AIRCRAFT GROUND DEICING

WINTER AVIATION GUIDE

EDITION ONE REVISION B

ISSUED SEPTEMBER 2024

KILFROST WINTER AVIATION GUIDE 1

 Kilfrost Aircraft Ground Deicing Guides

Kilfrost Winter Aviation Guide

This guide describes the need for aircraft deicing fluids, their classification, the Kilfrost product range
and their care in use.

Kilfrost Winter Aviation Fluid Data Guide

This guide describes the technical detail associated with the Kilfrost product range.

KILFROST LTD
ALBION WORKS
HALTWHISTLE
NORTHUMBERLAND
NE49 0HJ
UK

(0) 1434 320

www.kilfrost.com

Disclaimer: All the information in this guide is for informational purposes only. Users should refer to their own local guidelines,
the airframe manufacturer’s guidance, statutory regulation, and other information before commencing operations. Kilfrost shall
not be held responsible for any damages resulting
KILFROST from any
WINTER error, inaccuracy
AVIATION GUIDE or omission contained in this publication 2
 THE KILFROST WINTER AVIATION GUIDE
1. An introduction to aviation and the effects of ice 4

2. The utility and classification of aircraft deicing and anti-icing fluids (ADF) 5

3. The Kilfrost ADF product range 6

3.1 Kilfrost Type I products 6

3.2 Kilfrost Type II and IV products 6
3.3 Kilfrost fluid technical data 6

4. Handling and storage of ADF products 7

4.1 Storage tanks 7

4.2 Pumps and transfer lines 7
4.3 Heating deicing fluids 7
4.4 Transitions to new ADF product use 8

5. Correctly obtaining a representative sample of fluid 9

5.1 Ensuring the quality of Kilfrost ADF products 9

5.2 Sampling from different storage sources 9

6. Sample requirements for submission to Kilfrost 10

6.1 Safety considerations while sampling ADF products 10

6.2 Sample containers and labelling requirements 10
6.3 How to label sample badly and attract delays 11
6.4 Kilfrost is here to help 11

7. Fluid quality testing and troubleshooting guides 12

7.1 Fluid acceptance at delivery 12

7.2 Heated storage periodic inspection 12
7.3 Vehicle checks periodic inspection 12
7.4 Periodic laboratory checks 12
7.5 Fluid troubleshooting guides 13

8. Field testing 14

8.1 Visual inspection 14

8.2 Refractive index 14
8.3 pH value measurement 14
8.4 Viscosity determination 15

9. Fluid application guidance 16

KILFROST WINTER AVIATION GUIDE 3

1. An introduction to aviation and the effects of ice
Any object can be made to fly with enough power and control. However, modern passenger aircraft are designed
to manage the forces acting on them as efficiently as possible, since there is estimated to be between half to one
million people travelling by air at any one moment. The smooth flow of air across the wings of an aircraft provides
the optimized lift and control necessary for modern flight. The continued refinement of these aerodynamic surfaces
has led to increasing efficiency and aviation safety improvements.

During winter operations, with the onset of freezing conditions, these efficiencies of lift and control are
compromised by the weight, roughness and unbalanced nature of the snow, ice, frost and slush that may be present
on the aircraft. For the same applied thrust, the extra weight, drag and loss of control may result in a much more
unstable and unpredictable aircraft. For these reasons, there is an industry-wide recognition of the need to remove
frozen contamination from an aircraft prior to allowing it to take off. For example, the International Civil Aviation
Organization (ICAO) Annex 6, Part I, and Annex 14, Vol. I, mandates specific rules for the safe operation of aircraft
during ground icing conditions, and all member states subsequently are required to have regulations in place to
ensure this. In part, these rules state:

4.3.5.6: A flight to be planned or expected to operate in suspected or known ground icing conditions shall not
take off unless the aircraft has been inspected for icing and, if necessary, has been given appropriate
deicing/anti-icing treatment. Accumulation of ice or other naturally occurring contaminants shall be removed
so that the aircraft is kept in an airworthy condition prior to take-off.

Any ice on the wings of an airplane leads to multiple detrimental effects:

• The aerofoil becomes rougher in nature, distressing the flow of air. A small accretion of ice can lower
the lift by between 30-50%, and can also increase the drag forces by between 100-200%1
• Aerodynamic penalties are a more severe hazard than the additional weight added to the airplane2
• If the ice is unevenly distributed, then the airplane can become more difficult to control3. If ice clumps
are shed, there may be impacts further down the plane.

