De-Icing/Anti-Icing and Step De-Icing/Anti-Icing
De-Icing/Anti-Icing
The most common techniques for removing frozen precipitation from aeroplane critical surfaces and protecting the aeroplane against re-contamination are accomplished with aeroplane de-icing and anti-icing fluids respectively. Any contamination found, shall be removed by a de-icing treatment. If anti-icing is also required, this treatment may be performed as a one-step or two-step de-icing/anti-icing of the relevant surfaces.
De-icing is a procedure by which frost, ice, snow or slush (i.e. the frozen contamination) is removed from an aeroplane to provide uncontaminated surfaces. Anti-icing is a procedure that provides protection against the formation of frost or ice and accumulation of snow on treated surfaces of the aeroplane for a limited period of time (hold over time - HOT).
The preferred spray pattern for applying the anti-ice fluid is outwards from the representative surface. Sprays are never directed at the APU, engine and other intakes/outlets. They are seldom directed at the cockpit windows; if any spray is directed to them and leaves a residue, it shall be removed. If applicable, switch OFF the windows heating prior to the cleaning of cockpit windows. De-icing/anti-icing fluids are only required until the aeroplane becomes airborne, after which the on-board de-icing/anti-icing system then operate.
To preserve hold over times, the de-icing/anti-icing process shall be continuous and as short as possible. Ensure that the de-icing/anti-icing procedures are performed at the latest possible time prior to take-off.
Depending on the aerodrome the aeroplane will be de-iced/anti-iced at the gate or at a central facility. De-icing/anti-icing at the gate is generally performed with engines OFF, while at the facility, in most cases, the engines are running. The relevant parts of OM Part C should be consulted for the procedure. Utmost care and vigilance shall be practised while adopting these procedures.
One-Step De-Icing/Anti-Icing
Generally, the one step process of de-icing is used when there isn’t any active precipitation occurring during de-icing. One step de-icing is completed with either Type I (orange in colour) or Type II fluids (clear or pale yellow).
These fluids provide limited anti-ice capability and have the very short hold over times in precipitation. Type I fluid cannot be relied upon during precipitation and should, therefore, be used as a de-icing fluid only.
Two-Step De-Icing/Anti-Icing
During conditions of ground icing, with falling precipitation adhering to the critical surfaces, anti-icing will be required.
Two-step de-icing/anti-icing (when the first step is performed with de-icing fluid): The correct fluid(s) shall be chosen with regard to ambient temperature.
After de-icing, a separate over-spray of anti-icing fluid shall be applied to protect the relevant surfaces thus providing maximum possible anti-ice capability.
The second step is performed with anti-icing fluid. The correct fluid concentration shall be chosen with regard to the desired hold over time and is dictated by outside air temperature and weather conditions (refer to QRH tables). The second step shall be performed before first step fluid freezes (typically within 3 min), if necessary area by area.
De-Icing/Anti-Icing Fluids
Important: If the colour of the fluid being applied to the aeroplane is NOT the colour anticipated, the procedure should be stopped and the situation investigated.
Type I
De-icing performance of the fluid is good. However, due to low viscosity, it provides only limited anti-icing protection during freezing precipitation. Due to its properties, Type I fluid forms a thin, liquid-wetting film on surfaces to which it is applied which, under certain weather conditions, gives a very limited hold over time. It is used predominantly for removing frozen deposits from aircraft surfaces, either as the first step in a two step operation or when precipitation has stopped. With this type of fluid, no additional protection is provided by increasing the concentration of fluid in the fluid/water mix (no extension in hold over time). This fluid has a high glycol content and low viscosity in its concentrated form.
Coloration: Light orange.
Type II
This fluid generally has lower glycol content in its concentrated form than Type I fluid due to the inclusion of a pseudo plastic thickening agent. This effectively means that when applied to the surface of an aircraft the viscosity is high, thus allowing the fluid to remain on and protect against freezing rain for a period of time. However, the increasing effect of the airflow over the wing surface during the take-off roll will effectively shear the fluid, reducing its viscosity and allowing it to readily flow off the critical surfaces. With this type of fluid, the hold over time can be extended by increasing the concentration of fluid in the fluid/water mix.
