De-Icing & Anti-icing Fluids - Holdover Times

7/29/2019 De-Icing & Anti-icing Fluids - Holdover Times

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De-icing and Anti-icing fluids-

Holdover times

Operations Liaison Meeting


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2De-icing and Anti-icing fluids - Holdover times

Content

Clean aircraft concept De-icing / anti-icing fluids

Holdover times

Conclusion


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Clean aircraft concept

An aircraft ready for flight must not have ice,snow or frost adhering to its surfaces except as

authorized by the FCOM

A thin layer of hoarfrost is acceptable on theupper surface of the fuselage

A frost layer (due to cold fuel) not exceeding 3

mm is acceptable on the underside of the wing

as it will not penalize takeoff performance

Reminder


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Clean aircraft concept In winter conditions, de-icing and anti-icing

are the procedures used to prepare the aircraft

for takeoff in accordance with the clean aircraft

concept


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Clean aircraft concept

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 done by

mechanical methods application of heated de-icing fluids

Anti-icing is a precautionary procedure, which

provides protection against the formation of

frost, ice and snow accumulation on treatedsurfaces of the aircraft for a limited period of

timecalled holdovertime.

This is done by application ofanti-icing fluids

Definitions


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Content Clean aircraft concept

De-icing / anti-icing fluids

Holdover times

Conclusion


7/237De-icing and Anti-icing fluids - Holdover times


De-icing and anti-icing fluids are developed

and manufactured to industry standards

published by:

ISO (International Standard Organization)

SAE (Society of Automotive Engineers)

AEA (Association of European Airlines)

Fluids specification




De-icing / anti-icing fluids must:

Remove / prevent precipitation accumulation

on aircraft surface up to takeoff start Flow off the aircraft surface during takeoff so

as not to degrade takeoff performance

Requirements




The fluid which freezes at a very low temperature(e.g. -30C), is applied on a clean surface.

Process

It forms a protective layer.



De-icing / anti-icing fluids This fluid layer absorbs the frozen precipitation.

It keeps the freezing temperature of the diluted fluidwell below OAT or aircraft skin temperature, thus

preventing frozen precipitation to accumulate



De-icing / anti-icing fluids Then the layer becomes more and more diluted by the

melted precipitation; its freezing temperature increases When it reaches OAT or aircraft skin temperature, anti-

icing fluid fails and the frozen precipitation accumulates




Exceeding the holdover time means that theanti-icing fluid has failed and lost its

effectiveness, i.e. frozen precipitation is no

longer absorbed by the diluted anti-icing fluid,

making the protection ineffective.

The precipitation accumulates

Clean aircraft concept not fulfilled

Danger !!!




Type I fluids

Low viscosity

Viscosity reduces withtemperature

Limited holdover time

Blown off quickly Used mainly for de-icing

Type II, III, IV fluids

High viscosity (contain a

thickening agent)

Viscosity reduces with: shear force fluid concentration temperature

Longer holdover time

Blown off before rotation

Used for de-icing and anti-

icing

Different types of fluids



De-icing / anti-icing fluidsViscosity of Type II/IV fluids is greater than

viscosity of Type I fluids:Type II/IV fluids stick more on the aircraft surface

than Type I

Type II/IV fluid layer is thicker than Type I fluid layer

A greater volume of Type II/IV remains on aircraftsurface and can absorb more water before freezing

point reaches OAT or skin temperature

Undiluted Type II/IV fluids give maximum holdover

times while water/fluid ratio has no practical effect

on holdover time for Type I fluids

Type II/IV fluids have longer holdover times than

Type I



De-icing / anti-icing fluids As viscosity of Type II/IV fluids decreases with

increasing shear forces (increasing aircraft speed),they have been formulated to be blown off from

aircraft surface between 85 kt (Type II) and 100 to

110 kt (Type IV)

Both Type II and Type IV fluids are suitable for allAirbus aircraft which all have rotation speed above

110kt

Type IV fluids generally provide longer holdover

time than Type II Type I fluid are mainly used for de-icing

Note: Type III fluid are similar to Type II/IV fluids but are formulated to be

blown off during a low speed takeoff (used for turbo-propeller aircraft)





Holdover times

Conclusion



Holdover times Guidelines for application and for holdover times

achieved by various fluid mixtures are issued andpublished by various organizations (ISO, SAE or

AEA) and in the Aircraft Maintenance Manual

Holdover time begins at the start of the anti-icing

operation

Published holdover time charts are for

information only as protection period is affected

by multiple factors such as high wind velocity,aircraft skin temperature, jet blast, solar radiation

The indicated times should only be used

in conjunction with a pre-takeoff check


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Holdover timesExample of Type I fluid holdover times chart

(*)

(**) Use Light Freezing rain holdover times if positive identification of Freezing Drizzle is not possible

