Course 5 - Section 13 - Icing Flashcards
Variables that determine how much ice an aircraft will pickup
- Speed of the aircraft
- Shape of the airfoil
- Type of cloud encountered
- Type of ice encountered
- Length of time in icing conditions
Generally, high performance aircraft collect more ice than low performance aircraft in the same amount of time because the former have thin wing profiles
List the types of icing
Hoar frost, Clear ice, Rime ice, Mixed ice
Hoar frost
Hoar frost is a greyish-white, feathery, crystalline formation that can cover the entire surface of an aircraft. it is the same as the ice that forms on cars on cold winter nights
HOAR FROST IS NOT USUALLY AN ISSUE FOR AIRCRAFT BECAUSE IT IS VERY THIN AND EASILY REMOVED
Clear ice
Clear ice is a clear, glassy, hard ice that forms on the leading edges of wings and spreads back over the wing surfaces WHEN THE AIR TEMPERATURE IS BETWEEN 0 and -10 degrees C.
This type of ice is found in freezing precipitation and in supercooled rain in clouds
Clear ice is denser and more homogenous than rime ice and is VERY DANGEROUS FOR AIRCRAFT
it can
- change the shape of the wing leading to a reducution in lift
- increase the weight of the aircraft resulting in a higher stall speed
- block the pilots view
IT IS VERY DIFFICULT TO REMOVE CLEAR ICE
Rime ice
Rime ice is an opaque, whitish, pebbly, granular type of ice that forms on the leading edges of the wings but DOES NOT SPREAD BACK OVER THE WING SURFACE
IT FORMS WHEN AIR TEMPERATURES ARE BETWEEN -15 and -20 DEGREES CELCIUS
RIME ICE ACCUMULATES MUCH MORE SLOWLY THAN CEAR ICE. the accumulation of rime ice on the leading edges of the wings can disturb the flow of air over the wings and affect lift
Rime is primarily supercooled cloud droplets and therefore CAN ONLY BE ENCOUNTERED WHILE FLYING IN CLOUDS
IT IS NOT AS DIFFICULT TO REMOVE AS CLEAR ICE
Mixed ice
Mixed ice is a mixture of clear and rime ice. it is MOST LIKELY TO FORM IN TEMPERATURES BETWEEN -10 and -15 DEGREES CELCIUS
The result is an ice coating that is WEAKER THAN CLEAR ICE BUT STRONGER THAN RIME ICE
it can
- lead to a reduction in lift
- increase the weight of the aircraft
- significantly reduce visibility
What are the icing intensities (list)
-Trace
-Light
-Moderate
-Severe
Trace icing
Light icing
Severe icing
Moderate icing
Two main conditions that produce icing
- The aircraft must be flying through visible water in the form of rain or cloud droplets
- When the water droplets strike a surface, their temperature or the temperature of the surface must be 0 degrees C or below
Supercooled water droplets
Tiny water droplets in their purest form won’t freeze right at 0 degrees C. In fact, these supercooled water droplets CAN EXIST IN A LIQUID STATE IN TEMPERATURES AS LOW AS -40 DEGREES C
However, supercooled water droplets are very unstable and, when distrubed, will rapidly change into ice
Cloud composition and icing production
While clouds composed of water droplets can form at temperatures below 0 degrees C, CLOUDS FORMED AT TEMPERATURES BELOW -20 DEGREES C ARE USUALLY COMPOSED OF ICE CYSTALES
THE HEAVIEST ICING USUALLY OCCURS FROM -10 to 0 degrees C WHEN SUPERCOOLED WATER DROPLETS FREEZE ON IMPACT AND ADHERE TO THE PLANE
Factors that contribute to the amount of icing
The amount of icing IS DIRECTLY RELATED TO THE SIZE OF THE WATER DROPLETS AND THE SIZE OF THE WATER DROPLETS IS DIRECTLY RELATED TO THE VERTICAL VELOCITIES WITHIN A CLOUD
THE FASTER THE VERTICAL MOVEMENT OF THE SUPERCOOLED DROPLETS, THE MORE COLLISIONS BETWEEN THEM AND THE LARGER THEIR SIZE
THE LARGER THE SIZE OF THE SUPERCOOLED DROPLETS, THE MORE SERIOUS THE ICING WILL BE
Icing and Cloud Types
CU, TCU and CB clouds PRODUCE THE HEAVIEST ICING POTENTIAL
In winter, STRATOCUMULUS (SC) clouds produce the MOST FREQUENT ICING CONDITIONS
THE MOST DANGEROUS TYPES OF ICING ARE ENCOUNTERED IN DENSE CLOUDS COMPOSED OF HEAVY ACCUMULATIONS OF LARGE SUPERCOOLED WATER DROPLETS AND IN FREEZING RAIN
High cirrus-type clouds are composed of ice crystals, these crystals do not adhere to aircraft
THE THICKER THE CLOUD, THE GREATER THE ICING POTENTIAL
Carburetor Icing
Carburetor icing is especially treachorous because it can form in clear air when the humidity is high and the outside air temperatures are well above freezing
The vaporization of fuel, combined with the expansion of air as it passes through the carburetor can cause a sudden cooling of the mixture
This cooling condenses the water vapour and , if the temperature in the carburetor reaches 0 degrees or below, the moisture is deposited as frost or ice inside the carburator passage
IF THE TEMPERATURE IS BETWEEN APPROX -6 to +21 degree CELCIUS, with VISIBLE MOISTURE OR HIGH HUMIDITY, carburetor ice is a very real danger
How icing affects aircraft performance (list)
- Lift is decreased (increase stall speed)
- weight is increased (increase stall speed, decrease fuel economy)
- Drag is increased (reduced rate of climb)
- Propeller efficiency is decreased (loss of power)
- Airflow to the engine is reduced (can cause complete engine failure)
- ice can reduce performance of control surfaces like elevator and rudder
How icing affects other aircraft functions (non-performance)
- clogged pitot tubes and static vents (inaccurate instruments)
- ice on windshield and canopies can cause reduced pilot visibility
- ice on radio antennas and masts may cause them to vibrate and break. ice also reduced communication efficiency
anti ice vs de-icing equipment
- anti-ice
fluids and heating devices prevent ice from forming in the first place
-de icing
rubber coverings and pneumatic systems remove ice that has already formed
The area of a cloud where heavist icing occurs
The heaviest icing usually occurs in the range from 0 to -10 degrees celcius.
However, supercooled water droplets can be found at temperatures as low is -40.
Impact of icing on NAV CANADA operations
ON THE GROUND
- There is an increased potential for aircraft icing during long delays prior to takeoff
- Icing on the runways may cause delays
- Aircraft may need to be de-iced just prior to entering the runway, delaying aircraft behind them
IN THE AIR, aircraft may
- delay descent through an icing area
- request to hold above the icing area and wait for improvement
- make a rapid climb or descent through an icing area
- request priority for approach
- request a diversion
- request a reroute to avoid the area
Reporting Icing: Pilots must include the following in icing reports
-POSITION
-TIME
-ALTITUDE
-TYPE OF AIRCRAFT
-TYPE OF ICING / INTENSITY
-WHETHER THE ICING IS EXPERIENCED IN PRECIPITATION, SUCH AS FREEZING RAIN OR SLIGHTLY WET SNOW
You must take ANY report of CLEAR ICE FORMATION seriously and pass it on to concerned parties, such as:
- The appropriate flight information centre (FIC)
- All concerned aircraft
- The unit designated for dissemination weather information, if applicable
- other concerned sectors or units if the weather is of significance