Coloration: Colourless or pale straw colour.
Type III
This fluid is similar in properties to Type II fluid.
Coloration: Light yellow.
Type IV
This type of fluid is similar in both composition and operation to Type II fluids. However, through the use of advanced thickening systems, it is able to provide more holdover time than Type II fluids, when used in concentrated forms. As with Type II fluids, the hold over time can be extended by increasing the concentration of fluid in the fluid/water mix.
Coloration: Emerald green.
Hold Over Time (HOT) Guidelines
The current Hold Over Time (HOT) tables for different types of fluid are contained in the GHM and QRH.
Hold over times are provided as a guide. Hold over time ranges are an estimate of the time that de-icing/anti-icing fluid will prevent the formation of frost or ice and the accumulation of snow on the unprotected surfaces of an aeroplane. HOT begins when the final application of de-icing/anti-icing fluid commences and when the de-icing/anti-icing fluid applied to the aeroplane loses its effectiveness (e.g., when ice begins to form on or in the fluid). The shortest time represents protection that may be available for medium levels precipitation and the longest for light precipitation.
It remains the Commander's responsibility to ensure that critical surfaces remain free of contamination before commencing the take-off roll.
HOT are influenced by a number of factors and the flight crew may need to use their judgment in their interpretation when considering the weather and other conditions. The effectiveness of de-icing/ anti-icing fluids is based on a number of variables (e.g. temperature, moisture content of the precipitation, wind, and the aeroplane skin temperature). The effects of these variables need to be taken into account by the Commander when establishing the HOT value.
The HOT tables are to be used for departure planning.
The time that the fluid remains effective in ensuring a safe take-off is the time from first application of anti-icing fluid on a clean wing until such time as ice crystals form or remain in the fluid creating a surface roughness for take-off that deteriorates the performance or controllability of the aeroplane.
HOT guidelines can be shortened to a more-conservative value if the Commander deems conditions warrant. Note that conditions can exist in which the HOT values are outside of the listed guidelines (see ‘CAUTION: No Hold Over Time guidelines exist.’ shown on the HOT’s). Present conditions may even deteriorate to the “no guideline” values so be aware of the conditions and modify the HOT values as required. In these rare situations, take-off is prohibited until conditions improve to within the guideline times shown on the applicable HOT.
Note that at any time an aeroplane exceeds the HOT, or in the view of the Commander that aeroplane de-icing/anti-icing is necessary, any residue from the previous treatment should be removed completely and a new de-icing/anti-icing treatment be applied.
Communications
In the interest of safety and passenger comfort, during the de-icing/anti-icing procedure, the flight crew shall maintain contact with the ground crew performing the de-icing operation. It is important that the de-icing operator is able to relay instructions to the Commander quickly and clearly.
Before Treatment
When the aeroplane is to be treated with the flight crew onboard, the flight and ground crews should confirm the following:
After configuring the aeroplane in preparation for de-icing/anti-icing the Commander shall advise the ground crew: »BRAKES SET, READY FOR DE-ICING/ANTI-ICING«.
After Treatment
The Commander shall be notified of the type of the de-/anti-icing treatment performed.
Following a de-icing/anti-icing treatment of the aeroplane and confirmation that the critical surface inspection has been completed, and that the aeroplane is free of frozen contaminants, the Commander will need the following information from the de-icing crew:
Aircraft Technical Log Entries
On receipt of the post de-icing check report, the Commander will complete the Aircraft Technical Log by entering all the relevant data including the type of fluid used and estimated HOT.
Note: The start time applicable, for the purposes of HOT, in the case of a Two-Step procedure is the start time of the second step.
The most common techniques for removing frozen precipitation from aeroplane critical surfaces and protecting the aeroplane against re-contamination are accomplished with aeroplane de-icing and anti-icing fluids respectively. Any contamination found, shall be removed by a de-icing treatment. If anti-icing is also required, this treatment may be performed as a one-step or two-step de-icing/anti-icing of the relevant surfaces.