The specific performance of any aircraft is determined and certified with the assumption that all of its aerodynamic
surfaces are clean. Any contamination will decrease this performance and control, a state of aerodynamics that has
not necessarily been assessed. The Clean Aircraft Concept must be very clear for a deicing ground crew. The motto
for winter operations is simple: “make it clean and keep it clean.”

1 Federal Aviation Administration (2006) “Pilot guide: flying in icing conditions” Advisory Circular AC 91-74.
2 M B Bragg, A P Broeren and L A Blumenthal (2005) “Iced-airfoil aerodynamics”, Progress in Aerospace Sciences, Volume 41, Issue 5, p. 323-362.
3 W J Baars, R O Stearman and C E Tinney (2010), “A review of the impact of icing on aircraft stability and control”.

KILFROST WINTER AVIATION GUIDE 4

2. The utility and classification of aircraft deicing and anti-icing fluids (ADF)
During winter operations with the onset of freezing conditions, the safe operation of aircraft can be maintained by
the use of deicing techniques. The purpose of these deicing techniques during winter is best described by the
concept of the “Clean Aircraft” which can simply be given as:
“To result in a performance as close to the original aerodynamics of the ice-free aircraft as the deicing
techniques will permit”
Principal amongst these deicing techniques is the use of deicing and anti-icing fluids. While there are a number of
techniques that may be used to deice aircraft (for example, use of infra-red warming), anti-icing (preventing the
formation of ice for a defined time period) can only be done using anti-icing fluids. Overall, the use of ADFs provides
both safety and versatility as:

• They are widely applicable to any aircraft type

• They are easy to deploy when the need arises
• There are good industry methods and practices

It should be remembered that these two fluid variations are designed for very different duties:

Deicing fluids: These are aqueous fluids which contain a glycol-based freeze point suppressant (usually
monopropylene glycol and sometimes ethylene glycol) and are sprayed onto aircraft to remove frozen
contamination without freezing themselves. Deicing fluids are normally supplied as a concentrate and diluted with
water by the end-user (to an appropriate freezing point, which is lower than the Outside Air Temperature (OAT)).
They are sprayed hot to assist in removal of ice and snow from the critical aircraft surfaces (especially the wing).
These are described as Type I fluids and are all dyed orange. After removal of frozen contamination, a thin film of
the deicing fluid remains on the aircraft which provides some protection against ice reforming, however the
duration of protection is limited, especially in active precipitation conditions.

Anti-icing fluids: After deicing an aircraft, anti-icing fluids can be applied to provide more substantial protection
from build-up of frozen contamination, especially when there is active precipitation. These are also aqueous glycol-
based fluids, however they also contain a thickening agent which increases viscosity and allows a thicker film of low
freeze point fluid to be applied to the aircraft. This thicker film provides protection from ice formation for extended
periods of time (Holdover Time, HOT). This property allows the aircraft to move from its embarkation point to the
runway without the danger of ice reforming. A further critical design requirement for anti-icing fluids is that they
should not interfere with the smooth flow of air over the wing surfaces during take-off and once airborne. To achieve
this, the thickening agent used conveys pseudoplastic/shear-thinning properties to the fluid. This means that the
fluid is more viscous when at rest (allowing a thicker film of fluid to remain on the aircraft after spraying), however
once subject to the shear stresses experienced during acceleration prior to take-off, the fluid structure breaks down,
the viscosity substantially decreases and the fluid flows off the aircraft. Therefore, anti-icing fluids have two distinct
performance criteria – to stay on the aircraft long enough to prevent ice reforming before take-off, and to flow off
the wing during take-off to leave a “clean aircraft”. Most commercial anti-icing products are designated as either
Type II (dyed yellow) or Type IV fluids (dyed green). Type II fluids were the first to arrive on the market, later
followed by Type IV fluids which were developed to provide extended performance in more extreme weather
conditions.

Type I: Orange Type II: Yellow Type IV: Green

KILFROST WINTER AVIATION GUIDE 5

Lowest Operational Use Temperature (LOUT)

Two important limits to safe operations with deicing and anti-icing fluids are:

(i) Adequate Freeze Protection

After application, taking into account the OAT and precipitation conditions, the freeze point of the fluid must remain
substantially lower than the outside air temperature prior to take off. Any fluid applied to an aircraft should have
a freezing point which is at least 10°C lower than the OAT in the case of deicing fluids and 7°C lower than the OAT
in the case of anti-icing fluids.
(ii) Effective Aerodynamic Performance
Both deicing fluids and anti-icing fluids undergo temperature-based aerodynamic evaluations when qualified to
AMS 1424 and 1428 standards. Fluids have a minimum temperature below which fluid flow-off characteristics start
to negatively interfere with an aircraft’s aerodynamic performance. The fluids can only be used in the field at
temperatures at or above which they have successfully passed the relevant aerodynamic acceptance test.

