Icing Conditions

Avoid it or escape it; Either way pilots are taught to prepare for ice at all costs.

Frost, snow, and freezing rain or drizzle can quickly impair the smooth surface of the aircraft airframe, disrupting air flow. By accumulating on the leading surfaces of the airplane, such as the tail, wings, propeller, windshield, antenna, vents, intakes and cowlings, it increases drag and decreases lift.

In moderate to severe conditions, carburettor ice can halt an engine, or an aircraft can accumulate such structural ice that it can no longer maintain controlled flight and stall, roll or pitch in a way that makes recovery impossible.

Meteorological and weather briefings, which contain icing forecasts, provide a fundamental indication of whether skies are clear and safe but pilots can still encounter unpredictable icing conditions that can put them and their passengers in danger.

Injuries sustained in US ice related accidents 2007-2017 46 7 11 36 Fatality None Minor Serious
38 35 25 2 Types of ice protection system installed on aircraft involved in US ice related accidents 2008-2017 None Boots Electrothermal Other (Non TKS)

Unlike other ice protection systems, TKS clears the entire surface of the airframe, eliminating any potential areas of ice, horns or spurs that can adversely effect flight aerodynamics.

Source: Aopa.org Accident database (all figures refer to US general aviation)

Ice Formation

Nearly all icing occurs in supercooled clouds that contain liquid drops below 0°C (32°F), which freeze on contact and adhere to the cold solid surface of the airframe.

Liquid water (supercooled drops) can exist in the atmosphere to -40°C, and freezing rain or drizzle pose the greatest threat; icing up an airframe and distorting aerodynamics in a matter of minutes.

Freezing Drizzle vs Freezing Rain

Freezing drizzle

Is formed in a cloud layer of droplets, in temperatures greater than -10°C. As these settle and fall within the cloud, they collide with each other to form droplets sizes greater than 0.05mm and smaller than 0.5mm. Like freezing rain they remain liquid until the contact a cold surface.

0.5mm 0.05mm

Freezing rain

Forms when water falls from a warm air mass through a subfreezing layer of air. It becomes supercooled and is defined as drops of 0.5mm or larger, with a usual diameter of 2mm, yet maintains a liquid state until it contacts a cold surface.

0.5mm 2mm

Types of Ice

Clear / Glaze Ice

Temperature 2°C to -10°C

  • Velocity: High
  • Appearance: Glossy, smooth and transparent, clear ice is dense and hard.
  • Formation: Large supercooled water droplets contact the aircraft, freezing gradually as they flow back over the surface. Larger accumulations may form ‘horns’ on the wing leading edge.

Rime

Temperature -15°C to -40°C

  • Velocity: Low
  • Appearance: Rough, milky and opaque, rime ice is porous and brittle.
  • Formation: Instantaneous or rapid freezing of small supercooled drops in their spherical shape as they strike the aircraft. Larger accumulations may form a streamlined extension of the wing.

Mixed

Temperature -10°C to -15°C

  • Velocity: Intermediate
  • Appearance: Rough and smooth areas with air pockets.
  • Formation: A mixture of large and small supercooled droplets forms a blend of rime and clear ice, often with ice particles becoming embedded in clear ice to form a very rough accumulation.

All structural icing types can cause a loss of stability and lift to the aircraft, as well as reducing thrust increasing drag, increasing weight and raising the speed of travel required to prevent wing stall.

Planning For Ice

Remaining aware of potential icing conditions is one of the best ways to avoid ice. Advanced weather reports, PIREPS, SIGMETS and AIRMETs are all invaluable tools for planning an ice-free flight.

But reports aren’t 100% fool proof, so how can you protect yourself against an inadvertent icing encounter? Or as a keen pilot, log those additional flight hours in times when visibility isn’t crystal clear?

Pneumatic de-icing systems, such as boots, are an energy efficient way to remove ice build-up but only address the aircraft’s leading edges. They cannot therefore, tackle any potential runback and only free the leading edges of ice directly after the de-icing cycle.

For an aircraft that is reliably equipped for all icing scenarios, the TKS® anti-icing system continuously prevents the formation of ice for all protected surfaces, including: wings, tails, propeller, windshield and struts. Providing fluid-based protection, TKS® exploits aerodynamic forces to drive an anti-ice fluid across the protected surfaces, before carrying the mixture away from the aircraft.