De-icing is a procedure by which frost, ice, snow or slush (i.e. the frozen contamination) is removed from an aeroplane to provide uncontaminated surfaces. Anti-icing is a procedure that provides protection against the formation of frost or ice and accumulation of snow on treated surfaces of the aeroplane for a limited period of time (hold over time - HOT).
The preferred spray pattern for applying the anti-ice fluid is outwards from the representative surface. Sprays are never directed at the APU, engine and other intakes/outlets. They are seldom directed at the cockpit windows; if any spray is directed to them and leaves a residue, it shall be removed. If applicable, switch OFF the windows heating prior to the cleaning of cockpit windows. De-icing/anti-icing fluids are only required until the aeroplane becomes airborne, after which the on-board de-icing/anti-icing system then operate.
To preserve hold over times, the de-icing/anti-icing process shall be continuous and as short as possible. Ensure that the de-icing/anti-icing procedures are performed at the latest possible time prior to take-off.
Depending on the aerodrome the aeroplane will be de-iced/anti-iced at the gate or at a central facility. De-icing/anti-icing at the gate is generally performed with engines OFF, while at the facility, in most cases, the engines are running. The relevant parts of OM Part C should be consulted for the procedure. Utmost care and vigilance shall be practised while adopting these procedures.
One-Step De-Icing/Anti-Icing
Generally, the one step process of de-icing is used when there isn’t any active precipitation occurring during de-icing. One step de-icing is completed with either Type I (orange in colour) or Type II fluids (clear or pale yellow).
These fluids provide limited anti-ice capability and have the very short hold over times in precipitation. Type I fluid cannot be relied upon during precipitation and should, therefore, be used as a de-icing fluid only.
Two-Step De-Icing/Anti-Icing
During conditions of ground icing, with falling precipitation adhering to the critical surfaces, anti-icing will be required.
Two-step de-icing/anti-icing (when the first step is performed with de-icing fluid): The correct fluid(s) shall be chosen with regard to ambient temperature.
After de-icing, a separate over-spray of anti-icing fluid shall be applied to protect the relevant surfaces thus providing maximum possible anti-ice capability.
The second step is performed with anti-icing fluid. The correct fluid concentration shall be chosen with regard to the desired hold over time and is dictated by outside air temperature and weather conditions (refer to QRH tables). The second step shall be performed before first step fluid freezes (typically within 3 min), if necessary area by area.
De-Icing/Anti-Icing Fluids
Important: If the colour of the fluid being applied to the aeroplane is NOT the colour anticipated, the procedure should be stopped and the situation investigated.
Type I
De-icing performance of the fluid is good. However, due to low viscosity, it provides only limited anti-icing protection during freezing precipitation. Due to its properties, Type I fluid forms a thin, liquid-wetting film on surfaces to which it is applied which, under certain weather conditions, gives a very limited hold over time. It is used predominantly for removing frozen deposits from aircraft surfaces, either as the first step in a two step operation or when precipitation has stopped. With this type of fluid, no additional protection is provided by increasing the concentration of fluid in the fluid/water mix (no extension in hold over time). This fluid has a high glycol content and low viscosity in its concentrated form.
Coloration: Light orange.
Type II
This fluid generally has lower glycol content in its concentrated form than Type I fluid due to the inclusion of a pseudo plastic thickening agent. This effectively means that when applied to the surface of an aircraft the viscosity is high, thus allowing the fluid to remain on and protect against freezing rain for a period of time. However, the increasing effect of the airflow over the wing surface during the take-off roll will effectively shear the fluid, reducing its viscosity and allowing it to readily flow off the critical surfaces. With this type of fluid, the hold over time can be extended by increasing the concentration of fluid in the fluid/water mix.
Coloration: Colourless or pale straw colour.
Type III
This fluid is similar in properties to Type II fluid.