Taking into account both freeze point and aerodynamic limits of a specific deicing/anti-icing fluid, its Lowest
Operational Use Temperature (LOUT) is defined which is the higher of; (i) the lowest temperature at which it
meets the aerodynamic acceptance test, or; (ii) the freeze point of the fluid plus a buffer of 10°C (deicing fluids)
or the freeze point of the fluid plus 7°C (anti-icing fluids).

A fluid cannot be utilized at temperatures below its LOUT.

3. Kilfrost ADF product range

Kilfrost deicing and anti-icing products are based upon the freeze point depressant, 1,2-propylene glycol. This raw
material has a good chemical safety profile and is classified as GRAS (Generally Recognized as Safe). It is allowed in
many food and cosmetic products.

3.1 Kilfrost Type I products (SAE AMS1424/1 only)

Kilfrost Type I products are manufactured to the aviation industry standard SAE AMS 1424/14. They do not contain
any alkali organic salts such as formates or acetates.

Kilfrost DF Plus Triazole-free Type I deicing fluid

3.2 Kilfrost Type II and IV products (SAE AMS1428/1 only)

Kilfrost Type II and IV products are manufactured to the aviation industry standard SAE AMS 1428/15. They do not
contain any alkali organic salts such as formates or acetates.

Kilfrost ABC-K Plus Type II anti-icing fluid

Kilfrost ABC-S Plus Type IV anti-icing fluid (extended holdover protection)

3.3 Kilfrost fluid technical data

Technical data for the Kilfrost products are available in the “Kilfrost Winter Aviation Fluid Data Guide”, latest
edition.

4 Deicing/Anti-Icing Fluid, Aircraft SAE Type I Glycol (Conventional and Non-Conventional) Based
5 Fluid, Aircraft Deicing/Anti-Icing, Non-Newtonian (Pseudoplastic), SAE Types II, III, and IV Glycol (Conventional and Non-Conventional) Based

KILFROST WINTER AVIATION GUIDE 6

4. Handling and storage of ADF products
Correct handling and storage are of critical importance in order to ensure the satisfactory performance of de- and
anti-icing fluids. Incorrect storage or application of the fluid can result in adverse effects upon the final product
performance properties.

4.1 Storage tanks

Kilfrost fluids should not be exposed to any form of contamination or to direct sunlight. The preferred storage
temperature is between -20 to +30oC. A stock rotation policy should be adopted to ensure that fluid is not held
beyond its shelf life as listed in the individual product Certificates of Conformity. Tanks should be inspected annually
for any signs of corrosion or contamination. Suitable materials for the construction of storage tanks include:

• Stainless steel
• Mild steel, but only with a suitable lining e.g., epoxy-based coating
• Aluminium alloy for storage of cold fluid only
• Glass reinforced or molded plastic within their appropriate
temperature limitations

4.2 Pumps and transfer lines

Excessive mechanical shear can cause a decrease in the viscosity of

thickened (Type II and IV) fluids, which may negatively affect the holdover
values of these products. The recommended pump types for the transfer
and use of the anti-icing fluids are:

• Progressing cavity for multi-pass circulation

• Diaphragm for multi-pass or discharge pumping
• Centrifugal for single pass use only (extra caution required)

Transfer lines should be dedicated for each fluid and never used for different fluid types (Type I fluids are particularly
damaging to Type II and Type IV fluids). The lines should be clearly labelled and manufactured from glycol resistant
materials such as polypropylene (PP), polyethylene (PE) or polyvinylchloride (PVC). Transfer lines should be clean
and free from contaminants before use.

4.3 Heating deicing fluids

Heating can not only lead to the thermal degradation of the ADF products, but also to moisture loss by evaporation.
A reduction in pH, an increase in glycol content and discolouration are all signs of excessive thermal exposure.
Kilfrost ADF products can be satisfactorily warmed using heat exchangers powered by hot water, steam or oil. The
temperature of the heat exchange surfaces should not exceed a maximum of 120oC. For Type I products, the
temperature of the bulk fluid should not exceed 95oC for extended periods. For Type II and IV products, the
temperature of the fluids should not commonly exceed 70oC and should be inspected regularly. Direct exposure to
high surface temperature heating devices such as electric elements or flame heaters can seriously degrade the
products and should be avoided. In order to assist heat transfer and to avoid localized overheating, it is important
to circulate the fluids during warming. For thickened products, piping with 90o turns or T-stops may degrade the
fluid due to shear effects and should also be avoided.

