CHAPTER 10 ICING

ICING

• Aircraft accidents generally occur after a series of events place a pilot in a box from which he cannot escape. Having knowledge of icing and how it affects your aircraft may prevent the last side of the box from closing. Ice is a Cumulative hazard

HOMEWORK

• READ CHAPTER 10

• Thursday AOPA’S Weather Wise: Precipitation and Icing is due

• Many additional free online courses can be found at the following link. Highly recommend doing the icing course it may help with Thursday’s quiz.

• https://www.faasafety.gov/login/reg/Register.aspx

SUPER-COOLED WATER DROPLETS

• When ice crystals are warmed to above freezing temperatures, they melt. On the other hand, when water droplets are cooled to below freezing they will not freeze until very cold temperatures are reached. Water droplets in this state are called “super-cooled”. If these droplets impact on an aircraft at below freezing temperatures, the jar will cause them to freeze and they will coat the aircraft with ice.

ICING ON AIRCRAFT• Ice disrupts the smooth laminar flow over

airfoils or rotors causing a decrease of lift and an increase in the stalling speed.

• Also increases the drag and weight of the aircraft.

ICING ON AIRCRAFT

• Uneven shedding of ice from propellers or rotors can cause destructive vibrations.

• Water can freeze around control surfaces and restrict their movement. Pitot heads and static vents can be blocked causing erroneous altimeter, airspeed and VSI indications

ICING ON AIRCRAFT

• Antennas can break off with resultant loss of communications and navaids.

• Ice can cover windscreens and block vision (storm window)

• Undercarriage and brakes can freeze from splach during take-off and become inoperative.

• Power can be lost from engines.

ICING ON AIRCRAFT

• Fuel consumption will increase because of increased drag and weight.

• Even the use of de-icing/anti-icing will increase the fuel consumption due to the amount of energy required to eliminate the ice.

• After time de-ice/anti-icing equipment reduce in affectiveness.

AIRFRAME ICING

• Results when super-cooled water strikes portions of the airframe that are colder than 0 degrees C. The greater the amount of super-cooled water, the worse the icing.

• The larger the liquid water content in a cloud the more severe the icing.

• In most cases you need to be flying through visible water such as rain or cloud droplets in order to have structural icing.

LIQUID WATER CONTENT

• I’ve flown a PA-31T in Argentina through a developing TCU with liquid water content so high you could see the ice forming on the leading edges of the wings. In 15 seconds we had 5 inches of ice.

• Strong vertical currents are necessary to prevent large droplets from falling out of a cloud.

LIQUID WATER CONTENT

• Strongest icing can be suspected in TS, in clouds formed by abrupt orographic lift and in lee wave clouds (mountain waves).

• In the winter environment aircraft structural icing is most likely to have the highest rate of accumulation in Thick stratified clouds producing continuous rain. Especially near the top of the clouds.

TEMPERATURE EFFECTS

• Warm air can hold more water vapour than cold air. For this reason, the amount of water droplets condensed out is greater in cloud formed in warm air masses. The warmer the cloud base suspect more severe icing.

TEMPERATURE EFFECTS

• Larger droplets begin to freeze spontaneously to ice crystals at around -10 C and as droplets get smaller, colder temps are required to freeze them. By -40 C virtually are droplets will have frozen.

• The rate of freezing increases dramatically at temperatures just below -15 C

TEMPERATURE EFFECTS

TEMPERATURE EFFECTS

• When water droplets and ice crystals exist together in a cloud, there is a tendency for the water droplets to evaporate and for the resulting water vapor to sublimate on the ice crystals. The crystals therefore, grow rapidly and begin to settle downward. As they fall, they rapidly deplete the liquid water content throughout the cloud.

TEMPERATURE EFFECTS

• When ice crystals start to form and fall from above the risk of sever icing greatly decreases.

