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Content

8.2.4. DE-ICING AND ANTI-ICING ON THE GROUND.............................................2

8.2.4.1. GLOSSARY / DEFINITIONS.....................................................................2

8.2.4.2. DE-/ANTI-ICING AWARENESS - THE BASIC REQUIREMENTS ...........5

8.2.4.3. DE-/ANTI-ICING AIRCRAFT ON THE GROUND: "WHEN, WHY AND

HOW"........................................................................................................6
8.2.4.3.1. Communication ..................................................................................6
8.2.4.3.2. Conditions which cause aircraft icing..................................................6
8.2.4.3.3. Checks to determine the need to de-ice/anti-ice ................................7
8.2.4.3.3.1. The clean wing concept...............................................................7
8.2.4.3.3.2. External inspection ......................................................................7
8.2.4.3.3.3. Clear ice phenomenon ................................................................8
8.2.4.3.3.4. General checks ...........................................................................8
8.2.4.3.4. Responsibility: the de-icing/anti-icing decision ...................................9
8.2.4.3.4.1. Maintenance / ground crew decision .........................................10
8.2.4.3.4.2. Pilots decision ...........................................................................10
8.2.4.3.5. The procedures to de-ice and anti-ice an aircraft .............................10
8.2.4.3.5.1. De-icing .....................................................................................10
8.2.4.3.5.2. Anti-icing ...................................................................................11
8.2.4.3.5.3. Limits and precautions ..............................................................12
8.2.4.3.5.4. Checks ......................................................................................15
8.2.4.3.5.5. Flight crew information - communication ...................................15
8.2.4.3.6. Pilot techniques ................................................................................23
8.2.4.3.6.1. Receiving aircraft ......................................................................23
8.2.4.3.6.2. Cockpit preparation ...................................................................23
8.2.4.3.6.3. Taxiing.......................................................................................24
8.2.4.3.6.4. Take-off .....................................................................................24
8.2.4.3.6.5. General remarks .......................................................................24

8.2.4.4. BACKGROUND INFORMATION ............................................................25

8.2.4.4.1. Aerodynamics and the contaminated wing .......................................25
8.2.4.4.2. Fluid characteristics and handling ....................................................28
8.2.4.4.2.1. De-icing/anti-icing fluids - characteristics ..................................28
8.2.4.4.2.2. Fluid handling............................................................................29
8.2.4.4.2.3. Environment and health ............................................................31
8.2.4.4.2.4. De-anti/anti-icing equipment......................................................32

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8.2.4. DE-ICING AND ANTI-ICING ON THE GROUND (JAR-OPS 1.345)

8.2.4.1. GLOSSARY / DEFINITIONS

The terms more specific to this section are defined here.

Anti-icing is a precautionary procedure, which provides protection against the formation of frost or ice and the
accumulation of snow on treated surfaces of the aircraft, for a limited period of time (holdover time).

Anti icing code describes the quality of the treatment the aircraft has received and provides information for
determining the holdover time.

Check is an examination of an item against a relevant standard by a trained and qualified person.

Clear ice is a coating of ice, generally clear and smooth, but with some air pockets. It is formed on exposed
objects at temperatures below, or slightly above, freezing temperature, with the freezing of super-cooled drizzle,
droplets or raindrops. See also "cold soak".

Cold soak: Even in ambient temperature between -2°C and at least +15°C, ice or frost can form in the presence
of visible moisture or high humidity if the aircraft structure remains at 0°C or below. Anytime precipitation falls on a
cold-soaked aircraft, while on the ground, clear icing may occur. This is most likely to occur on aircraft with integral
fuel tanks, after a long flight at high altitude. Clear ice is very difficult to visually detect and may break loose during
or after takeoff. The following can have an effect on cold soaked wings: Temperature of fuel in fuel cells, type and
location of fuel cells, length of time at high altitude flights, quantity of fuel in fuel cells, temperature of refuelled fuel
and time since refuelling.

Contaminated runway: A runway is considered to be contaminated when more than 25% of the runway surface
area (whether in isolated areas or not) within the required length and width being used is covered by the following:
- Surface water more than 3 mm (0.125 in) deep, or slush, or loose snow, equivalent to more than 3 mm
(0.125 in) of water; or
- Snow which has been compressed into a solid mass which resists further compression and will hold
together or break into lumps if picked up (compacted snow); or
- Ice, including wet ice

Damp runway: A runway is considered damp when the surface is not dry, but when the moisture on it does not
give it a shiny appearance.

De-icing is a procedure by which frost, ice, slush or snow is removed from the aircraft in order to provide clean
surfaces. This may be accomplished by mechanical methods, pneumatic methods, or the use of heated fluids.

De/Anti-icing is a combination of the two procedures, de-icing and anti-icing, performed in one or two steps.
A de-/anti-icing fluid, applied prior to the onset of freezing conditions, protects against the build up of frozen
deposits for a certain period of time, depending on the fluid used and the intensity of precipitation. With continuing
precipitation, holdover time will eventually run out and deposits will start to build up on exposed surfaces.
However, the fluid film present will minimise the likelihood of these frozen deposits bonding to the structure,
making subsequent de-icing much easier.

Dew point is the temperature at which water vapour starts to condense.

Dry runway: A dry runway is one which is neither wet nor contaminated, and includes those paved runways which
have been specially prepared with grooves or porous pavement and maintained to retain “effectively dry” braking
action, even when moisture is present.

Fluids (de-icing and anti-icing)

• De-icing fluids are:
a) Heated water
b) Newtonian fluid (ISO or SAE or AEA Type I in accordance with ISO 11075 specification)
c) Mixtures of water and Type I fluid
d) Non-Newtonian fluid (ISO or SAE or AEA Type II or IV in accordance with ISO 11078 specification)

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e) Mixtures of water and Type II or IV fluid

De-icing fluid is normally applied heated to ensure maximum efficiency
• Anti-icing fluids are:
a) Newtonian fluid (ISO or SAE or AEA Type I in accordance with ISO 11075 specification)
b) Mixtures of water and Type I fluid
c) Non-Newtonian fluid (ISO or SAE or AEA Type II or IV in accordance with ISO 11078 specification)
d) Mixtures of water and Type II or IV fluid
Anti-icing fluid is normally applied unheated on clean aircraft surfaces.

Freezing conditions are conditions in which the outside air temperature is below +3°C (37.4F) and visible
moisture in any form (such as fog with visibility below 1.5 km, rain, snow, sleet or ice crystals) or standing water,
slush, ice or snow is present on the runway.

Freezing fog (Metar code: FZFG) is a suspension of numerous tiny supercooled water droplets which freeze upon
impact with ground or other exposed objects, generally reducing the horizontal visibility at the earth’s surface to
less than 1 km (5/8 mile).

Freezing drizzle (Metar code: FZDZ) is a fairly uniform precipitation composed exclusively of fine drops - diameter
less than 0.5 mm (0.02 inch) - very close together which freeze upon impact with the ground or other objects.

Freezing rain (Metar code: FZRA) is a precipitation of liquid water particles which freezes upon impact with the
ground or other exposed objects, either in the form of drops of more than 0.5 mm (0.02 inch) diameter or smaller
drops which, in contrast to drizzle, are widely separated.

Friction coefficient: Relationship between the friction force acting on the wheel and the normal force on the
wheel. The normal force depends on the weight of the aircraft and the lift of the wings.

Frost is a deposit of ice crystals that form from ice-saturated air at temperatures below 0°C (32°F) by direct
sublimation on the ground or other exposed objects. Hoar frost (a rough white deposit of crystalline appearance
formed at temperatures below freezing point) usually occurs on exposed surfaces on a cold and cloudless night. It
frequently melts after sunrise; if it does not, an approved de-icing fluid should be applied in sufficient quantities to
remove the deposit. Generally, hoar frost cannot be cleared by brushing alone. Thin hoar frost is a uniform white
deposit of fine crystalline texture, which is thin enough to distinguish surface features underneath, such as paint
lines, markings, or lettering.

Glaze ice or rain ice is a smooth coating of clear ice formed when the temperature is below freezing and freezing
rain contacts a solid surface. It can only be removed by de-icing fluid; hard or sharp tools should not be used to
scrape or chip the ice off as this can result in damage to the aircraft.

Grooved runway: see dry runway.

Hail (Metar code: GR) is a precipitation of small balls or pieces of ice, with a diameter ranging from 5 to 50 mm
(0.2 to 2.0 inches), falling either separately or agglomerated.

