NCC.OP.185 Ice and other contaminants – ground procedures

TERMINOLOGY Terms used in the context of de-icing/anti-icing have the meaning defined in the following subparagraphs.

(a)‘Anti-icing’: the process of protecting the aircraft to prevent contamination due to existing or expected weather, typically by applying anti-icing fluids on uncontaminated aircraft surfaces.

(b)‘Anti-icing fluid’ includes, but is not limited to, the following:

(1)Typically, Type II, III or IV fluid (neat or diluted), normally applied unheated (*);

(2)Type I fluid/water mixture heated to minimum 60°C at the nozzle. (*) When de-icing and anti-icing in a one-step process, Type II and Type IV fluids are typically applied diluted and heated.

(c)‘Clear ice’: a coating of ice, generally clear and smooth, but with some air pockets. It forms on exposed objects, the temperatures of which are at, below or slightly above the freezing temperature, by the freezing of super-cooled drizzle, droplets or raindrops. Clear ice is very difficult to be detected visually.

(d)‘Cold soaked surface frost (CSSF)’: frost developed on cold soaked aircraft surfaces by sublimation of air humidity. This effect can take place at ambient temperatures above 0 °C. Cold soaked aircraft surfaces are more common on aircraft that have recently landed. External surfaces of fuel tanks (e.g. wing skins) are typical areas of CSSF formation (known in this case as cold soaked fuel frost (CSFF)), due to the thermal inertia of very cold fuel that remains on the tanks after landing.

(e)‘Conditions conducive to aircraft icing on the ground’: freezing fog, freezing precipitation, frost, rain or high humidity (on cold soaked wings), hail, ice pellets, snow or mixed rain and snow.

(f)‘Contamination’: all forms of frozen or semi-frozen deposits on an aircraft, such as frost, snow, slush or ice.

(g)‘Contamination check’: a check of the aircraft for contamination to establish the need for de-icing.

(h)‘De-icing’: the process of eliminating frozen contamination from aircraft surfaces, typically by applying de-icing fluids.

(i)‘De-icing fluid’: such fluid includes, but is not limited to, the following:

(1)Heated water;

(2)Preferably, Type I fluid (neat or diluted (typically));

(3)Type II, III or IV fluid (neat or diluted). The de-icing fluid is normally applied heated to ensure maximum efficiency and its freezing point should be at the outside air temperature (OAT) or below.

(j)‘De-icing/anti-icing’: this is the combination of de-icing and anti-icing performed in either one or two steps.

(k)‘Ground ice detection system (GIDS)’: a system used during aircraft ground operations to inform the personnel involved in the operation and/or the flight crew about the presence of frost, ice, snow or slush on the aircraft surfaces.

(l)‘Holdover time (HOT)’: the period of time during which an anti-icing fluid provides protection against frozen contamination to the treated aircraft surfaces. It depends among other variables, on the type and intensity of the precipitation, OAT, wind, the particular fluid (or fluid Type) and aircraft design and aircraft configuration during the treatment.

(m)‘Liquid water equivalent (LWE) system’: an automated weather measurement system that determines the LWE precipitation rate in conditions of frozen or freezing precipitation. The system provides flight crew with continuously updated information on the fluid protection capability under varying weather conditions.

(n)‘Lowest operational use temperature (LOUT)’: the lowest temperature at which a fluid has been tested and certified as acceptable in accordance with the appropriate aerodynamic acceptance test whilst still maintaining a freezing point buffer of not less than:

(1)10°C for a Type I fluid; or

(2)7°C for Type II, III or IV fluids.

(o)‘Post-treatment check’, ‘Post- de-icing check’ or ‘Post- de-icing/anti-icing check’: an external check of the aircraft after de-icing and/or anti-icing treatment accomplished by qualified staff and from suitably elevated observation points (e.g. from the de-icing/anti-icing equipment itself or other elevated equipment) to ensure that the aircraft is free from frost, ice, snow, or slush.

(p)‘Pre-take-off check’: The flight crew should continuously monitor the weather conditions after the de-icing/anti-icing treatment to assess whether the applied holdover time is still appropriate. Within the aircraft’s HOT and prior to take-off, the flight crew should check the aircraft’s wings or representative aircraft surfaces for frozen contaminants.

