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MET Key Facts > Icing > Flashcards

Icing Flashcards

1
Q

Hazards Of Icing

A

Reduce visibility
Increase in stall speed
Reduce aerodynamic force
Restricted AC controls
Instrument errors/blocked sensor

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2
Q

Average height of freezing level

A

January - 10,000+ft in Norther latitudes/16-18,000ft around equator/16,000ft in southern hemisphere
July - 8,000ft in northern latitudes/16,18000ft around equator

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3
Q

Temp on icing key points

A

Colder temps = smaller water droplets
Higher temps = bigger water droplets

Greatest concentration of SCWD at 0 to -10 degrees
Greatest risk when airframe temp is below 0 degrees
Liquid droplets exist up to -40 degrees

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4
Q

Shape of wing on risk of icing

A

Sharper/thinner more air impact head on so greater accumulation (high aspect ratio)
More icing at higher speeds

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5
Q

Hoar Frost

A

Formed via sublimation
Clear air
Light and brittle
Common when A/C flys from cold area to warmer area with higher humidity
Cools air below dewpoint depositing hoar frost

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6
Q

Rime Ice

A

Formed from small supercooled water droplets
Found is stratiform clouds
Droplets freeze quickly trapping air
Forms at leading edges
Brittle/opaque/whitish
0 to -40 degrees

AS AC S SC NS

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7
Q

Clear Ice

A

Formed from large supercooled droplets
Very heavy/clear and dense
Typical between 0 to -15 degrees
Flow back due to delayed freezing of droplets (latent heat released slowing process of freezing on airframe)

CB TCU and dense NS

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8
Q

Freezing rain

A

Found ahead of warm fronts
Nimbo Stratus cloud
As rain falls into colder air freezes and falls onto exposed surface
Overwhelm deciding due to speed of accretion

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9
Q

Mixed Ice

A

Mixture of large and small super cooled water droplets
Rime ice and clear ice
Builds forwards and flows back
Typical between -10 and -15 degrees

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10
Q

Packed Snow

A

Forms when ice crystals or snow adhere to wet surface

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11
Q

Intake Icing

A

Accumulate around intake leading to power loss
Ice build up on fan blades degrade POF
Risk of ice ingestion

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12
Q

Ice crystal icing (New LO)

A

Associated with tropical convective systems in Asia (20-40N)
Strong updraughts create regions of high ice water content (8g/m3)

High ice water content partially melt in engine and stick/accumulate
Build up ice and loss of power

Hazards:
Does not show on radar
Occurs below -40
No airframe ice
Avoid flowing over storm cells

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13
Q

Carburettor Icing

A

Warm humid conditions
+25 degrees/30% humidity and above
Water vapour enter chamber sublimates allowing ice to form

Risk is cold/dry condition at lower power settings

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14
Q

Reporting Icing

A

Trace - no hazard + no de-icing
Light - de icing working fine (1+ hour)

Mandatory reporting to ATC
Moderate - Use of de-icing equipment and potential for diversion
Severe - De-icing not enough diversion needed

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15
Q

Orographic Intensification of icing

A

Water droplets from lower levels drawn to higher colder levels due to terrain
Increase risk of icing in cloud

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16
Q

Icing Levels Risk

A

0 to 6,500ft - Mod/severe rime/clear ice (Nimbostratus) + Light to moderate rime icing from stratuscumulus
6,500ft to 23,000ft - light to moderate rime ice
23,000ft to 40,000ft - Mainly ice crystal icing or light icing

CBS give severe clear ice conditions

17
Q

Type of cloud with greater ratio of super cooled water droplets to ice crystals

A

Stratus

18
Q

Clear ice is dangerous because

A

Is heavy and is difficult to remove from surfaces

19
Q

Icing is most likely to occur

A

-7 degree to 21 degrees and relative humidity above 80%

20
Q

Nimbostratus icing risk

A

Mod/Severe rime/clear ice

21
Q

Stratocumulus Icing Risk

A

Light to moderate

22
Q

Where do snow grains fall from

A

Mainly stratus or from fog

23
Q

Ice Water Content is

A

The ice mass per unit volume of air

24
Q

0 to -15

A

Both large and small supercooled droplets

Mostly water droplets not many ice crystals

25
Q

-15 to -40 degrees

A

Typically only small super cooled droplets

Supercooled water droplets and some ice crystals

26
Q

Below -40 degrees

A

No water droplets just ice crystals

MET Key Facts (25 decks)

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