Holdover time is the estimated time anti-icing fluid will prevent the formation of frost or ice and the accumulation
of snow on the protected surfaces of an aircraft, under (average) weather conditions mentioned in the guidelines
for holdover time.
The ISO/SAE specification states that the start of the holdover time is from the beginning of the anti-icing
treatment.

Ice Pellets (Metar code PE) is a precipitation of transparent (sleet or grains of ice) or translucent (small hail)
pellets of ice, which are spherical or irregular, and which have a diameter of 5 mm (0.2 inch) or less. The pellets of
ice usually bounce when hitting hard ground.

Icing conditions may be expected when the OAT (on the ground and for takeoff) or when TAT (in flight) is at or
below 10°C, and there is visible moisture in the air (such as clouds, fog with low visibility of one mile or less, rain,
snow, sleet, ice crystals) or standing water, slush, ice or snow is present on the taxiways or runways. (AFM
definition)

Icy runway: A runway is considered icy when its friction coefficient is 0.05 or below.

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Light freezing rain is a precipitation of liquid water particles which freezes upon impact with exposed objects, in
the form of drops of more than 0.5 mm (0.02 inch) which, in contrast to drizzle, are widely separated. Measured
intensity of liquid water particles are up to 2.5mm/hour (0.10 inch/hour) or 25 grams/dm2/hour with a maximum of
2.5 mm (0.10 inch) in 6 minutes.

Non-Newtonian fluids have characteristics that are dependent upon an applied force. In this instance it is the
viscosity of Type II and IV fluids which reduces with increasing shear force. The viscosity of Newtonian fluids
depends on temperature only.

One step de-/anti-icing is carried out with an anti-icing fluid, typically heated. The fluid used to de-ice the aircraft
remains on aircraft surfaces to provide limited anti-ice capability.

Precipitation: Liquid or frozen water that falls from clouds as rain, drizzle, snow, hail, or sleet.
• Continuous: Intensity changes gradually, if at all.
• Intermittent: Intensity changes gradually, if at all, but precipitation stops and starts at least
once within the hour preceding the observation.

Precipitation intensity is an indication of the amount of precipitation falling at the time of observation. It is
expressed as light, moderate or heavy. Each intensity is defined with respect to the type of precipitation occurring,
based either on rate of fall for rain and ice pellets or visibility for snow and drizzle. The rate of fall criteria is based
on time and does not accurately describe the intensity at the time of observation.

Rain (Metar code: RA) is a precipitation of liquid water particles either in the form of drops of more than 0.5 mm
(0.02 inch) diameter or of smaller widely scattered drops.

Rime (a rough white covering of ice deposited from fog at temperature below freezing). As the fog usually consists
of super-cooled water drops, which only solidify on contact with a solid object, rime may form only on the windward
side or edges and not on the surfaces. It can generally be removed by brushing, but when surfaces, as well as
edges, are covered it will be necessary to use an approved de-icing fluid.

Saturation is the maximum amount of water vapour allowable in the air. It is about 0.5 g/m3 at - 30°C and 5
g/m3 at 0°C for moderate altitudes.

Shear force is a force applied laterally on an anti-icing fluid. When applied to a Type II or IV fluid, the shear force
will reduce the viscosity of the fluid; when the shear force is no longer applied, the anti-icing fluid should recover its
viscosity. For instance, shear forces are applied whenever the fluid is pumped, forced through an orifice or when
subjected to airflow. If excessive shear force is applied, the thickener system could be permanently degraded and
the anti-icing fluid viscosity may not recover and may be at an unacceptable level.

SIGMET is an information issued by a meteorological watch office concerning the occurrence, or expected
occurrence, of specified en-route weather phenomena which may affect the safety of aircraft operations.

Sleet is a precipitation in the form of a mixture of rain and snow. For operation in light sleet treat as light freezing
rain.

Slush is water saturated with snow, which spatters when stepping firmly on it. It is encountered at temperature
around 5°C.

Snow (Metar code SN): Precipitation of ice crystals, most of which are branched, star-shaped, or mixed with
unbranched crystals. At temperatures higher than about -5°C (23°F), the crystals are generally agglomerated into
snowflakes.
• Dry snow: Snow which can be blown if loose or, if compacted by hand, will fall apart upon release; specific
gravity: up to but not including 0.35.
Dry snow is normally experienced when temperature is below freezing and can be brushed off easily from the
aircraft.
• Wet snow: Snow which, if compacted by hand, will stick together and tend to or form a snowball. Specific
gravity: 0.35 up to but not including 0.5.
Wet snow is normally experienced when temperature is above freezing and is more difficult to remove from
the aircraft structure than dry snow being sufficiently wet to adhere.

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• Compacted snow: Snow which has been compressed into a solid mass that resists further compression and
will hold together or break up into chunks if picked up. Specific gravity: 0.5 and over.

Snow grains (Metar code: SG) is a precipitation of very small white and opaque grains of ice. These grains are
fairly flat or elongated. Their diameter is less than 1 mm (0.04 inch). When the grains hit hard ground, they do not
bounce or shatter.

Snow pellets (Metar code: GS) is a precipitation of white and opaque grains of ice. These grains are spherical or
sometimes conical. Their diameter is about 2 to 5 mm (0.1 to 0.2 inch). Grains are brittle, easily crushed; they
bounce and break on hard ground.

Supercooled water droplets is a condition where water remains liquid at negative Celsius temperature.
Supercooled drops and droplets are unstable and freeze upon impact.

Two step de-icing/anti-icing consists of two distinct steps. The first step (de-icing) is followed by the second step
(anti-icing) as a separate fluid application. After de-icing a separate overspray of anti-icing fluid is applied to
protect the relevant surfaces, thus providing maximum possible anti-ice capability.

Visible moisture: Fog, rain, snow, sleet, high humidity (condensation on surfaces), ice crystals or when taxiways
and/or runways are contaminated by water, slush or snow.

Visual meteorological conditions: Meteorological conditions expressed in terms of visibility, distance from cloud,
and ceiling, equal to or better than specified minima.

Wet runway: A runway is considered wet when the runway surface is covered with water, or equivalent, less than
or equal to 3 mm or when there is sufficient moisture on the runway surface to cause it to appear reflective, but
without significant areas of standing water.

8.2.4.2. DE-/ANTI-ICING AWARENESS - THE BASIC REQUIREMENTS

• Responsibility

The person technically releasing the aircraft is responsible for the performance and
verification of the results of the treatment. The responsibility of accepting the performed
treatment lies, however, with the pilot in command. The transfer of responsibility takes
place at the moment the aircraft starts moving under its own power.

• Necessity

Icing conditions on ground can be expected when air temperatures approach or fall
below freezing and when moisture or ice occurs in the form of either precipitation or
condensation.
Aircraft-related circumstances could also result in ice accretion when humid air at
temperatures above freezing comes in contact with cold structure.

• Checks

Have you enough information and adequate knowledge in order to dispatch?

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8.2.4.3. DE-/ANTI-ICING AIRCRAFT ON THE GROUND: "WHEN, WHY AND

HOW"

8.2.4.3.1. Communication

To get the highest possible visibility concerning de-/anti-icing, a good level of

communication between ground and flight crews is necessary.
Any observations or points significant to the flight or ground crew should be reported
between them.
These observations may concern the weather or aircraft-related circumstances or other
factors important for the dispatch of the aircraft.
Several incidents have shown that increased awareness of one part of the flight/ground
crew team could have avoided a critical situation.
The minimum requirements of communication must comprise the details of when the
aircraft was de-iced and the quality of treatment (type of fluid).
This is summarised by the anti-icing code.

Remember: Uncertainty should not be resolved by transferring responsibility. The

only satisfactory answer is clear communication.

8.2.4.3.2. Conditions which cause aircraft icing

• Weather-related conditions

Weather conditions dictate the "when" of the "when, why and how" of aircraft de-/anti-
icing on the ground.
Icing conditions on the ground can be expected when air temperatures fall below
freezing and when moisture or ice occurs in the form of either precipitation or
condensation. Precipitation may be rain, sleet or snow. Frost can occur due to the
condensation of fog or mist.

To these weather conditions must be added further phenomena that can also result in
aircraft ice accretion on the ground.

• Aircraft-related conditions

The concept of icing is commonly associated only with exposure to inclement weather.
However, even if the OAT is above freezing point, ice or frost can form if the aircraft
structure is below 0° C (32° F) and moisture or relatively high humidity is present.

