframe is very cold, and the aircraft is moved into warm moist air. The moisture in the air will sublimate directly into ice crystals on the aircraft structure”
This is the defintion of what sort of icing
HOAR FROST
- Typically seen on the ground after prolonged flight at high altitude followed by rapid descent
- Usually located over heat sinks like main wing spars or full fuel tanks where temperature is lower
11
Icing
- Hoar frost once removed WILL or WILL NOT reform
- Active frost once removed WILL or WILL NOT reform
- WILL NO
- WILL
- Active frost is similar to hoard frost in the circumstances required, but unlike hoar frost, will reform once cleared
- Active frost can only be removed by de/anti-icing fluids
12
Icing
In order for Hoar Frost or Active Frost to take place, as well as the airframe skin being below freezing, what conditions must be in place;
[ ] OAT within 3℃ of Dew point, which is below zero
[ ] Cold front with gusty winds
[ ] Very cloudy with sleet
[ ] Cloudless sky, calm winds
[ ] Warm front bringing warm, moist air
[X] OAT within 3℃ of Dew point, which is below zero
[ ] Cold front with gusty winds
[ ] Very cloudy with sleet
[X] Cloudless sky, calm winds
[X] Warm front bringing warm, moist air
12
Icing
“Moisture in the form of precipitation or high humidty can desposit frost or ice on a cold wing, even in fairly warm environments in situations where the fuel has been exposed to a cold environment for a long time and in contact with the aircraft skin”
This is the definition of what sort of icing
COLD SOAK FUEL FROST
12
Icing
“Ice becomes perceptible. Rate of accumulation of ice is slightly greater than the rate of loss due to sublimation.”
This is the definition of what category of icing
TRACE
Icing
“The rate of accumulation may create a problem for flight in this environment for one hour. Unless encountered for one hour or more, de-icing/anti-icing equipment and/or heading or altitude change not required.”
This is the definition of what category of icing
LIGHT
Icing
“The rate of accumulation is such that even short encounters become potentially hazardous. De-icing/anti-icing required to remove/prevent accumulation or heading or attitude change required.”
This is the definition of what category of icing
MODERATE
Icing
“The rate of accumulation is such that de-icing/ anti-icing equipment fails to reduce or control the hazard. De-icing/anti-icing required, immediate heading or altitude change required.”
This is the definition of what category of icing
SEVERE
Icing
“Ice crystals at temperatures just below 0℃ will melt if compressed, and freeze again when the pressure is released. When an aircraft is flying through a snow shaower, there is a small risk of snow sticking to the aircraft as a result of this process”
This is the definition of what sort of icing hazard
PACKED SNOW
13
Icing
What is the risk of very strong convective weather such as thunderstorms, especially at tropical altitudes, in relation to icing i.e. what type of ice is associated with this sort of very high altitude level of moisture
ICE CRYSTALS aka ICE CRYSTAL ICING
(ICI)
- Strong convective weather can lift high concentrations of moisture to high altitudes where it can freeze into very small ice crystlas
- Crystals can affect an engine when flying through this weather.. Whilst crystals themselves do not stick to the airframe ambiently, they can partially melt and stick to relatively warm engine surfaces
14
Icing
Ice Crystal Icing can have what affect on engines as they partially melt and prgoress through the engine core
UNCOMMANDED THRUST REDUCTION
- this may occur because of either direct or indirect effects of the passage of ice crystals and melting through the engine core
15
Icing
“Defined as cloud ice mass in unit volume of atmsopheric air, as low as 0.0001 g/m^3 in thin cirrus to 1 g/m^3 inside a convective core”
This is the definition of what
CLOUD ICE WATER CONTENT
(IWC)
15
Icing
Which of the folowing are clues as to the presence of ice crystals at densities with potential to affect engine function;
[ ] Air temp significantly above the corresponding ISA temp
[ ] Air temp significantly below the corresponding ISA temp
[ ] Pressence of light turbulence
[ ] Pressence of severe turbulence
[ ] Light rain detected below freezing level
[ ] Heavy rain detected below freezing level
[ ] St Elmos Fire on flight deck windscreen
[ ] Moisture droplets on a heated windscreen
[ ] Clear skies in winter
[X] Air temp significantly above the corresponding ISA temp
[ ] Air temp significantly below the corresponding ISA temp
[X] Pressence of light turbulence
[ ] Pressence of severe turbulence
[ ] Light rain detected below freezing level
[X] Heavy rain detected below freezing level
[X] St Elmos Fire on flight deck windscreen
[X] Moisture droplets on a heated windscreen
[ ] Clear skies in winter
15
Icing
When particular susceptibility to ICI is known;
- Deviation is typically recommended to a marin of ____NM
- When particular engine types are identified as at risk, a distance of ____NM is typically recommended
- 20 NM
- 50 NM
15
Icing
“subsonic jet engines converge air which increases air velocity, bringing a corresponding drop in pressure and temperature. The drop in temperature takes the intake temperature down to the icing range and if humidity is high, there is a risk of ice forming”
This is the defintiion of what sort of icing
JET ENGINE INTAKE ICING
16
Icing
“commonly associated with piston engine intake engines, there is typically a form of restricted throat or venturi in the air intake where air speeds up and pressure and temperature fall. The restriction in the throat at idle engine is severe and the temperature drop significant, which can lead to icing that makes the butterfly throttle inoperable”
This is a definition of what sort of icing
CARBURETTOR ICING
17
Icing
The most significant risk of carburettor icing occurs;
- In what stages of flight
- On WARM or COLD days;
- When there is relatively HIGH or LOW humidity
- CRUSIE or DESCENT
- WARM DAYS
- HIGH HUMIDITY
Icing
Icing
Icing
Icing
Icing
Icing
Icing
Supercooled water droplets are considered to be in a STABLE or UNSTABLE state
UNSTABLE
- When they strike a surface they will start to revert back to their stable state i.e. turn to ice
1
Icing
The three most common temperature zones and associated icing types are;
- Clear Ice ____℃ to ____℃
- Mixed Clear and Rime Ice ____℃ to ____℃
- Rime Ice ____℃ to ____℃
- 0℃ to -15℃
- -10℃ to -15℃
- -10℃ to -20℃
8