(q)‘Pre-take-off contamination check’: a check of the treated surfaces for contamination, performed when the HOT has been exceeded or if any doubt exists regarding the continued effectiveness of the applied anti-icing treatment. It is normally accomplished externally, just before commencement of the take-off run.

ANTI-ICING CODES

(r)Upon completion of the anti-icing treatment, a qualified staff provides the anti-icing code to the flight crew as follows: ‘the fluid Type/the fluid name (except for Type I)/concentration (except for Type I)/local time at start of anti-icing/date (optional)/the statement ‘post- de-icing/anti-icing check completed’ (if check completed). Example: ‘TYPE II / MANUFACTURER, BRAND X / 75% / 1335 / 15FEB20 / POST- DE-ICING/ANTI-ICING CHECK COMPLETED’.

(s)When a two-step de-icing/anti-icing operation has been carried out, the anti-icing code should be determined by the second step fluid.

DE-ICING/ANTI-ICING — PROCEDURES

(a)De-icing and/or anti-icing procedures should take into account manufacturer’s recommendations, including those that are type-specific, and should cover:

(1)contamination checks, including detection of clear ice and under-wing frost; limits on the thickness/area of contamination published in the AFM or other manufacturers’ documentation should be followed;

(2)procedures to be followed if de-icing and/or anti-icing procedures are interrupted or unsuccessful;

(3)post-treatment checks;

(4)pre-take-off checks;

(5)pre-take-off contamination checks;

(6)the recording of any incidents relating to de-icing and/or anti-icing; and

(7)the responsibilities of all personnel involved in de-icing and/or anti-icing.

(b)The operator’s procedures should ensure the following:

(1)When aircraft surfaces are contaminated by ice, frost, slush or snow, they are de-iced prior to take-off, according to the prevailing conditions. Removal of contaminants may be performed with mechanical tools, fluids (including hot water), infrared heat or forced air, taking account of aircraft type-specific provisions.

(2)Account is taken of the wing skin temperature versus OAT, as this may affect:

(i)the need to carry out aircraft de-icing and/or anti-icing; and/or

(ii)the performance of the de-icing/anti-icing fluids.

(3)When freezing precipitation occurs or there is a risk of freezing precipitation occurring that would contaminate the surfaces at the time of take-off, aircraft surfaces should be anti-iced. Anti-icing fluids (neat or diluted) should not be applied at OAT below their LOUT. If both de-icing and anti-icing are required, the procedure may be performed in a one- or two-step process, depending upon weather conditions, available equipment, available fluids and the desired HOT. One-step de-icing/anti-icing means that de-icing and anti-icing are carried out at the same time, using a mixture of de-icing/anti-icing fluid and water. Two-step de-icing/anti-icing means that de-icing and anti-icing are carried out in two separate steps. The aircraft is first de-iced using heated water only or a heated mixture of de-icing/anti-icing fluid and water. After completion of the de-icing operation, a layer of a mixture of de-icing/anti-icing fluid and water, or of de-icing /anti-icing fluid only, is sprayed over the aircraft surfaces. The second step will be taken before the first step fluid freezes (typically within 3 minutes but severe conditions may shorten this) and, if necessary, area by area.

(4)When an aircraft is anti-iced and a longer HOT is needed/desired, the use of a less diluted thickened fluid may be considered.

(5)All restrictions relative to OAT and fluid application (including, but not necessarily limited to, temperature and pressure) published by the fluid manufacturer and/or aircraft manufacturer, are followed and procedures, limitations and recommendations to prevent the formation of fluid residues are followed.

(6)During conditions conducive to aircraft icing on the ground or after de-icing and/or anti-icing, an aircraft is not dispatched for departure unless it has been given a contamination check or a post-treatment check by a trained and qualified person. This check should cover all treated surfaces of the aircraft and be performed from points offering sufficient visibility to these parts. To ensure that there is no clear ice on suspect areas, it may also be necessary to make a physical check (e.g. tactile).

(7)The required entry is made in the technical log.