With rain or drizzle falling on sub-zero structure, a clear ice layer can form on the wing
upper surfaces when the aircraft is on the ground. In most cases this is accompanied
by frost on the underwing surface.

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8.2.4.3.3. Checks to determine the need to de-ice/anti-ice

8.2.4.3.3.1. The clean wing concept

Why de-ice/anti-ice on ground? The aircraft performance is certified based upon an

uncontaminated or clean structure. Ice, snow or frost accumulations will disturb the
airflow, affecting lift and drag and also increasing weight. The result on performance
can be dramatic.

Aircraft preparation for service begins and ends with a thorough inspection of the
aircraft exterior. The aircraft and especially its surfaces providing lift, controllability and
stability must be aerodynamically clean. Otherwise, safe operation is not possible.

An aircraft ready for flight must not have ice, snow, slush or frost adhering to its
surfaces. Exceptions are sometimes allowed. Refer to FCOM:

- For A300 / A310 / A300-600:

Procedures and Techniques chapter - Inclement weather operations - Aircraft
preparation for cold weather operation.

- For A320 family / A330 / A340

Supplementary techniques chapter - Adverse weather - Cold weather

But the critical flying surfaces must definitely be free of any contamination.

8.2.4.3.3.2. External inspection

An inspection of the aircraft must visually cover all critical parts of the aircraft and be
performed from points offering a clear view of these parts.

These parts are especially:

- wing surfaces including leading edges
- horizontal stabiliser upper and lower surface
- vertical stabiliser and rudder
- fuselage
- air data probes
- static vents
- angle-of-attack sensors
- control surface cavities
- engines
- generally intakes and outlets
- landing gear and wheel bays.

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8.2.4.3.3.3. Clear ice phenomenon

Under certain conditions, a clear ice layer or frost can form on the wing upper surfaces
when the aircraft is on the ground. In most cases this is accompanied by frost on the
underwing surface. Severe conditions occur with precipitation when sub-zero fuel is in
contact with the wing upper surface skin panels. The clear ice accumulations are
very difficult to detect from ahead of the wing or behind during walk-around,
especially in poor lighting and when the wing is wet. The leading edge may not feel
particularly cold. The clear ice may not be detected from the cabin either because wing
surface details show through.

The following factors contribute to the formation intensity and the final thickness of the
clear ice layer:

- Low temperature of fuel that was added to the aircraft during the previous ground
stop and/or the long airborne time of the previous flight resulting in a situation that
the remaining fuel in the wing tanks is below 0° C.
- Abnormally large amount of remaining cold fuel in wing tanks causing the fuel level
to be in contact with the wing upper surface panels as well as the lower surface,
especially in the wing tank area.
- Temperature of fuel added to the aircraft during the current ground stop, adding
(relatively) warm fuel can melt dry, falling snow with the possibility of re-freezing.
Drizzle/rain and ambient temperatures around 0°C on the ground is very critical.
Heavy freezing has been reported during drizzle/rain even at temperatures of 8 to
14° C (46 to 57° F). The use of thermal leading edge anti-icing may melt falling dry
snow that re-freezes later.

The areas most vulnerable to freezing are:

- the wing root area between the front and rear spars,
- any part of the wing that will contain unused fuel after flight,
- the areas where different structures of the wing are concentrated (a lot of cold
metal), such as areas above the spars and the main landing gear doubler plate.

8.2.4.3.3.4. General checks

A recommended procedure to check the wing upper surface is to place high enough
steps as close as possible to the leading edge and near the fuselage, and climb the
steps so that you can touch a wide sector of the tank area by hand. If clear ice is
detected, the wing upper surface should be de-iced and then re-checked to ensure that
all ice deposits have been removed.

It must always be remembered that below a snow / slush / anti-icing fluid layer
there can be clear ice.

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During checks on ground, electrical or mechanical ice detectors should only be used as
a back-up advisory. They are not a primary system and are not intended to replace
physical checks.
Ice can build up on aircraft surfaces when descending through dense clouds or
precipitation during an approach.

When ground temperatures at the destination are low, it is possible that when flaps are
retracted accumulations of ice may remain undetected between stationary and
moveable surfaces. It is therefore important that these areas are checked prior to
departure and any frozen deposits removed.
Under freezing fog conditions it is necessary for the rear side of the fan blades to be
checked for ice build-up prior to start-up. Any deposits discovered should be removed
by directing air from a low flow hot air source, such as a cabin heater, onto the affected
areas.

When slush is present on runways, inspect the aircraft when it arrives at the ramp for
slush/ice accumulations. If the aircraft arrives at the gate with flaps in a position other
than fully retracted, those flaps which are extended must be inspected and, if
necessary, de-iced before retraction.

The flight crew operating manual for individual aircraft types may allow take-off with a
certain amount of frost on certain parts of the aircraft (refer to the individual FCOM).

It is important to note that the rate of ice formation is considerably increased by the
presence of an initial depth of ice. Therefore, if icing conditions are expected to occur
along the taxi and take-off path, it is necessary to ensure that all ice and frost is
removed before flight. This consideration must extend the awareness of flight crew to
include the condition of the taxiway, runway and adjacent areas since surface
contamination and blown snow are potential causes for ice accretion equal to natural
precipitation.

8.2.4.3.4. Responsibility: the de-icing/anti-icing decision

• Maintenance responsibility

The information report (de-icing/anti-icing code - see 8.2.4.3.5.5) given to the cockpit is
a part of the technical airworthiness of the aircraft. The person releasing the aircraft is
responsible for the performance and verification of the results of the de/anti-icing
treatment. The responsibility of accepting the performed treatment lies, however, with
the Commander.

• Operational responsibility

The general transfer of operational responsibility takes place at the moment the aircraft
starts moving by its own power.

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8.2.4.3.4.1. Maintenance / ground crew decision

The responsible ground crew member should be clearly nominated. He should check
the aircraft for the need to de-ice. He will, based on his own judgement, initiate de-/anti-
icing, if required, and he is responsible for the correct and complete de-icing and/or
anti-icing of the aircraft.

8.2.4.3.4.2. Pilots decision

As the final decision rests with the Commander, his request will supersede the ground
crew member's judgement not to de-ice.
As the Commander is responsible for the anti-icing condition of the aircraft during
ground manoeuvring prior to takeoff, he can request another anti-icing application with
a different mixture ratio to have the aircraft protected for a longer period against
accumulation of precipitation. Equally, he can simply request a repeat application.
Therefore the Commander should take into account forecasted or expected weather
conditions, taxi conditions, taxi times, holdover time and other relevant factors. The
Commander must, when in doubt about the aerodynamic cleanliness of the aircraft,
perform (or have performed) an inspection or simply request a further de-/anti-icing.

Even when responsibilities are clearly defined and understood, sufficient

communication between flight and ground crews is necessary. Any observation
considered valuable should be mentioned to the other party to have redundancy in the
process of decision making.

8.2.4.3.5. The procedures to de-ice and anti-ice an aircraft

When aircraft surfaces are contaminated by frozen moisture, they must be de-iced prior
to dispatch. When freezing precipitation exists and there is a risk of precipitation
adhering to the surface at the time of dispatch, aircraft surfaces must be anti-iced. If
both anti-icing and de-icing are required, the procedure may be performed in one or
two steps. The selection of a one or two step process depends upon weather
conditions, available equipment, available fluids and the holdover time required to be
achieved.
When a large holdover time is expected or needed, a two-step procedure using
undiluted fluid should always be considered for the second step.

8.2.4.3.5.1. De-icing

Ice, snow, slush or frost may be removed from aircraft surfaces by heated fluids or
mechanical methods or any other approved methods such as infrared de-icing which is
being developed.

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For maximum effect, fluids shall be applied close to the aircraft surfaces to minimise
heat loss. Different methods to efficiently remove frost, snow, and ice are described in
detail in the ISO method specification.

• General de-icing fluid application strategy

The following guidelines describe effective ways to remove snow and ice.
However, certain aircraft may require unique procedures to accommodate specific
design features. The relevant aircraft maintenance or servicing manuals should be
consulted.

Wings/horizontal stabilisers: Spray from the tip towards the root, from the highest
point of the surface camber to the lowest.

Vertical surfaces: Start at the top and work downward.

Fuselage: Spray along the top centreline and then outboard; avoid spraying directly
onto windows.