KILFROST WINTER AVIATION GUIDE 7

 4.3.1 Standby heating

Although it is preferable to store all ADF products cold, during active icy weather it is advantageous to
store standby fluid warm. In such circumstances, fluids should be maintained at temperatures not exceeding
60oC and not for a period beyond 3 months. Do not unnecessarily heat fluids.

4.3.2 Heating for fluid application

Kilfrost ADF products are suitable for use in deicing operations at a

recommended maximum temperature of 70oC. Fluids should not be
maintained at these temperatures for periods exceeding 7 days for Type I, or
for 3 days for Type II or IV, as this may lead to significant fluid degradation.

4.4 Transitions to new ADF product use

The mixing or cross-contamination of different de- and anti-icing products can seriously affect the desired
performance properties and should never be done. It is therefore necessary that all storages and equipment
used are thoroughly cleaned during any fluid changeover.

4.4.1 Standard fluid changeover steps

• Drain the existing fluid from the entire system (if any fluid is being disposed, ensure that this is done in
accordance with local regulations)
• Flush all tanks, pipelines, valves and heaters with water which is warm or hot for best efficiency
• Confirm the absence of contamination, corrosion or fluid residues in the system, and that all water has drained
from system
• Fill the tank with some of the new fluid (not necessary to completely fill, however ensure that the base of the
tank has at least been completely covered), purge all lines. This rinses the new fluid into the system. Empty the
tank and dispose of the rinsing fluid (in accordance with local regulations).
• Add the new fluid to the tank, purge all lines again before collecting samples from all positions in the system
• Perform fluid checks to ensure the new fluid is within specification

4.4.2 Removal of any contamination during changeover

Kilfrost FL Solvent is an alkaline-based cleaning fluid used to remove residues and salt deposits that may
build up during winter operations. These residues can be broken down and flushed from the system using
a dilute solution of Kilfrost FL Solvent as follows:

• Drain the system and flush with water

• Fill the system with cold water and add enough FL Solvent to produce a 5% solution by weight
• Circulate the solution for 30 to 60 minutes and allow to stand for 24 hours
• Re-circulate for 5 to 10 minutes and drain the system
• Wash through twice with cold water
• Dispose of the used fluid according to local regulations

KILFROST WINTER AVIATION GUIDE 8

5. Correctly obtaining a representative sample of fluid
5.1 Ensuring the quality of Kilfrost ADF products
It is important to ensure that samples of ADF products are obtained in the correct manner and truly represent the
quality of the bulk fluid or reflect the effects of the application method. Due to the possible influence of vehicle or
equipment heating and delivery systems on fluid condition, it is necessary to assess the effect of how the fluid is
used for typical aircraft treatment. Kilfrost recommends that operators take samples of all static and vehicle fluid
storage tanks and from the nozzles of all de- and anti-icing vehicles for testing. This should be done at the start and
middle of the deicing season to ensure product integrity. End of season samples need not be done but may be done
when a deterioration of the product is suspected. Please note that samples taken for preseason and within-season
tests are in addition to requirements for daily concentration checks (please consult the latest revision of SAE AS6285
for further guidance). Ensure that any waste fluid generated through the sampling process is collected and disposed
in accordance with local regulations.

5.2 Sampling from different storage sources

The following steps are recommended for sampling from the appropriate storage sources:
5.2.1 Delivery truck
• Open the truck valve and drain a sufficient quantity of fluid to ensure the line has been well flushed
• Collect an additional amount of fluid as the representative sample
• Record the necessary details of the fluid and its source on a label before fixing this to the sample

5.2.2 Intermediate bulk container (IBC)

• Break the seal and open the IBC lid at the top
• If IBC has been sitting unused for long time, will be necessary to stir contents before taking a sample
• Lower the sample thief into the centre of the IBC
• Open the sample thief and allow it to fill completely
• Remove the sample thief and fill a clean, dry sample container from it
• Clean the outside of the sample container, and label appropriately
• Replace and tighten the IBC screw lid

5.2.3 Storage tank

• Access the storage tank via a top opening
• If storage tank fluid has been static for long duration, will be necessary to recirculate contents prior to sampling
• Lower the sample thief into the centre of the fluid
• Open the sample thief and allow it to fill completely
• Remove the sample thief and fill a clean, dry sample container from the thief
• Clean the outside of the sample container and label appropriately
• Close the top opening of the tank

5.2.4 Nozzle sample

The preferred method of sampling from a fluid application nozzle is to spray the product from about 3
metres away onto a purpose-built stand. The stand should consist of a suitable plate (which simulates the
aircraft surface) and a fluid collection system, usually a low point drain. In the absence of such a stand, the
fluid may be sprayed into a suitable clean receptacle, such as a new rubbish bin. In detail:
• Select the spray pattern and flow rate as required
• Spray a sufficient quantity of fluid in order to purge the lines
• Spray the fluid onto the plate from a distance of 3 metres perpendicular to the plate
• Collect enough fluid in order to retain a suitable sample
• Record the necessary fluid details on a label before fixing this to the sample

