Icing Flashcards
When does ice form on aircraft in flight?
Ice can only form on the surface of an aircraft in flight if the temperature of the airframe is below 0°.
OR if supercooled water droplets are present.
Why would super-cooled water exist?
A lack of hygroscopic nuclei.
Why is the size of water droplets important for super-cooled water?
The smaller the droplets, the lower the temperature is that they can reach and remain in liquid form.
What are the main types of icing?
Rime Ice
Clear Ice
Hoar Frost
Rain Ice
What happens when super-cooled droplets hit an aircraft frame?
They freeze. But, when the droplets freeze, latent heat is released. This means some droplets may flow backwards over the aircraft skin and gradually freeze.
What is Rime Ice?
Small super-cooled droplets freeze so rapidly on impact that they do not spread out. Icing builds up on leading edges and trapped air creates an opaque appearance.
Occurs at very low temperatures, below -15°.
What is Clear Ice?
Large super-cooled droplets impact and spread out before freezing, creating a solid layer of clear ice.
It can build up rapidly to heavy thick ice and can have effects on aircrafts flying characteristics.
Occurs in the range 0° to -15°.
What is Rain Ice?
When rain falls through a layer that is below freezing.
Most likely to occur in the cold air ahead of an advancing warm front.
The rapid formation of clear ice is likely.
What parts of an aircraft does ice affect?
Wings and Controls
Windscreens
Propellers
Radio Antennas
Tubes and Vents
Carburettors
Jet Engines
What clouds are associated with Severe Icing?
Cumulonimbus
Nimbostratus
How does Nimbostratus cloud cause severe icing unlike other stratiform cloud?
Nimbostratus can exist in sufficiently thick layers with enough vertical air movement to produce severe icing.
Also aircraft face a high length of exposure since they may fly through the layer for some time.
What Icing occurs on the ground?
Hoar Frost
Frost
Freezing Fog (FZFG)
Freezing Rain (FZRA)
Freezing Drizzle (FZDZ)
They will all negatively effect braking action
How does Hoar Frost occur?
Hoar Frost occurs when a sub-zero surface comes into contact with moist air.
The water turns directly into ice by deposition.
When does Hoar Frost form?
Hoar Frost will form when an aircraft has been parked overnight in sub zero temperatures.
Or when an aircraft flies from sub-zero temperatures into warm moist air, such as when descending or climbing through an inversion.
How are frost and fuel related?
Frost can form on the upper/lower surfaces of a wing due to ‘cold soaked fuel’.
What is a good indication of cold soaked fuel conditions?
The presence of frost under or above the wing.
What are the significant factors that affect the amount of icing that occurs?
Temperature
Drop Size
Airframe Shape
Kinetic Heating
Concentration
What are the two types of icing protection systems?
Anti-icing
De-icing
What is Anti-Icing?
The prevention of the formation of ice. Anti-ice systems are ones that pump chemicals or hot air over vulnerable surfaces.
What is De-Icing?
The eradication of ice once it has formed. One system is a rubber boot fitted to the leading edges that can be expanded to break off ice accumulations.
What are two impacts that Icing has on ATS?
Suitable priority must be allocated to aircraft requesting level change to avoid icing.
Care must be taken to avoid delays to departures after de-icing.
What is the name of the time-period that de-icing fluid is effective for?
Hold Over Time (HOT)