Landing gear and wheel bays: Keep application of de-icing fluid in this area to a
minimum. It may be possible to mechanically remove accumulations such as blown
snow. However, where deposits have bonded to surfaces they can be removed using
hot air or by careful spraying with hot de-icing fluids. It is not recommended to use a
high-pressure spray.

Engines: Deposits of snow should be mechanically removed (for example using a

broom or brush) from engine intakes prior to departure. Any frozen deposits that may
have bonded to either the lower surface of the intake or the fan blades may be
removed by hot air or other means recommended by the engine manufacturer.

8.2.4.3.5.2. Anti-icing

Applying anti-icing protection means that ice, snow or frost will, for a period of time,
be prevented from adhering to, or accumulating on, aircraft surfaces. This is done by
the application of anti-icing fluids.

Anti-icing fluid should be applied to the aircraft surfaces when freezing rain,
snow or other freezing precipitation is falling and adhering at the time of aircraft
dispatch.

For an effective anti-icing protection an even film of undiluted fluid is required over the
aircraft surfaces which are clean or which have been de-iced. For maximum anti-icing
protection undiluted, unheated Type II or IV fluid should be used. The high fluid
pressures and flow rates normally associated with de-icing are not required for this
operation and, where possible, pump speeds should be reduced accordingly. The
nozzle of the spray gun should be adjusted to give a medium spray.

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The anti-icing fluid application process should be continuous and as short as possible.
Anti-icing should be carried out as near to the departure time as is operationally
possible in order to maintain holdover time.
In order to control the uniformity, all horizontal aircraft surfaces must be visually
checked during application of the fluid. The amount required will be a visual indication
of fluid just beginning to drip off the leading and trailing edges.
Most effective results are obtained by commencing on the highest part of the wing
section and covering from there towards the leading and trailing edges. On vertical
surfaces, start at the top and work down.
Surfaces to be protected during anti-icing are:
- Wing upper surface
- Horizontal stabiliser upper surface
- Vertical stabiliser and rudder
- Fuselage depending upon amount and type of precipitation

Type I fluids have limited effectiveness when used for anti-icing purposes. Little
benefit is gained from the minimal holdover time generated.

8.2.4.3.5.3. Limits and precautions

• Aircraft related limits

The use of Type II or IV fluids in 100% concentration or 75/25 mixture is limited to
aircraft with a rotation speed (VR) higher than 85kt. This is to assure the sufficient flow-
off of the fluid during take-off.

• Temperature limits
When performing two-step de-icing / anti-icing, the freezing point of the heated fluid
used for the first step must not be more than 3°C above ambient temperature.
The freezing point of the Type I fluid mixture used for either one-step de-icing / anti-
icing or as the second step in a two-step operation shall be at least 10°C below the
ambient temperature.
Type II and IV fluids used as de-icing / anti-icing agents have a lower temperature
application limit of -25°C.
The application limit may be lower, provided that a 7°C buffer is maintained between
the freezing point of the undiluted fluid and the outside air temperature. Freezing points
are provided in the fluid manufacturers documentation.

• Application limits
Under no circumstances can an aircraft that has been anti-iced receive a further
coating of anti-icing fluid directly on top of the existing film. In continuing
precipitation, the original anti-icing coating will be diluted at the end of the holdover time
and re-freezing could begin. Also a double anti-ice coating should not be applied
because the flow-off characteristics during take-off may be compromised.
Should it be necessary for an aircraft to be re-protected prior to the next flight, the
external surfaces must first be de-iced with a hot fluid mix before a further application of
anti-icing fluid is made.

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• Precautions

The fluids used should be limited to those complying respectively with standards AMS
1424B/ISO 11075 and AMS 1428C/ISO 11078 for Type I, Type II and Type IV.
AMS 1428C reflects the additional requirements for fluid dry out and flow off behaviour
for type IV fluids.
The Airbus consumable materials list and Aircraft Maintenance Manual reflect the new
1428C standard.

With specific regard to the application of Type IV fluids, and indeed Type II fluids,
special care needs to be taken. Repeated application in dry conditions, as a preventive
measure, may leave a residue that when exposed to precipitation can re-hydrate. This
takes the form of a high freeze point gel in aerodynamically quiet areas of the aircraft.
This gel could lead to the restricted movement of control surfaces. To date this has only
been reported on aircraft types with unpowered flying controls and has not been
reported on Airbus aircraft.

Therefore the aircraft should be frequently cleaned of any residue and/or de-iced
using a heated Type I fluid or hot water prior to the application of Type II or Type IV
fluids (two step process).
De/anti-icing activities should only be carried out by personnel that are fully trained to
ISO, SAE or AEA standards and furthermore that those persons understand their
responsibilities and are authorised/approved to carry out such activities.

For de/anti-icing activities the following standards should be followed:

- ISO 11076 aircraft de-icing/anti-icing methods with fluids.

- SAE ARP 4737E aircraft de-icing/anti-icing methods with fluids.
- AEA recommendations for the de-icing/anti-icing of aircraft on ground,

In order to fully benefit from the longer hold over times of Type IV fluids, they must be
used undiluted. Diluted Type IV are only tested to the same specification as a Type II
fluid.
For holdover times and recommendations on Type IV fluid application (in addition to
those mentioned in Tables 2 and 5), operators should refer to one of the following
documents:

- AEA recommendations for de-icing/anti-icing of aircraft on ground.

This document can be obtained from: www.aea.be/special publications

- FSAT bulletin XX-07 (XX = year), entitled FAA-approved de-icing program updates,
winter 20XX. This document can be obtained from: www.faa.gov./avr/afs/fsat

- Canadian aviation regulation standard 622-11, entitled "ground icing operations"

This document can be obtained from: www.tc.gc.ca/aviation/regserv/carac

All three documents provide the updated SAE/AEA Type IV fluids holdover times
guidelines.

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The aircraft must always be treated symmetrically - the left hand and right hand
sides (e.g. left wing/right wing) must receive the same and complete treatment.

Engines are usually not running or are at idle during treatment. Air conditioning should
be selected OFF. The APU may be run for electrical supply but the bleed air valve
should be closed.

All reasonable precautions must be taken to minimise fluid entry into engines, other
intakes / outlets and control surface cavities.

Do not spray de-icing / anti-icing fluids directly onto exhausts or thrust reversers.
De-icing / anti-icing fluid should not be directed into the orifices of pitot heads, static
vents or directly onto angle-of-attack sensors.
Do not direct fluids onto flight deck or cabin windows because this can cause cracking
of acrylics or penetration of the window sealing.

All doors and windows must be closed to prevent:

- galley floor areas being contaminated with slippery de-icing/anti-icing fluids
- upholstery becoming soiled.

Any forward area from which fluid may blow back onto windscreens during taxi or
subsequent take-off should be free of fluid residues prior to departure. If Type II or IV
fluids are used, all traces of the fluid on flight deck windows should be removed prior to
departure, particular attention being paid to windows fitted with wipers.

De-icing/anti-icing fluid can be removed by rinsing with clear water and wiping with a
soft cloth. Do not use the windscreen wipers for this purpose. This will cause
smearing and loss of transparency.

Landing gear and wheel bays must be kept free from build-up of slush, ice or
accumulations of blown snow.
Do not spray de-icing fluid directly onto hot wheels or brakes.

When removing ice, snow or slush from aircraft surfaces, care must be taken to prevent
it entering and accumulating in auxiliary intakes or control surface hinge areas, i.e.
remove snow from wings and stabiliser surfaces forward towards the leading edge and
remove from ailerons and elevators back towards the trailing edge.

Do not close any door until all ice has been removed from the surrounding area.

A functional flight control check using an external observer may be required after
de-icing / anti-icing. This is particularly important in the case of an aircraft that has been
subjected to an extreme ice or snow covering.

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8.2.4.3.5.4. Checks

• Final check before aircraft dispatch

No aircraft should be dispatched for departure under icing conditions or after a de-icing
/ anti-icing operation unless the aircraft has received a final check by a responsible
authorised person.

The inspection must visually cover all critical parts of the aircraft and be performed from
points offering sufficient visibility on these parts (e.g. from the de-icer itself or another
elevated piece of equipment). It may be necessary to gain direct access to physically
check (e.g. by touch) to ensure that there is no clear ice on suspect areas.