KILFROST WINTER AVIATION GUIDE 9

6. Sample requirements for submission to Kilfrost
6.1 Safety considerations while sampling ADF products

Prior to sampling any ADF product, the operator should be familiar with the appropriate Safety Data Sheet. It is
advisable for operators to use the following personal protective equipment when obtaining fluid samples:

• Safety glasses or a face shield

• Anti-slip boots
• Protective gloves, with insulation if a heated sample is to be taken

6.2 Sample containers and labelling requirements

All samples to be submitted to the Kilfrost laboratories must be clearly labelled and a full list compiled. Kilfrost
recommends the use of clean, dry sample containers of at least 500 and preferably 1,000 ml in size, with an opening
diameter of at least 50 mm. High density polyethylene or polypropylene bottles are preferred. Other types of
bottles, for example fizzy drink, glass or contaminated containers are NOT acceptable. Samples that DO NOT comply
with these simple requirements will not be tested and re-sampling may need to be done. The labels for all samples
must contain the following information and be securely attached to the container:

• Airport name and 3 letter code (for example, Heathrow LHR)

• Fluid type and concentration (e.g., Kilfrost ABC-S Plus, 100%)
• Sample origin (e.g., storage or vehicle tank)
• Sample date
• Refractive index
• pH value
• Contact details (Name and email)

Samples to be tested by Kilfrost should be sent to using the address below:

Technical Support Team

Kilfrost Limited
Albion Works
Haltwhistle
Northumberland
NE49 0HJ
UK
Telephone: +44 (0) 1434 320 332
Email: info@kilfrost.com

Note: before any samples are submitted to Kilfrost, the

Deicing Operator should carry out a Refractive Index check.
If the sample is outside the required limits for RI, the sample has
failed and immediate intervention is required to correct the RI
before continuing to use the fluid from this location and also before
obtaining a fresh sample to send to Kilfrost.

Please contact Kilfrost if guidance is required to adjust RI of a fluid.

KILFROST WINTER AVIATION GUIDE 10

6.3 How to label samples badly and attract many delays and resampling requests

The figure to the right gives examples of bad

sampling and labelling practice, including:

• No labels at all, or no description of the

contents, marker pen washed off
• No identifier of the airport, sample source or
the person to receive the report
• Samples of fluid that clearly smell of milk,
cola or lemonade due to poor selection of the
container for the fluid sample
• Samples not sealed correctly with a top
poorly closed and no sealing tape
• Containers are glass (break in transit) rather
than plastic
• Please do not follow these bad examples!

6.4 Kilfrost is here to help

Kilfrost offers comprehensive technical service to support our customers. For all requests for help and advice,
please do not hesitate to contact either:

Natalie Hewett Quality and Technical Service Manager natalie.hewett@kilfrost.com

+44 (0) 1434 323 150

Customer services General enquiries/orders customerservice@kilfrost.com

+44 (0) 1434 321 500

KILFROST WINTER AVIATION GUIDE 11

7. Fluid quality testing and troubleshooting guides
7.1 Fluid acceptance at delivery

The following steps are recommended for the receipt of an ADF product:

• Check that the fluid corresponds to the product ordered

• Check that the delivery documents correspond to the fluid delivered
• Check that the delivered fluid corresponds to the appropriate storage tank designation
• Prior to the transfer of the delivered fluid, a sample should be obtained, and the following checks carried out:
visual appearance, refractive index value, pH and viscosity (viscosity for Type II and IV only). The results should be
documented by the receiving party

7.2 Heated storage periodic inspection

Where fluid is stored at elevated temperatures for prolonged periods, the following checks should be performed at
intervals not exceeding 2 weeks:

• Visual inspection, refractive index value, pH and viscosity (viscosity check is for Type II and IV only)

7.3 Vehicle checks periodic inspection

Daily (when in use) refractive index checks shall be performed on fluid samples obtained from a manufacturers’
authorized sampling point, or alternatively nozzle, for each vehicle used in deicing. Please consult latest edition of
SAE AS6285 for further guidance.

7.4 Periodic laboratory checks

Laboratory checks should be performed at the start (preseason) and middle of the deicing season (within-season).
They may also be performed at the end of the season, or if there is any reason to suspect any concerns of fluid
quality at any other time. Fluid should be taken from all storage and vehicle tanks, in addition to nozzle spray
samples, and checked by visual inspection, refractive index value, pH and viscosity measurements (viscosity for Type
II and IV only).