(8)The commander continually monitors the environmental situation after the performed treatment. Prior to take-off, he/she performs a pre-take-off check, which is an assessment of whether the applied HOT is still appropriate. This pre-take-off check includes, but is not limited to, factors such as precipitation, wind and OAT.

(9)If any doubt exists as to whether a deposit may adversely affect the aircraft’s performance and/or controllability characteristics, the commander should arrange for a re-treatment or a pre-take-off contamination check to be performed in order to verify that the aircraft’s surfaces are free of contamination. Special methods and/or equipment may be necessary to perform this check, especially at nighttime or in extremely adverse weather conditions. If this check cannot be performed just before take-off, re-treatment should be applied.

(10)When retreatment is necessary, any residue of the previous treatment should be removed, and a completely new de-icing/anti-icing treatment should be applied.

(11)When a ground ice detection system (GIDS) is used to perform an aircraft surfaces check prior to and/or after a treatment, the use of GIDS by suitably trained personnel should be part of the procedure.

(c)Special operational considerations

(1)When using thickened de-icing/anti-icing fluids, the operator should consider a two-step de-icing/anti-icing procedure, the first step preferably with hot water and/or un-thickened fluids.

(2)The use of de-icing/anti-icing fluids should be in accordance with the aircraft manufacturer’s documentation. This is particularly important for thickened fluids to assure sufficient flow-off during take-off. Avoid applying excessive thickened fluid on the horizontal tail of aircraft with unpowered elevator controls.

(3)The operator should comply with any type-specific operational requirement(s), such as an aircraft mass decrease and/or a take-off speed increase associated with a fluid application.

(4)The operator should take into account any flight handling procedures (stick force, rotation speed and rate, take-off speed, aircraft attitude, etc.) laid down by the aircraft manufacturer when associated with a fluid application.

(5)The limitations or handling procedures resulting from (c)(3) and/or (c)(4) should be part of the flight crew pre-take-off briefing.

(d)Communications

(1)Before aircraft treatment. When the aircraft is to be treated with the flight crew on board, the flight and personnel involved in the operation should confirm the fluid to be used, the extent of treatment required and any aircraft type-specific procedure(s) to be used. Any other information needed to apply the HOT tables should be exchanged.

(2)Anti-icing code. The operator’s procedures should include an anti-icing code, which indicates the treatment the aircraft has received. This code provides the flight crew with the minimum details necessary to estimate a HOT and confirms that the aircraft is free of contamination.

(3)After treatment. Before reconfiguring or moving the aircraft, the flight crew should receive a confirmation from the personnel involved in the operation that all de-icing and/or anti-icing operations are complete and that all personnel and equipment are clear of the aircraft.

(e)Holdover protection & LWE systems The operator should publish in the operations manual, when required, the HOTs in the form of a table or a diagram, to account for the various types of ground icing conditions and the different types and concentrations of fluids used. However, the times of protection shown in these tables are to be used as guidelines only and are normally used in conjunction with the pre-take-off check. An operator may choose to operate using LWE systems instead of HOT tables whenever the required means for using these systems are in place.

(f)Training The operator’s initial and recurrent de-icing training programmes (including communication training) for flight crew and for other personnel involved in de-icing operations should include additional training if any of the following is introduced:

(1)a new method, procedure and/or technique;

(2)a new type of fluid and/or equipment; or

(3)a new type of aircraft.

(g)Contracting When the operator contracts de-icing/anti-icing functions, the operator should ensure that the contractor complies with the operator’s training/qualification procedures, together with any specific procedures in respect of:

(1)roles and responsibilities;

(2)de-icing and/or anti-icing methods and procedures;

(3)fluids to be used, including precautions for storage, preparation for use and chemical incompatibilities;

(4)specific aircraft provisions (e.g. no-spray areas, propeller/engine de-icing, APU operation etc.);

(5)different checks to be conducted; and

(6)procedures for communications with flight crew and any other third party involved.

(h)Special maintenance considerations

(1)General The operator should take proper account of the possible side effects of fluid use. Such effects may include, but are not necessarily limited to, dried and/or re-hydrated residues, corrosion and the removal of lubricants.