• Pre takeoff check

When freezing precipitation exists, it may be appropriate to check aerodynamic

surfaces just prior to the aircraft taking the active runway or initiating the take-off
roll in order to confirm that they are free of all forms of frost, ice and snow. This is
particularly important when severe conditions are experienced, or when the published
holdover times have either been exceeded or are about to run out.
When deposits are in evidence it will be necessary for the de-icing operation to be
repeated.
If the take-off location cannot be reached within a reasonable time and/or a reliable
check of the wing upper surface status cannot be made from inside the aircraft,
consider a repeat aircraft treatment.

If aircraft surfaces cannot adequately be inspected from inside the aircraft, it is

desirable to provide a means of assisting the flight crew in determining the condition of
the aircraft. The inspection should be conducted as near as practical to the beginning
of the departure runway.

When airport configuration allows, it is desirable to provide de-icing/anti-icing and

inspection of aircraft near the beginning of departure runways to minimise the time
interval between aircraft de-icing / anti-icing and take-off, under conditions of freezing
precipitation.

8.2.4.3.5.5. Flight crew information - communication

No aircraft should be dispatched for departure after a de-icing / anti-icing operation

unless the flight crew has been notified of the type of de-icing / anti-icing
operation performed. The ground crew must make sure that the flight crew has been
informed. The flight crew should make sure that they have the information.

This information includes the results of the final inspection by qualified personnel,
indicating that the aircraft critical parts are free of ice, frost and snow. It also includes

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the necessary anti-icing codes to allow the flight crew to estimate the holdover time to
be expected under the prevailing weather conditions.

• Anti-icing codes

It is essential that flight crew receives clear information from ground personnel as to the
treatment applied to the aircraft.
The AEA (Association of European Airlines) recommendations and the SAE and ISO
specifications promote the standardised use of a four-element code. This gives flight
crew the minimum details to assess holdover times. The use of local time is preferred
but, in any case, statement of the reference is essential. This information must be
recorded and communicated to the flight crew by referring to the last step of the
procedure.

Examples of anti-icing codes:

AEA Type II/75/16.43 local/FRA 19 Jan 02

AEA Type II : Type of fluid used

75 : Percentage of fluid/water mixtures by volume 75% fluid/25% water
16.43 : Local time of start of last application
19 Jan 02 : Date

ISO Type I/50:50/06.30 UTC/ 19 Jan 02

50:50 : 50% fluid / 50 % water

06.30 : Time (UTC) of start of last application

• Standard communication terminology

- De-icing/anti-icing supervisor:
"Set parking brakes, confirm aircraft is ready for treatment, inform any special
requests"
- Commander:
"Brakes are set, you may begin treatment and observe… (any special requests
like: ice under wing/flaps, clear ice on top of wing, snow on fuselage, ice on
landing gear, anti-ice type IV…)"
- De-icing/anti-icing supervisor:
"We begin treatment and observe…(special requests mentioned above). I will
call you back when ready".
Only after equipment is cleared from aircraft and all checks are made:
- De-icing/anti-icing supervisor:
"De-icing/anti-icing completed. Anti-icing code is:… (plus any additional info
needed). I am disconnecting, standby for clear signal at right/left and/or contact
ground/tower for taxi clearance".
- Commander:
"De-icing/anti-icing completed, anti-icing code is…".

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• Fluid application and holdover time guidelines

Holdover protection is achieved by anti-icing fluids remaining on and protecting aircraft

surfaces for a period of time.
With a one step de/anti-icing operation holdover begins at the start of the operation and
with two-step, at the start of the second (anti-icing) step. Holdover time will have
effectively run out, when frozen deposits start to form/accumulate on aircraft surfaces.

Due to its properties Type I fluid forms a thin liquid wetting film, which gives a rather
limited holdover time, depending on weather conditions. With this type of fluid
increasing the concentration of fluid in the fluid/water mix would provide no additional
holdover time.

Type II and Type IV fluids contain a thickener which enables the fluid to form a thicker
liquid wetting film on external surfaces. This film provides a longer holdover time,
especially in conditions of freezing precipitation. With this type of fluid additional
holdover time will be provided by increasing the concentration of fluid in the fluid/water
mix, with maximum holdover time available from undiluted fluid.

The tables 3, 4 and 5 hereafter give an indication of the time frame of protection that
could reasonably be expected under conditions of precipitation.
However, due to the many variables that can influence holdover times, these times
should not be considered as minimum or maximum as the actual time of
protection may be extended or reduced, depending upon the particular conditions
existing at the time.

The lower limit of the published time span is used to indicate the estimated time of
protection during heavy precipitation and the upper limit, the estimated time of
protection during light precipitation.

Caution

The times of protection represented in these tables are for general information
purposes only. They are taken from the ISO/SAE specification, however local
authority requirements may differ.
The time of protection will be shortened in severe weather conditions. Heavy
precipitation rates or high moisture content, high wind velocity and jet blast may
cause a degradation of the protective film. If these conditions occur, the time of
protection may be shortened considerably. This is also the case when the aircraft
skin temperature is significantly lower than the outside air temperature.

The indicated times should therefore only be used in conjunction with a pre-
takeoff check.

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Table 1 - Guideline for application of Type I fluid/water mixtures

One-step procedure Two-step procedure

OAT (°C) First step: Second step:

De-icing/anti-icing De-icing Anti-icing (**)

Water heated to 60°C

-3 and above minimum at the nozzle
Freezing point of heated or a heated mix of fluid Freezing point of
(*) fluid mixture shall be and water fluid mixture shall
at least 10°C below be at least 10°C
Freezing point of heated
actual OAT below actual OAT
Below - 3 fluid mixture shall not be
more than 3°C above
actual OAT

(*) Clean aircraft may be anti-iced with unheated fluid.

(**) To be applied before first step fluid freezes, typically within 3 minutes

Note: For heated fluids, a fluid temperature not less than 60°C at the nozzle is desirable. Upper
temperature limit shall not exceed 90°C or fluid manufacturer recommendations.

CAUTION: Wing skin temperatures may differ and in some cases may be lower than
OAT. A stronger mix (more glycol) can be used under the latter conditions

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Table 2 - Guideline for application of Type II and IV fluid mixtures.

Minimum concentrations as a function of OAT

Concentration fluid/water by volume (fluid % / water %)

One-step Two-step procedure

OAT (°C) procedure

De-/anti-icing First step: Second step:

de-icing anti-icing (**)

50/50 heated (*) Water heated to 60°C minimum at 50/50

-3 and above the nozzle or a heated mix of Type I,
Type II or IV II or IV with water Type II or IV

below -3 75/25 heated (*) 75/25

to -14 Type II or IV Heated suitable mix of Type I, II or Type II or IV
IV with freezing point not more than
below -14 100/0 heated (*) 3°C above actual OAT 100/0
to -25 Type II or IV Type II or IV
Type II / Type IV fluids may be used at temperatures below -25°C provided
below -25 that the freezing point of the fluid is at least 7°C below OAT and that
aerodynamic acceptance criteria are met. Consider the use of Type I fluid
when Type II or IV fluid cannot be used (see table 1).

(*) Clean aircraft may be anti-iced with unheated fluid.

(**) To be applied before first step fluid freezes, typically within 3 minutes

Note: For heated fluids, a fluid temperature not less than 60°C at the nozzle is desirable. Upper
temperature shall not exceed 90°C or fluid manufacturer recommendations.

CAUTION: Wing skin temperatures may differ and in some cases may be lower than OAT.
A stronger mix (more glycol) can be used under these conditions. As fluid
freezing may occur, 50% type II or IV fluid shall not be used for the anti-icing
step of a cold soaked wing.

CAUTION: An insufficient amount of anti-icing fluid, especially in the second step of a

two step procedure, may cause a substantial loss of holdover time. This is
particularly true when using a Type I fluid mixture for the first step (de-icing).

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Table 3 - Approximate holdover times achieved by Type I fluid mixtures

Approximate holdover times anticipated under various weather conditions

(hours:minutes)

OAT Frost Freezing Snow Freezing Light Rain on cold

(°C) (*) fog Drizzle Freezing soaked wings
(**) rain

above 0
0:45 0:12-0:30 0:06-0:15 0:05-0:08 0:02-0:05 0:02-0:05

0 to -10 0:45 0:06-0:15 0:06-0:15 0:05-0:08 0:02-0:05 ($)

Below -10 0:45 0:06-0:15 0:06-0:15

(*) During conditions that apply to aircraft protection for ACTIVE FROST (1)

(**) Use LIGHT FREEZING RAIN holdover times if positive identification of FREEZING
DRIZZLE is not possible

($) CAUTION: Clear ice may require touch for confirmation

CAUTION: For other weather conditions, i.e. snow pellets, snow grains, ice pellets,
moderate and heavy freezing rain, No holdover time guidelines exist

ISO/SAE Type I fluid / water mixture is selected so that freezing point of the mixture is at least 10°C
below actual OAT

CAUTION: ISO/SAE Type I fluids used during ground de-icing / anti-icing are not intended
for and do not provide ice protection during flight.