KILFROST WINTER AVIATION GUIDE 12

7.5 Fluid troubleshooting guides

The following guides give an overview of types of potential fluid problems and suggested actions for resolving issues.

Visual Inspection Troubleshooting

Issue Potential cause Preventative measure

(i) Fluid degradation by high temperature (i) Reduce temperature when not in use
Discolouration
(ii) Fluid contamination (ii) Regular inspection of tanks, rigs, pumps and nozzles
(i) Rubber particles (i) Regular inspection of hoses and seals for degradation
Contamination (ii) Metal/rust particles (ii) Inspection of tanks, pumps and nozzles for corrosion
(iii) Flakes/particles of paint/resin/coating (iii) Inspection of tanks for coating delamination/failure
Separation Keep fluid within recommended temperature storage range (-
Overexposure to very cold temperatures
(Type II / IV) 20oC to +30oC)

Refractive Index (RI) Troubleshooting

Issue Potential cause Preventative measure

Ensure fluid is well mixed and sample from the centre of the
Sampling from the upper layer of the fluid in tanks
Low tank
Refractive Sampling from nozzles, and transfer lines
Index Purge fluid through the transfer lines prior to taking a sample
contaminated with water
Low glycol to water ratio Investigate and prevent water ingress into the fluid

Ensure fluid is thoroughly mixed and sample from the centre of

High Sampling from the lower layer of the fluid in the tank
the tank
Refractive
Index Reduce fluid temperature when not in use to prevent the
High glycol to water ratio
evaporation of water

pH Troubleshooting

Issue Potential cause Preventative measure

Fluid degradation due to elevated temperatures Reduce fluid temperature when not in use
Low
pH Regular inspection of storage tanks, rigs, pumps and nozzles to
Fluid contamination by foreign materials or rust
reduce incidence of degradation or corrosion

Viscosity Troubleshooting (Type II / IV fluids only)

Issue Potential cause Preventative measure

Fluid degradation through excessive shear by pumps Minimise fluid shear using the recommended pumps, correct
Low or nozzles nozzle settings and lower rig pressures
Viscosity
Fluids Fluid may be contaminated by foreign particles or Regular inspection of storage tanks, rigs, pumps and nozzles to
rust reduce incidence of degradation or corrosion
Overheating fluid Reduce fluid temperature when not in use

Fluid is kept static for a long period of time Mix the fluid on a regular basis to ensure consistency
High
Ensure the fluid is thoroughly mixed and sample from the
Viscosity Incorrect sampling from the lower layer of a tank
centre of the tank
Fluids
Overheating fluid Reduce fluid temperature when not in use

KILFROST WINTER AVIATION GUIDE 13

8. Field testing
Field tests are designed to provide a fast and simple analysis of ADF products. If there is any doubt about the
results of such tests or quality of fluid in the field, then samples can be submitted to the Kilfrost laboratories for
analysis and advice, at any time.

8.1 Visual inspection

Using a transparent container, visually check the fluid sample for signs of discolouration or contaminants. All
Kilfrost fluids should be clear, homogenous and free from particulates.

8.2 Refractive index

Refractive index (RI) measurements permit a simple determination of the glycol level, and hence freeze-point, of
any fluid mixture. The glycol concentration is directly related to the mix ratio and the freezing point of the fluid. RI
measurements can be made using hand-held field refractometers as described below. Alternatively, digital
refractometers can be used according to the manufacturer’s guidelines. Please note - refractive index is a
temperature dependent property.

Equipment required: field refractometer, plastic pipettes, tissue paper

Check the instrument calibration:

• Lift the cover flap and wipe the prism with a tissue to ensure that clean and dry
• Place a few drops of water on the prism (instrument and fluid should be at 20 C for correct measurements)
• Close the flap, hold the instrument up to the light and look through the eyepiece
• Rotate the eyepiece to focus the scale
• The RI is the reading at the borderline position between the light and dark areas
• Check that the RI reads as 1.333 (+/- 0.002)

Measuring the Refractive Index:

• Lift the cover flap and wipe the prism with a tissue to ensure that clean and dry
• Place a few drops of sample onto the prism (instrument and fluid should be at 20 C for correct measurements)
• Close the flap, hold the instrument up to the light and look through the eyepiece
• Rotate the eyepiece to focus the scale
• The RI is the reading at the borderline position between the light and dark areas
• Refer to the Kilfrost RI Freezing Point Chart for the fluid being used (see Kilfrost Winter Aviation Fluid Data
Guide) in order to determine the concentration and hence the freezing point of the fluid
• Thoroughly clean the prism after use with water and clean with a dry tissue

8.3 pH value measurement

The pH value of Kilfrost ADF products can be used to indicate fluid degradation. See product specifications in
Kilfrost Winter Aviation Fluid Data Guide. Portable pH meters can provide accurate readings in the field, however
these instruments require careful and frequent maintenance to ensure that measurements are accurate (fluid
needs to be at 20 C for pH measurements). Please consult Kilfrost for further guidance.

