Introduction to De-icing and Anti-icing for Canadian Pilots

Every Canadian pilot is aware of the hazards posed by ice, frost, and snow adhering to an aircraft. Whether you're brushing off snow after a storm or dealing with frost early in the morning, contamination removal is a task every student pilot becomes familiar with. Depending on your aircraft type, you may have used brushes, ropes, mops, or basic de-icing fluids.

Photo by Buddy Photo on Unsplash

As you transition from training to commercial flying, managing winter operations becomes more complex. You’re not only removing contamination, but also dealing with active precipitation—such as snow, sleet, freezing rain, freezing drizzle, and freezing fog.

A Quick Refresher: Key Concepts

Before we dig deeper into de-icing and anti-icing procedures, it’s worth revisiting some critical safety basics:

  • Never attempt takeoff with any ice, frost, or snow on critical surfaces.
  • Critical surfaces include: wings, control surfaces, rotors, propellers, vertical and horizontal stabilizers, and, for aircraft with rear-mounted engines, the upper fuselage. Aircraft manufacturers may also designate other surfaces that must be free from contamination.
  • A pre-takeoff inspection is required if there’s any doubt about contamination on critical surfaces.
  • Even small amounts of contamination can reduce lift by up to 30% and increase drag by up to 40%.

De-Icing vs Anti-Icing

In Canadian operations, two primary fluid types are commonly used: Type I and Type IV.

  • Type I fluid is heated and applied with pressure to remove frost, ice, or snow. While it offers some short-term anti-icing properties, these are limited.
  • Type IV fluid is more viscous and is applied after de-icing to protect the aircraft from further contamination during taxi and prior to takeoff. It is designed to shear off during the takeoff roll.

Depending on the aircraft type, outside temperature, and fluid characteristics, some aircraft may experience performance degradation after application. Operators must account for this during pre-takeoff planning.

The duration that anti-icing fluid remains effective is referred to as the Holdover Time (HOT). This time depends on factors like the type of fluid, precipitation type, and precipitation intensity.

Understanding Holdover Time

Each year, Transport Canada publishes Holdover Time Guidelines, which pilots use to estimate how long anti-icing fluid remains effective from the start of the final application. Keep in mind:

  • These are guidelines, not guarantees.
  • Fluid effectiveness may vary with changing weather conditions.
  • The pilot-in-command is always responsible for ensuring the aircraft is free of contamination before takeoff.

Establishing HOT

During active precipitation, contamination is first removed with Type I fluid. When Type IV fluid is applied, the holdover time begins from the start of this final application.

To determine the HOT:

  1. Assess precipitation intensity. If the precipitation is snow, use the Visibility in Snow vs. Snowfall Intensity Chart found in the HOT guidelines.
  2. Do not use RVR to estimate intensity—use visibility in statute miles.
  3. Use the appropriate HOT table based on the fluid type and weather conditions.

Example METAR Analysis

METAR: CYHZ 290200Z 32005KT 1SM -SN SCT035 BKN079 M11/M12 A2984

From this, we know:

  • It’s dark outside.
  • Temperature is -11°C.
  • Visibility is 1 statute mile.

Using the visibility chart, this would be categorized as moderate snow, even though the METAR states “light snow.” This more conservative assessment is used when applying HOT tables.


HOT Table Example

Refer to the Type IV fluid table in the Transport Canada HOT guidelines. The exact fluid composition should be confirmed with your de-icing provider. Based on moderate snowfall, the guideline might indicate a holdover time of 30 to 55 minutes. It's worth noting that the chart below is for a generic Type IV fluid; however, different values may be found by referring to the specific HOT table for the manufacturer.


Important Notes:

  • Always read the footnotes—fluid-specific exceptions apply.
  • No holdover times are given for conditions such as heavy snow or moderate/freezing rain.
  • If conditions deteriorate, use the worst-case scenario.
  • HOT is not a countdown timer—it’s a guide. The pilot must confirm the aircraft is clean before takeoff.

Final Thoughts

Holdover time is affected by numerous factors—aircraft type, weather, and operator procedures all play a role. That’s why Transport Canada emphasizes the word “guide” in its documentation. At the end of the day, the responsibility lies with the pilot-in-command to ensure a clean aircraft at the time of takeoff.

References and Resources




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