(1) "Active frost" means that the weather condition is such that frost is actually forming.
This in contradiction to the situation that frost has formed on an aircraft, for example, but at the
time of de-icing no frost is forming anymore, so in that case no protection for frost re-formation
is needed after the de-icing, which would be needed if the frost was still forming actively.
Active frost occurs when aircraft surface temperature is at or below 0°C and or below dew point.

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Table 4 - Approximate holdover times achieved by Type II fluid mixtures

Approximate holdover time anticipated under various weather

Type II fluid
conditions (hours:minutes)
mixture
concentration Freezing Snow Freezing Light Rain on
OAT
undiluted Frost fog Drizzle Freezing cold
(°C)
fluid/water (*) (***) rain soaked
(%Vol/%Vol) wings

100/0 12:00 1:05-2:15 0:20-1:00 0:30-1:00 0:15-0:30 0:05-0:40

above 0 75/25 6:00 0:50-1:45 0:15-0:40 0:20-0:45 0:10-0:25 0:05-0:25
50/50 4:00 0:15-0:35 0:05-0:15 0:05-0:20 0:05-0:10

100/0 8:00 0:35-1:30 0:20-0:45 0:30-1:00 0:15-0:30

0 to -3 75/25 5:00 0:25-1:00 0:15-0:30 0:20-0:45 0:10-0:25
50/50 3:00 0:15-0:35 0:05-0:15 0:05-0:20 0:05-0:10
($)

Below -3 100/0 8:00 0:30-1:05 0:15-0:35 0:15-0:45 0:10-0:30

to -14 75/25 5:00 0:20-0:55 0:15-0:25 0:15-0:30 0:10-0:20
(**) (**)
Below -14
100/0 8:00 0:15-0:20 0:15-0:30
to -25
ISO/SAE Type II fluids may be used below -25°C provided that the freezing
point of the fluid is at least 7°C below OAT and that aerodynamic
below -25 100/0 acceptance criteria are met. Consider the use of Type I fluid when Type II
fluid cannot be used (see table 3).

(*) During conditions that apply to aircraft protection for ACTIVE FROST (1)
(**) The lowest authorised temperature is limited to -10°C
(***) Use Light Freezing rain holdover times if positive identification of Freezing Drizzle is not
possible

($) CAUTION: Clear ice may require touch for confirmation

CAUTION: For other weather conditions, i.e. snow pellets, snow grains, ice pellets,
moderate and heavy freezing rain, No holdover time guidelines exist

CAUTION: ISO/SAE Type II fluids used during ground de-icing / anti-icing are not intended
for and do not provide ice protection during flight.

(1) "Active frost" means that the weather condition is such that frost is actually forming.
This in contradiction to the situation that frost has formed on an aircraft, for example, but at the
time of de-icing no frost is forming anymore, so in that case no protection for frost re-formation
is needed after the de-icing, which would be needed if the frost was still forming actively.
Active frost occurs when aircraft surface temperature is at or below 0°C and or below dew point.

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Table 5 - Approximate holdover times achieved by Type IV fluid mixtures

Approximate holdover time anticipated under various weather

Type IV fluid
conditions (hours:minutes)
mixture
concentration Frost Freezing Snow Freezing Light Rain on
OAT
undiluted fog Drizzle Freezing cold
(°C)
fluid/water (*) (**) rain soaked
(%Vol/%Vol) wings

100/0 18:00 1:05-2:15 0:35-1:05 0:40-1:00 0:25-0:40 0:10-0:50

above 0 75/25 6:00 1:05-1:45 0:20-0:40 0:30-1:00 0:15-0:30 0:05-0:35
50/50 4:00 0:20-0:35 0:05-0:20 0:10-0:20 0:05-0:10

100/0 12:00 1:05-2:15 0:30-0:55 0:40-1:00 0:25-0:40

0 to -3 75/25 5:00 1:05-1:45 0:20-0:35 0:30-1:00 0:15-0:30
50/50 3:00 0:20-0:35 0:05-0:15 0:10-0:20 0:05-0:10 ($)

100/0 12:00 0:40-1:30 0:20-0:40 0:20-0:55 0:10-0:30

Below -3
75/25 5:00 0:25-1:00 0:15-0:25 0:20-0:55 0:10-0:30
to -14
(**) (**)
Below -14
100/0 12:00 0:20-0:40 0:15-0:30
to -25
ISO/SAE Type IV fluids may be used below -25°C provided that the freezing
point of the fluid is at least 7°C below OAT and that aerodynamic
below -25 100/0 acceptance criteria are met. Consider the use of Type I fluid when Type IV
fluid cannot be used (see table 3).

(*) During conditions that apply to aircraft protection for ACTIVE FROST (1)
(**) The lowest authorised temperature is limited to -10°C
(***) Use Light Freezing rain holdover times if positive identification of Freezing Drizzle is not
possible

($) CAUTION: Clear ice may require touch for confirmation

CAUTION: For other weather conditions, i.e. snow pellets, snow grains, ice pellets,
moderate and heavy freezing rain, No holdover time guidelines exist

CAUTION: ISO/SAE Type IV fluids used during ground de-icing / anti-icing are not intended
for and do not provide ice protection during flight.

(1) "Active frost" means that the weather condition is such that frost is actually forming.
This in contradiction to the situation that frost has formed on an aircraft, for example, but at the
time of de-icing no frost is forming anymore, so in that case no protection for frost re-formation
is needed after the de-icing, which would be needed if the frost was still forming actively.
Active frost occurs when aircraft surface temperature is at or below 0°C and or below dew point.

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8.2.4.3.6. Pilot techniques

The purpose of this section is to deal with the issue of ground de-icing/anti-icing from
the pilot's point of view. The topic is covered in the order it appears on cockpit
checklists and is followed through, step by step, from flight preparation to take-off. The
focus is on the main points of decision-making, flight procedures and pilot techniques.

For additional information refer to FCOM:

- For A300 / A310 / A300-600:
Procedures and Techniques chapter - Inclement weather operations - Aircraft
preparation for cold weather operation.
- For A320 family / A330 / A340
Supplementary techniques chapter - Adverse weather - Cold weather

8.2.4.3.6.1. Receiving aircraft

When arriving at the aircraft, local advice from ground maintenance staff may be
considered because they may be more familiar with local weather conditions. If there is
nobody available or if there is any doubt about their knowledge concerning
de-icing/anti-icing aspects, pilots have to determine the need for de-icing/anti-icing by
themselves.

Checks for the need to de-ice/anti-ice are presented in section 8.2.4.3.3 and the
methods in section 8.2.4.3.5.
If the prevailing weather conditions call for protection during taxi, pilots should try to
determine «off block time» to be in a position to get sufficient anti-icing protection
regarding holdover time.
This message should be passed to the de-icing/anti-icing units, the ground
maintenance, the boarding staff, dispatch office and all other units involved.

8.2.4.3.6.2. Cockpit preparation

Before treatment, avoid pressurising or testing flight control systems.

Try to make sure that all flight support services are completed prior to treatment to
avoid any delay between treatment and start of taxiing.

During treatment observe that:

- engines are shut down or at idle
- APU may be used for electrical supply, bleed air OFF
- air conditioning should be OFF
- all external lights of treated areas must be OFF.

Consider whether communication and information with the ground staff is/has been
adequate.
A specific item included in the normal cockpit preparation procedures is recommended.

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The minimum requirement is to receive the anti-icing code in order to figure out the
available protection time from the holdover timetable.
Do not consider the information given in the holdover timetables as precise. There are
several parameters influencing holdover time.

The time frames given in the holdover timetables consider the very different weather
situations world-wide. The view of the weather is rather subjective; experience has
shown that a certain snowfall can be judged as light, medium or heavy by different
people. If in doubt, a pre-take-off check should be considered.

As soon as the treatment of the aircraft is completed, proceed to engine starting.