KILFROST WINTER AVIATION GUIDE 14

8.4 Viscosity determination

The viscosity of Type II and IV fluids is critical to their performance in use. Brookfield rotational viscometers are
used for the most accurate viscosity measurements in formal Kilfrost quality control tests. Alternatively, Kilfrost
use flow cup viscometers in a simple viscosity field test to ensure that anti-icing fluids are within the correct viscosity
range in the field. The viscosity is expressed in seconds of flow time as it leaves the orifice of the flow cup at a
specific temperature (viscosity measurements are highly temperature dependent). Please refer to the Kilfrost
Winter Aviation Fluid Data Guide for product-specific flow cup data/limits and also Brookfield viscosity limits for
thickened fluids.

Kilfrost Flow Cup Viscometer Test Method

Equipment required: Kilfrost flow cup, sample container, thermometer, stopwatch, flow cup chart

• Ensure the flow cup is clean, dry and contamination-free prior to use
• Pour a minimum of 400 ml of fluid into a container with an opening not less than 50 mm
• Immerse the cup in the fluid and leave for around 1 minute in order to reach thermal equilibrium
• Determine the temperature of the fluid using the thermometer
• Raise the cup vertically out of the fluid in a quick and steady motion. As the top edge of the cup breaks the surface of the
fluid, start the stopwatch
• During the time the liquid flows out of the cup, hold it no more than 15 cm from the fluid surface
• Stop the stopwatch when the continuous flow of fluid from the bottom of the cup breaks down
• Record time taken, and repeat the measurement 2 further times. Determine the average of the 3 measurements
• Compare the average flow time against the product-specific limits/data provided in the Kilfrost Winter Aviation Fluid Data
Guide to verify whether the fluid is meeting viscosity specification

Helpful hints

• Check that the flow cup has fully drained at the end of each measurement. If fluid remains in the cup, this measurement
should be disregarded, and the instrument cleaned and thoroughly dried prior to repeating measurement.
• Use cold water to clean the viscometer (use moderately hot water if necessary)
• Dry the viscometer thoroughly after use to prolong its lifetime
• Heavily aerated fluids may give artificially high flow times
• Never use metal tools in contact with the flow cups. Any damage caused to the cup orifice can seriously affect the
accuracy of the results
• If there is any doubt about the accuracy of any viscosity measurement, the final decision on its acceptability should
always be based on a Brookfield viscometer reading.

KILFROST WINTER AVIATION GUIDE 15

9. Fluid application guidance
Aircraft deicing fluids are supplied in concentrate form, from which dilute solutions can be made. As previously
mentioned, the two main fluid variations have different duties, although dilutions can be made to enhance the
versatility of these basic variants.
Deicing Type I fluids: These are typically supplied as a concentrate (high glycol content of 80% and above) and must be diluted with water
to their maximum usable concentration or lower before use (consult Kilfrost Winter Aviation Fluid Data Guide). The chosen dilution at a
specific temperature shall always ensure that the freeze point of the fluid (+10 oC buffer) is below the Outside Air Temperature, while also
respecting the aerodynamic LOUT of the fluid (see Section 2). Spraying of these hot, dilute solutions at around 60oC removes frost, ice and
snow from the wing surfaces. Deicing performance results from a combination of the freeze-point suppression (provided by the glycol),
together with the thermal energy (transferred from the hot fluid) and also the physical pressure from the spraying process.

Anti-icing Type II and IV fluids: These are supplied as products with about 50% content of glycol. Due to the technology used in thickening
the mixtures, and glycol content, holdover time can be maximized if the fluid is used as received. If weather conditions (temperature and
precipitation) allow, for economy the fluid can be diluted to standard levels (down to 75% or 50%, as supplied, with water) to provide lower
levels of holdover time and higher freeze point, as required. Again, the fluid used at a specific Outside Air Temperature (OAT) shall always
have a freeze point (+7oC buffer) which is lower than the OAT, while also ensuring that the OAT is not lower than the aerodynamic LOUT of
the fluid at the concentration used.