• Icing tends to be heaviest near cloud tops unless the tops are quite cold. Heaviest near -15 to -5 C

• Expect ice between 2 to -20 C

THE FREEZING PROCESS

• The rate of freezing after impact depends on the temperature of the aircraft skin and on the air temperature

RIME CLEAR MIXED ICE

TYPES OF ICE• Three types of Ice: Rime, Clear, and Mixed

• Rime is ice which is rough, milky and opaque in appearance and is formed by the almost instantaneous freezing of small super-cooled water dropeltes. It will usually form only on the leading deges of airfoils and tends to build forward into the air-stream, forming finger and ridges. Tends to be lighter in weight

• Easy to remove (brittle) with de-icing equipment such as boots.

• More common to form in Stratified Clouds

RIME ON A CONVAIR

TYPES OF ICE• Clear ice has high advesive and cohesive

properties (harder to get rid of). Unlike rime it can spread from the leading edges, and in sever cases may cover the whole surface of the aircraft.

• Can look very transparent and glass-like to a very tough opaque surface. Clear ice is formed when large super-cooled water droplets collide with the air frame and freeze slowly after impact.

• The free water then flows back over the airfoil surfaces as it freezes at temperaturs not far below freezing. Tends to be heavier in weight than rime ice

CLEAR

• More common to form in Cummuliform Clouds

TYPES OF ICE• Mixed Ice is a mixture of Rime and clear ice

• frequently the temperature and the range of droplet sizes are such that the ice formed is a mixture.

ICING SEVERITY

INTENSITY OF ICING

• Trace - Ice becomes perceptible. The rate of accretion is slightly greater than the rate of sublimation. It is not hazardous even though de-icing/anti-icing equipment is not utilize, unless encountered for an extended period of time (over 1 hour)

• Light - The rate of accretion may create a problem if flight is prolonged in this environment (over one hour). Occasional use of de-icing/anti-icing equipment removes/prevents accretion.

INTENSITY OF ICING

• Moderate - the rate of accretion is such that even short encounters become potentially hazardous and the use of de-icing/anti-icing equipment, or diversion, is necessary.

• Severe - the rate of accretion is such that de-icing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary.

• What is considered moderate icing for one aircraft may be only light for another.

IT’S BAAADDD!

• 1. Increases weight

• 2. Reduces lift - changes the shape of the airfoil

• 3. Decreases thrust - effects prop

• 4. Increases drag - sticks up into the wind

TO GET ICING

• 1. Must have visible water• 2. Aircraft must be below freezing

• Icing is most frequent between +2C and -20C

• 3000 ft up or down will normally get you out of the ice.

LOOKS LIKE ICE TO ME, ZEKE

Better chance of icing

INDUCTION SYSTEM ICING

• Induction areas have small radius edges allowing ice to build up more rapidly

• Jet engine nacelles have heat

• Reciprocating engines have alternate air doors and carb heat

CARBURATOR ICE

• Adiabatic expansion in the venturi lowers air temp

• Moisture freezes restricting air flow

• Usually accumulates in curves or where there are obstructions in the flow

ICING AND CLOUD TYPES

• Low and middle clouds is usually where the ice is located

• freezing rain is the most hazardous icing condition

• High clouds have very little chance of icing since these clouds are composed of ice crystals

WHERE IS THE ICE?

• Ice is usually found within 5000 feet above the freezing level

• Usually only about 2000 - 3000 feet thick between 0º C and -15º C

• More rain means more ice when below freezing

SUPERCOOLED WATER

• May be found at temps as low as - 40º F (C)

• Freezing of pure water is called spontaneous nucleation

• enough molecules must join together in a ridged pattern to form an ice crystal

• it must grow to a critical size then other molecules will attach and the whole drop freezes

TERRAIN

• Mountain areas are good place to find ice

• up currents lift water droplets above the freezing level

• your usually flying higher to avoid the terrain and Presto ice

GROUND ICING

• Taxiing through puddles when temp is at or below 32

• accumulate water and or mud

• problem for retracts

• warm hanger is the only remedy

• deicing the wing may be accomplished with a 50/50 mix of isopropyl alcohol and water

• watch out for aircraft washers in winter

FREEZING RAIN

• Rain and drizzle tend to form severe clear ice.