Regarding responsibility and decision, see section 8.2.4.3.4.

8.2.4.3.6.3. Taxiing

During taxiing, the flight crew should observe the intensity of precipitation and keep an
eye on the aircraft surfaces visible from the cockpit. Ice warning systems of engines
and wings or other additional ice warning systems must be considered.

Sufficient distance from the preceding aircraft must be maintained as blowing snow or
jetblasts can degrade the anti-icing protection of the aircraft.

The extension of slats and flaps should be delayed, especially when operating on
slushy areas. However, in this case slat/flap extension should be verified prior to
take-off.

8.2.4.3.6.4. Take-off

Recommendations given in FCOM of individual aircraft types regarding performance

corrections (effect of engine bleeds) or other procedures applied when operating in
icing conditions should be considered.

8.2.4.3.6.5. General remarks

In special situations flight crews must be encouraged not to allow operational or

commercial pressures to influence decisions. The minimum requirements have been
presented here, as well as the various precautions.

If there is any doubt as to whether the wing is contaminated - do not go on.

As in any other business, the key factors to keep procedures efficient and safe are
awareness, understanding and communication.
If there is any doubt or question at all, ground and flight crews must communicate with
each other.

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8.2.4.4. BACKGROUND INFORMATION

8.2.4.4.1. Aerodynamics and the contaminated wing

Aircraft designers do their best to ensure airframes have smooth surfaces to ease the
surrounding airflow. This rule is applied with special care to the wing leading edge and
upper surface, because smoothness in these areas produces the best lift force. Any
type of ice accretion is an obstacle to smooth airflow. Any obstacle will slow the airflow
down and introduce turbulence. That will degrade the lifting performance of the wing.
Figure 1 below gives the lift coefficient of a clean wing, and that of a wing spoiled by
ice.

LIFT C OE FF IC IE N T

C LE A N W IN G

IC E D W IN G

A N GLE OF AT TA CK

Figure 1 - Lift coefficient of a clean wing, and of a wing spoiled by ice

Both the maximum lift and the maximum achievable angle of attack have been
decreased. The mechanism by which lift is affected has to do with the evolution of the
boundary layer along the wing chord. Figure 2 below shows what happens at relatively
high angle of attack.

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Figure 2 - impact of ice accretion on aerodynamics

"

This set of sketches gives comparative explanation of the impact of ice accretion and
how these flight conditions are certified.
- Sketch ! is a reference: clean wing with normal boundary layer
- Sketch " is an iced wing in configuration zero. The ice accretion on the leading
edge is bigger than to scale. Aircraft is certified in those conditions because,
although the boundary layer is thicker, the aerodynamic "circulation" around the
wing is not severely affected. Lift is not highly affected, only flow separation,
therefore stall, occurs at a little lower angle of attack. Aircraft minimum operational
speeds take that maximum lift loss into account.
- Sketch # shows the same wing at landing conditions. In spite of the "pollution" of
the slat, the slat slot restores a "normal" boundary layer on the wing box. Again, the
"circulation" around the full wing is not severely affected and aircraft is certified to
land in those conditions.
- Sketch $ shows the result of morning frost after an overnight stay in clear sky
conditions. Even a very thin layer of velvet ice will destroy the boundary layer all on
the overwing. Result is a large decrease of "circulation". Lift loss may be large and
is not predictable. This is why these conditions are not certified.

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The boundary layer is thicker and more turbulent along the wing chord, and therefore,
flow separation will occur at a lower angle of attack. Stall speed will be increased. Note
how insidious that effect is, because at a moderate angle of attack, lift is about the
same, as seen in figure 1.

As it is not possible to take into account the whole possible variety of ice shapes,
Airbus has defined procedures based on the worst possible ice shapes, as tested in
flight with artificial ice shapes. As a consequence, in case of icing conditions, minimum
speeds are defined allowing keeping adequate margins in terms of manoeuvrability
relative to the actual stall with ice accretions. For example, when landing in
configuration FULL with ice shapes, speed must be above VREF+5 kt. However, for the
Airbus Fly-By-Wire system, the settings of the alpha protection system have been
adjusted with ice shapes. This means that the aircraft remains protected in case of
ice accretions. In turn, this means also that there is an increased margin relative to the
stall in the normal clean wing status.

In the case of ground icing, a similar result will be reached because the boundary
layer will thicken more rapidly along the chord. Earlier separation will occur, resulting in
lower max angle of attack and max lift. As a relatively high angle of attack is normally
reached during the takeoff rotation, it is easy to understand that wings must be
cleaned prior to takeoff.

Even the very thin layer of velvet morning frost must be cleared. Thickness may be
very small, but it covers 100% of the upperwing surface and the rate of thickening of
the boundary layer along the wing chord is still considerable. That is a threat for takeoff,
as nothing tells the pilot that he might not have the desirable lift for lift-off.

This also applies to the tailplane. Ice deposits must be cleared off tailplane before
takeoff to provide the expected rotation efficiency.

If the lower airframe structure has been extensively slushed during taxi time, it might be
advisable not to takeoff. The slush would freeze in flight, and an incident on landing
gear retraction might occur. Upon return to the gate, braking should be cautious and
slats and flaps should not be retracted prior to cleaning.

Frost initially forms as individual grains about 0.004 inch (0.1 mm) in diameter. Additional
build-up comes through grain growth to 0.010/0.015 inch (0.25/0.38 mm) in diameter,
grain layering, and the formation of frost needles.

Available test data indicate that a limited thickness of frost on the wing lower surface
will have no significant effect on lift. Airbus aircraft may be dispatched for flight with
slight amounts (less than 3 mm) of frost adhering to the fuel tank areas of wing
undersurfaces (Refer to FCOM).

During these conditions, clear ice will form on the upper side of the wing, especially if
there is cold fuel in contact with the upper wing skin.

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8.2.4.4.2. Fluid characteristics and handling

8.2.4.4.2.1. De-icing/anti-icing fluids - characteristics

Although numerous fluids are offered by several manufacturers worldwide, fluids can
be principally divided in two classes, Type I and Type II/IV fluids.

• Type I fluid characteristics

- No thickener system
- Minimum 80 percent glycol content
- Viscosity depends on temperature
- Newtonian fluid
- Relatively short holdover time

Depending on the respective specification, they contain at least 80 percent per volume
of either monoethylene-, diethylene- or monopropyleneglycol or a mixture of these
glycols. The rest comprises water, inhibitors and wetting agents. The inhibitors act to
restrict corrosion, to increase the flash point or to comply with other requirements
regarding materials' compatibility and handling. The wetting agents allow the fluid to
form a uniform film over the aircraft's surfaces.
Type I fluids show a relatively low viscosity which only changes depending on
temperature. Glycols can be well diluted with water.
The freezing point of a water/glycol mixture varies with the content of water, whereas
the concentrated glycol does not show the lowest freezing point; this is achieved with a
mixture of approximately 60 percent glycol and 40 percent water (freezing point below -
50°C). The freezing point of the concentrated monoethylene, diethylene or
propyleneglycol is in the range of -10°C.

Therefore Type I fluids are normally diluted with water of the same volume. This 50/50
mixture has a lower freezing point than the concentrated fluid and, due to the lower
viscosity, it flows off the wing much better.

• Type II/IV fluid characteristics

- With thickener system
- Minimum 50 percent glycol
- Viscosity depends on temperature and shear rates to which the fluid is exposed
- Pseudo-plastic or non Newtonian fluid
- Relatively long holdover time

Type II/IV fluids contain at least 50 percent per volume monoethylene-, diethylene- or
propyleneglycol, different inhibitors, wetting agents and a thickener system giving the
fluid a high viscosity. The rest is water.

Although the thickener content is less than one percent, it gives the fluid particular
properties. The viscosity of the fluid and the wetting agents causes the fluid to disperse
onto the sprayed aircraft surface, and acts like a protective cover.

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The fundamental idea is a lowering of the freezing point. Due to precipitation such as
snow, freezing rain or any other moisture, there is a dilution effect on the applied fluid.
This leads to a gradual increase of the freezing point until the diluted fluid layer is
frozen due to the low ambient temperature. By increasing the viscosity a higher film
thickness exists having a higher volume which can therefore absorb more water before
freezing point is reached. In this way the holdover time is increased.