Dilutions should be carried out with clean mains water. For thickened fluids, heating the water to about 60 oC can aid the
thorough mixing process necessary to obtain a homogenous final product. Consistent product can be demonstrated by
consistent refractive index readings of the fluid from different samples and different sampling points. The use of hard water for
dilutions is known to have a negative effect on the performance of de- and anti-icing fluids. If there is any doubt about water
suitability, a sample can be provided to the Kilfrost laboratory for analysis.

The deicing process

The received Type I fluid is diluted to a required freeze point, heated, and sprayed over
the permitted sprayable surfaces of the aircraft (avoiding no spray areas). Airframe
manufacturers publish guidance on the best methods to use, and much assistance is
available from bodies such as the SAE through publications such as AS6285. The key
deicing principle is to dilute the Type I product down to where the freeze point of the
resultant fluid remains well below the outside air temperature (OAT) through
incorporation of a +10oC buffer, while respecting the aerodynamic LOUT of the fluid.
The higher of the freeze point of the fluid (+ buffer) and the aerodynamic LOUT of the
fluid, gives a lowest operational use temperature (LOUT) for any fluid dilution. The fluid
application temperature should be around 60oC at the nozzle. However, any holding
tanks on the deicing equipment should not exceed a temperature of 70-80oC.

Removal of frost: Set nozzle to a fan spray, use a medium flow rate and
spray over all frozen surfaces while keeping close to
the aircraft skin

Removal of ice: Direct a jet onto the ice and expose a bare surface,
then work outwards from this point flushing away the
ice with low or high flow as required

Removal of snow: For light deposits, use a medium flow rate with a
coarse spray to give a large droplet pattern. For wet
snow, a high flow rate is more effective, combined
with the force of the fluid being applied

KILFROST WINTER AVIATION GUIDE 16

The anti-icing process

For anti-icing, the key requirement is the holdover time desired for the prevailing weather conditions on the airfield.
The nominal concentrations of Type II and Type IV fluid that are used are 100, 75 and 50%. Each concentration of
commercial products has been tested and certified through industry holdover tables to give a good indication of the
available time to prevent re-icing at the appropriate dilution. These holdover times are valid whether the fluid is
applied either heated or cold. The freezing point of the anti-icing fluid used should comply with the freezing point
buffer for thickened fluids (should be at least 7oC below the Outside Air Temperature (OAT) and aerodynamic
acceptability of the fluid dilution (LOUT)).

Use of anti-icing fluid:

Select the fluid type and concentration to suit prevailing weather conditions. After the aircraft has been deiced,
apply an even and continuous coating of the anti-icing fluid to the required surfaces of the aircraft. Sufficient fluid
has been applied when it has completely purged these surfaces e.g. dripping from the leading and trailing edges of
the wings.

Two-step and one-step aircraft deicing:

The deicing and anti-icing processes described above produce a “clean aircraft” by firstly removing the ice and snow,
and then consolidating this with anti-icing treatment to give an extended window of ice-free time. This allows the
aircraft to move to their take-off point and depart safely. This procedure is called a two-step de- and anti-icing
process. In order to do this two-step process, the second step shall be performed before the first step fluid freezes,
if necessary, area by area.

It is also possible to operate a one-step process, whereby a heated anti-icing fluid is used to effect de- and anti-icing
with one fluid.

In addition to the above general ways of operating, the two-step process has the added feature that any residues
from the thickened anti-icing fluids from previous treatments are removed during the first step application of
diluted Type I fluid using heat and spray techniques. Such thickened fluid residues have been found in some
instances to build up and affect critical control areas of the aircraft.

Holdover times and Holdover Tables

The SAE Types of fluid are defined by their holdover times under laboratory conditions (described in the SAE
publications AMS1424 (TI) and 1428 (TII and TIV)). While these very controlled conditions allow a simple comparison
evaluation and categorization to be carried out, real weather conditions (ice, snow, hail, frost) mean that holdover
times vary greatly for different fluids in the field.

Holdover Tables have been developed to fill this need, particularly for thickened products (Type I products typically
all use the same generic Holdover Table). These tables list the different commercial products and their expected
holdover times under different weather conditions for the different standard dilutions (100, 75 and 50% for Type II
and Type IV). They are published annually by bodies such as the US Federal Aviation Authority (FAA) and Transport
Canada (TC) and are used by aircraft pilots as guidance to assess the holdover time windows of safety which they
can feel confident will apply during actual winter weather events.

KILFROST WINTER AVIATION GUIDE 17

Global leaders in deicing and anti-icing

Albion Works, Haltwhistle, Northumberland, NE49 0HJ, UK

Telephone: +44 (0) 1434 320 332
www.kilfrost.com

Date of issue: September 2024

© Kilfrost Ltd

THE KILFROST WINTER AVIATION GOOD FLUID GUIDE 18