FREEZING RAIN

• With a warm front approaching ice pellets on the surface generally lead to freezing rain on the surface or aloft prior to frontal passage.

FREEZING DRIZZLE

• Drizzle evaporates to some extent as it falls to the ground so the icing will be the most severe just near the cloud base.

• Ice pellets encounter during flight normally indicate warm air above

SNOW AND ICE CRYSTALS• Dry snow and ice crystals will not adhere to an

aircraft and will not normally cause icing. If the portion of the aircraft skin that they strike is above freezing, they may melt and freeze as they flow back over below-freezing portions of the aircraft.

• Flying in ice crystals can create a lot of static making radio communication difficult. Especially in the anvial of a TS.

• High clouds normally have a much lower ice accumulation rate.

ICING IN CLEAR AIR

• Hoar Frost - This term is used to indicate a white, feathery, crystalline formation that can cover the entire surface of the aircraft. It is similar to the ice that occasionally forms on metal surfaces such as car roofs during clear cool winter nights.

• Hoar frost forms by sublimation or, by water vapour which changes directly into ice crystals without going through the water stage. Occurs when moist air comes in contact with an object at temperatures below freezing.

ICING IN CLEAR AIR

• Hoar froast is typically going to form on aircraft when their surfaces are at temperatures sufficiently below freezing and the surround air is warmer and moist.

• Can also form in flight, especially during descents into warmer, moist air. Usually near fuel tanks.

FROST• Collects when the surface and the Dew

point are below freezing and the temp cools to the dew point

• little crystals form fingers that interrupt the boundary layer

• polish the frost smooth then your good to go

• Frost can cause early airflow separation resulting in a loss of lift.

AERODYNAMIC FACTORS

• Three things affect how much ice a wing will obtain.

• Curvature radii of wing, aircraft speed, and droplet size.

AERODYNAMIC FACTORS

• The large curvature radii (thick wings) creates less ice. The slower you are flying creates less ice. The smaller the droplet size = less ice.

AERODYNAMIC FACTORS

• Aerodynamic heating in faster aircraft can actually be to the point of making it impossible for ice to form on leading edges.

ENGINE ICING

• Carburetor Icing - frequently causes engine failure without warning. Can occur under conditions where structural icing may not occur and even in cloud less skys with temperatures as high as 25-30 degrees C.

• Carburetor Ice forms during vaporization of fuel, combined with the expansion of air as it passes through the carburetor. Of the two cooling processes, fuel vaporization causes the greater temperature drop. This may amount to as much as 40 degrees C

CARBURETOR ICING

DEICING AND ANTIICING• Deicing-used to remove ice from a surface.

• Anti-icing- the prevention of ice from forming

BOOTS

DEICING AND ANTIICING

• Deicing-used to remove ice from a surface. Hot Props, Leading edge/trailing edge boots, ice doors

• Anti-icing- the prevention of ice from forming. Alcohol chemicals, pitot-heat, stall warning vain heat, static port heat, wepping wings/windshield/props etc.

ACCUMULATES ON SMALL THIN AREAS FIRST

TAIL STALLS

ICING TIPS

BRAKING ACTION

QUESTIONS

• #1. Can water droplets exist as super-cooled water at temperatures below zero degrees C?

• yes

• #2. Name the three types of ice?

• Rime, Clear, Mixed

QUESTIONS

• #3 Which is easier to shed from an aircraft Rime or Clear Ice?

• Rime

• #4. If you have Ice pellets on the surface what can you have aloft?

• Freezing Rain

QUESTIONS

• #5. What are the four intensities of icing?

• Trace, Light, moderate, severe

• #6. Aerodynamic heating can keep the aircraft skin above freezing and prevent ice, but speeds in excess of 500 knots may be required (true/false)?

• True

QUESTIONS

• #7. Collection efficiency of wings is high for (sharp/shallow) leading edges, (high/low) speeds, and (large/small) droplets.