During conditions that apply to aircraft protection for ACTIVE FROST

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

- Short Holdover

times

- Not affected by

fluid

concentration

Estimated time of protection during

heavy-light precipitation

OAT

(C)

Approximate holdover time anticipated under various weatherconditions (hours:minutes)

Frost

(*)

Freezingfog

Snow FreezingDrizzle

(**)

LightFreezing

rain

Rain oncold

soakedwings

Above 0 0:45 0:12-0:030 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 0:30 0:06-0:15 0:06-0:15


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Holdover times

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

(**) The lowest authorized temperature is limited to -10C

(***) Use Light Freezing rain holdover times if positive identification of Freezing Drizzle is not possible

OAT

(C)

Type II fluidmixture

concentrationundiluted

Fluid / water

(%Vol / %Vol)

Approximate holdover time anticipated under various weather

conditions (hours:minutes)

Frost

(*)

Freezingfog


(***)

LightFreezing

rain

Rain oncold

soakedwings

above

0

100/075/25

50/50

12:006:00

4:00

1:15-3:000:50-2:00

0:20-0:45

0:20-1:000:15-0:40

0:05-0:15

0:30-1:000:20-0:45

0:10-0:20

0:15-0:300:10-0:25

0:05-0:10

0:10-0:400:05-0:25

0 to -3100/075/2550/50

8:005:003:00

0:35-1:300:25-1:000:15-0:45

0:20-0:450:15-0:300:05-0:15

0:30-1:000:20-0:450:10-0:20

0:15-0:300:10-0:250:05-0:10

below

-3 to

-14

100/0

75/25

8:00

5:00

0:35-1:30

0:25-1:00

0:15-0:40

0:15-0:25

0:25-1:00

0:20-0:45

(**)

0:10-0:30

0:10-0:25

(**)

below

-14 to

-25

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

below

- 25

100/0 ISO Type II fluids may be used below -25C provided that the freezing pointof the fluid is at least 7C below OAT and that aerodynamic acceptance criteriaare met. Consider the use of Type I fluid when Type II fluid cannot be used

Example of Type II fluid holdover times chart

- Longer

holdover times

which increasewith fluid

concentration


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Holdover times

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

(**) The lowest authorized temperature is limited to -10C

(***) Use Light Freezing rain holdover times if positive identification of Freezing Drizzle is not possible

OAT

(C)

Type II fluidmixture

concentrationundiluted

Fluid / water

(%Vol / %Vol)

Approximate holdover time anticipated under various weather

conditions (hours:minutes)

Frost

(*)

Freezingfog


(***)

LightFreezing

rain

Rain oncold

soakedwings

above

0

100/075/25

50/50

18:006:00

4:00

2:00-3:001:05-2:00

0:20-0:45

0:45-1:250:25-0:40

0:05-0:20

0:40-1:000:30-1:00

0:10-0:20

0:35-0:550:15-0:30

0:05-0:10

0:10-0:500:05-0:35

0 to -3100/075/2550/50

12:005:003:00

2:00-3:001:05-2:000:20-0:45

0:35-1:000:20-0:350:05-0:15

0:40-1:000:30-1:000:10-0:20

0:35-0:550:15-0:300:05-0:10

below

-3 to

-14

100/0

75/25

12:00

5:00

0:40-3:00

0:30-2:00

0:20-0:40

0:15-0:25

0:25-1:00

0:25-1:00

(**)

0:20-0:40

0:15-0:30

(**)

below

-14 to

-25

100/0 12:00 0:20-2:00 0:15-0:30

below

- 25

100/0 ISO Type IV fluids may be used below -25C provided that the freezing pointof the fluid is at least 7C below OAT and that aerodynamic acceptance criteriaare met. Consider the use of Type I fluid when Type II fluid cannot be used

Example of Type IV fluid holdover times chart

- Longer

holdover times

specially athigh fluid

concentration


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Holdover times Before departure under icing conditions or after a

de-icing / anti-icing operation, the aircraft mustreceive a final check by a responsible authorized

person

The flight crew must be notified the type of de-

icing / anti-icing operation performed including theanti-icing code to assess holdover time:

Type of

fluid used75% fluid /

25% waterLocal time at start

of last application

Ex: ISO Type II / 75 / 16.43 local PEK / 17 Nov 99

Date


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Holdover times

Conclusion


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23D i i d A ti i i fl id H ld ti

Conclusion Never underestimate the hazards of ice, snow or frost

Respect holdover times keeping in mind thatpublished data are affected by many factors

A check just prior to takeoff that the aircraft surfaces

are not contaminated is always necessary

Flight crew must be encouraged not to allowoperational or commercial pressure to influence

their decision

If there is any doubt as to whether the

aircraft is contaminated, do not go on

De-Icing & Anti-icing Fluids - Holdover Times

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