Coloration: Light yellow.
Type IV
This type of fluid is similar in both composition and operation to Type II fluids. However, through the use of advanced thickening systems, it is able to provide more holdover time than Type II fluids, when used in concentrated forms. As with Type II fluids, the hold over time can be extended by increasing the concentration of fluid in the fluid/water mix.
Coloration: Emerald green.
Hold Over Time (HOT) Guidelines
The current Hold Over Time (HOT) tables for different types of fluid are contained in the GHM and QRH.
Hold over times are provided as a guide. Hold over time ranges are an estimate of the time that de-icing/anti-icing fluid will prevent the formation of frost or ice and the accumulation of snow on the unprotected surfaces of an aeroplane. HOT begins when the final application of de-icing/anti-icing fluid commences and when the de-icing/anti-icing fluid applied to the aeroplane loses its effectiveness (e.g., when ice begins to form on or in the fluid). The shortest time represents protection that may be available for medium levels precipitation and the longest for light precipitation.
It remains the Commander's responsibility to ensure that critical surfaces remain free of contamination before commencing the take-off roll.
HOT are influenced by a number of factors and the flight crew may need to use their judgment in their interpretation when considering the weather and other conditions. The effectiveness of de-icing/ anti-icing fluids is based on a number of variables (e.g. temperature, moisture content of the precipitation, wind, and the aeroplane skin temperature). The effects of these variables need to be taken into account by the Commander when establishing the HOT value.
The HOT tables are to be used for departure planning.
The time that the fluid remains effective in ensuring a safe take-off is the time from first application of anti-icing fluid on a clean wing until such time as ice crystals form or remain in the fluid creating a surface roughness for take-off that deteriorates the performance or controllability of the aeroplane.
HOT guidelines can be shortened to a more-conservative value if the Commander deems conditions warrant. Note that conditions can exist in which the HOT values are outside of the listed guidelines (see ‘CAUTION: No Hold Over Time guidelines exist.’ shown on the HOT’s). Present conditions may even deteriorate to the “no guideline” values so be aware of the conditions and modify the HOT values as required. In these rare situations, take-off is prohibited until conditions improve to within the guideline times shown on the applicable HOT.
Note that at any time an aeroplane exceeds the HOT, or in the view of the Commander that aeroplane de-icing/anti-icing is necessary, any residue from the previous treatment should be removed completely and a new de-icing/anti-icing treatment be applied.
Communications
In the interest of safety and passenger comfort, during the de-icing/anti-icing procedure, the flight crew shall maintain contact with the ground crew performing the de-icing operation. It is important that the de-icing operator is able to relay instructions to the Commander quickly and clearly.
Before Treatment
When the aeroplane is to be treated with the flight crew onboard, the flight and ground crews should confirm the following:
- The fluid to be used;
- The extent of treatment;
- Any aeroplane specific procedures to be followed;
- Any other information needed to apply in HOT tables.
After configuring the aeroplane in preparation for de-icing/anti-icing the Commander shall advise the ground crew: »BRAKES SET, READY FOR DE-ICING/ANTI-ICING«.
After Treatment
The Commander shall be notified of the type of the de-/anti-icing treatment performed.
Following a de-icing/anti-icing treatment of the aeroplane and confirmation that the critical surface inspection has been completed, and that the aeroplane is free of frozen contaminants, the Commander will need the following information from the de-icing crew:
- Confirmation that all staff and equipment are clear of the aeroplane.
- Authorization to start engines (if applicable).
- Notification to switch to hand signals (if applicable).
Aircraft Technical Log Entries
On receipt of the post de-icing check report, the Commander will complete the Aircraft Technical Log by entering all the relevant data including the type of fluid used and estimated HOT.
Note: The start time applicable, for the purposes of HOT, in the case of a Two-Step procedure is the start time of the second step.
De-Icing/Anti-Icing and Step De-Icing/Anti-Icing
Reviewed by Aviation Lesson
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11:19 AM
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Reviewed by Aviation Lesson
on
11:19 AM
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