The following summarises the properties of particular constituents of Type II and IV

fluids:
- The glycol in the fluid reduces the freezing point to negative ambient temperatures.
- The wetting agent allows the fluid to form a uniform film over the aircraft's surfaces.
- The thickening agent in Type II and IV fluids enables the film to remain on the
aircraft's surfaces for longer periods.

Type II and IV fluids can be diluted with water. Because of the lower glycol content,
compared to the Type I fluids, the freezing point rises all the time as water is added.
The viscosity of Type II and IV fluids is a function of the existing shear forces. Fluids
showing decreasing viscosity at increasing shear forces have pseudo-plastic or
non-Newtonian flow properties.

During aircraft take-off, shear forces emerge parallel to the airflow at the fluid and
aircraft surface. With increasing speed the viscosity decreases drastically and the fluid
flows off the wing.
The protective effect of the Type II and IV fluids is much better when compared to the
Type I fluids. Therefore they are most efficient when applied during snowfall, freezing
rain and/or with long taxiways before take-off.

Type II/IV and Type I fluids can all be diluted with water. This may be done if due to
weather conditions, no long conservation time is needed or higher freezing points are
sufficient.

All above types of fluid have to meet the specified anti-icing performance and
aerodynamic performance requirements as established in the respective specifications
(ISO, SAE, AEA). This has to be demonstrated by the fluid manufacturer.

8.2.4.4.2.2. Fluid handling

• General
De-icing/anti-icing fluids are chemical products with an environmental impact. During
fluid handling, avoid any unnecessary spillage, comply with local environmental and
health laws and the manufacturer's safety data sheet.
Mixing of products from different suppliers is generally not allowed and needs extra
qualification testing.
Slippery conditions due to the presence of fluid may exist on the ground or on
equipment following the de-icing/anti-icing procedure. Caution should be exercised due
to increased slipperiness, particularly under low humidity or non-precipitating weather
conditions.

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• Fluid handling equipment

The following information is generally valid for all types of fluid, but especially for Type
II and IV fluids.

As the structure of Type II and IV fluids is relatively complicated to comply with several
requirements, they are rather sensitive with regard to handling.
The holdover time, as one of the most important criteria, is gained essentially by
viscosity. The visco-elastic property of the fluid can be adversely affected by
overheating, mechanical shearing and contamination by corroded tanks in such a
manner that the expected and required holdover times cannot be achieved.

Therefore trucks, storage tanks and dressing plants have to be adequately conceived
and maintained to comply with these requirements.

Fluid shearing occurs when adjacent layers of fluid are caused to move relative to one
another, whether in opposite directions or in the same direction at different speeds.
This condition is unavoidable when pumping a fluid. For example, when merely moving
a fluid through a pipe, fluid velocity ranges from zero at the pipe wall to a maximum at
the centre. Type II and IV fluids are damaged when the magnitude of shear is sufficient
to break the long-polymer chains that make up the thickener. Therefore specific
equipment must be used.

• Storage
Tanks dedicated to storage of the de-icing/anti-icing fluid are required. The tanks
should be of a material of construction compatible with the de-icing/anti-icing fluid, as
specified by the fluid manufacturer. They should be conspicuously labelled to avoid
contamination.
Tanks should be inspected annually for corrosion and/or contamination. If corrosion or
contamination is evident, tanks should be maintained to standard or replaced. To
prevent corrosion at the liquid/vapour interface and in the vapour space, a high liquid
level in the tanks is recommended.

The storage temperature limits must comply with the manufacturer's guidelines. The
stored fluid shall be checked routinely to ensure that no degradation or contamination
has taken place.

• Pumping
De-icing/anti-icing fluids may show degradation caused by excessive mechanical
shearing. Therefore only compatible pumps as well as compatible spraying nozzles
should be used. The design of the pumping systems must be in accordance with the
fluid manufacturer's recommendations.

• Transfer lines
Dedicated transfer lines must be conspicuously labelled to prevent contamination and
must be compatible with the de-icing/anti-icing fluids to be transferred. An in-line filter,
constructed according to the fluid manufacturer's recommendations, is recommended
to remove any solid contaminant.

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• Heating
De-icing/anti-icing fluids must be heated according to the fluid manufacturer's
guidelines. The integrity of the fluid following heating in storage should be checked
periodically, by again referring to the fluid manufacturers guidelines. Such checks
should involve at least checking the refractive index and viscosity.

• Application
Application equipment shall be cleaned thoroughly before the first fill with
de-icing/anti-icing fluid in order to prevent fluid contamination. Fluid in trucks should not
be heated in confined or poorly ventilated areas such as hangars. The integrity
(viscosity) of the Type II and IV fluids at the spray nozzle should be checked annually,
preferably at the beginning of the winter season.

8.2.4.4.2.3. Environment and health

Besides water, de-icing/anti-icing fluids contain glycols and different additives as main
ingredients. Type II and IV fluids also contain a thickener system.
The glycols used are bivalent alcohols. Glycols are colourless fluids with a sweet taste
(not recommended to try).
Regarding environmental compatibility, the most important criteria are biodegradability
and toxicity.

• Biological degradation
The single glycols, like monoethylene, diethylene and propyleneglykol, are entirely
biodegradable. Biodegradable means that a conversion is achieved by aerobe bacteria
changing glycol to water and carbon dioxide by the aid of oxygen.
For the different glycols there are minor differences with regard to the rapidity of
biodegradation and the oxygen used. Also the temperature is an important parameter.
Biodegradation results faster at higher temperatures and slower at lower temperatures.

The best way to handle waste fluids is to drain them into local waste water treatment
plants. Fluids can be drained into surface waters during winter as the oxygen content
will be higher than during summer. The colder the water, the more oxygen is available.
Substantial drainage into surface waters during summer is not ideal as the
biodegradation occurs faster and, moreover, less oxygen is available. The overall effect
on surface waters can be adverse in such a case.
The glycols mentioned are practically non-toxic versus bacteria. Exceptionally high
amounts (10 to 20 grams per litre water) would be necessary to adversely affect the
biodegradation. These concentrations are effectively never reached, therefore
biodegradation generally does occur. Nevertheless, caution in this matter should be
exercised.
The thickener system of Type II and IV fluids, approximately one percent of volume of
the fluid, is totally neutral to the environment. It will not be degraded but has no
negative effects to the environment; it may be compared to a pebble.
The additives and inhibitors can have an effect on the overall biodegradability.
In any case, the fluids have to meet local regulations concerning biodegradability and
toxicity.

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• Toxicity
Although biodegradable, monoethylene-glycol should be considered as harmful if
swallowed. The principal toxic effects of ethylene glycol are kidney damage, in most
cases with fatal results.
Several reports concerning the toxicity of diethyleneglycol showed that it can be
compared to glycerine in this matter; glycerine is considered to be non-toxic.
Propyleneglycol is classified as non-toxic. A special pure quality is used in the
pharmaceutical, cosmetic, tobacco and beverages industry. Propyleneglycol is not
irritating and the conversion in the human body occurs via intermediate products of the
natural metabolism.
However, precautions generally usual in relation with chemicals should be considered
also when handling glycols.

• Protective clothes
Precautions include preventive skin protection by use of suitable skin ointment and
thick protective clothes as well as waterproof gloves.
Because of the possibility of atomisation, protective glasses should be worn. Soaked
clothes should be changed and, after each de-icing / anti-icing activity, the face and
hands should be washed with water.
Further details are available from the fluid manufacturers and the material data sheets
for their products.

8.2.4.4.2.4. De-anti/anti-icing equipment

• De-icing/anti-icing trucks
Most of the equipment used today are trucks consisting of a chassis on which the fluid
tanks, pumps, heating and lifting components are installed.
Although in older equipment centrifugal pumps are installed, more modern equipment is
fitted with cavity pumps or diaphragm pumps showing very low degradation of Type II
and IV fluids.
Most of the trucks have an open basket from which the operator de-ices/anti-ices the
aircraft. Closed cabins are also available, offering more comfort to the operator in a
severe environment.

• Stationary equipment
Stationary de-icing/anti-icing facilities, currently available at a limited number of
airports, consist of a gantry with spraying nozzles moving over the aircraft and similar in
concept to a car-wash.
The advantage of such a system is a fast and thorough treatment of the surface of the
aircraft. As these systems can be operated by computers, working errors are practically
excluded and consistent quality can be ensured.

The disadvantage, however, is the operational bottleneck. If only one system is

available and de/anti-icing is necessary, the take-off capacity of the respective runway
will be limited by the productivity of the gantry.

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