(2)Special considerations regarding residues of dried fluids The operator should establish procedures to prevent or detect and remove residues of dried fluid. If necessary, the operator should establish appropriate inspection intervals based on the recommendations of the airframe manufacturers and/or the operator’s own experience:

(i)Dried fluid residues Dried fluid residues could occur when surfaces have been treated and the aircraft has not subsequently been flown and has not been subject to precipitation. The fluid may then have dried on the surfaces.

(ii)Re-hydrated fluid residues Repetitive application of thickened de-icing/anti-icing fluids may lead to the subsequent formation/build-up of a dried residue in aerodynamically quiet areas, such as cavities and gaps. This residue may re-hydrate if exposed to high humidity conditions, precipitation, washing, etc., and increase to many times its original size/volume. This residue will freeze if exposed to conditions at or below 0 °C. This may cause moving parts, such as elevators, ailerons, and flap actuating mechanisms to stiffen or jam in-flight. Re-hydrated residues may also form on exterior surfaces, which can reduce lift, increase drag and stall speed. Re-hydrated residues may also collect inside control surface structures and cause clogging of drain holes or imbalances to flight controls. Residues may also collect in hidden areas, such as around flight control hinges, pulleys, grommets, on cables and in gaps.

(iii)Operators are strongly recommended to obtain information about the fluid dry-out and re-hydration characteristics from the fluid manufacturers and to select products with optimised characteristics.

(iv)Additional information should be obtained from fluid manufacturers for handling, storage, application and testing of their products.

DE-ICING/ANTI-ICING — BACKGROUND INFORMATION Further guidance material on this issue is given in the ICAO Manual of Aircraft Ground De-icing/Anti-icing Operations (Doc 9640).

(a)General

(1)Any deposit of frost, ice, snow or slush on the external surfaces of an aircraft may drastically affect its flying qualities because of reduced aerodynamic lift, increased drag, modified stability and control characteristics. Furthermore, freezing deposits may cause moving parts, such as elevators, ailerons, flap actuating mechanism, etc., to jam and create a potentially hazardous condition. Propeller/engine/APU/systems performance may deteriorate due to the presence of frozen contaminants on blades, intakes and components. Also, engine operation may be seriously affected by the ingestion of snow or ice, thereby causing engine stall or compressor damage. In addition, ice/frost may form on certain external surfaces (e.g. wing upper and lower surfaces, etc.) due to the effects of cold fuel/structures, even in ambient temperatures well above 0 °C.

(2)Procedures established by the operator for de-icing and/or anti-icing are intended to ensure that the aircraft is clear of contamination so that degradation of aerodynamic characteristics or mechanical interference will not occur and, following anti-icing, to maintain the airframe in that condition during the appropriate HOT.

(3)Under certain meteorological conditions, de-icing and/or anti-icing procedures may be ineffective in providing sufficient protection for continued operations. Examples of these conditions are freezing rain, ice pellets and hail snow exceeding certain intensities, high wind velocity, and fast-dropping OAT. No HOT guidelines exist for these conditions.

(4)Material for establishing operational procedures can be found, for example, in:

(i)ICAO Annex 3 ‘Meteorological Service for International Air Navigation’;

(ii)ICAO ‘Manual of Aircraft Ground De-icing/Anti-icing Operations’;

(iii)SAE AS6285 ‘Aircraft Ground Deicing/Anti-Icing Processes’;

(iv)SAE AS6286 ‘Aircraft Ground Deicing/Anti-Icing Training and Qualification Program’;

(v)SAE AS6332 ‘Aircraft Ground Deicing/Anti-icing Quality Management’;

(vi)SAE ARP6257 ‘Aircraft Ground De/Anti-Icing Communication Phraseology for Flight and Ground Crews’;

(vii)FAA Holdover Time Guidelines

(viii)FAA 8900.xxx series Notice ‘Revised FAA-Approved Deicing Program Updates,Winter 20xx-20yy’.

(b)Fluids

(1)Type I fluid: Due to its properties, Type I fluid forms a thin, liquid-wetting film on surfaces to which it is applied which, under certain weather conditions, gives a very limited HOT. For anti-icing purposes the fluid/water mixture should have a freezing point of at least 10 °C below OAT; increasing the concentration of fluid in the fluid/water mix does not provide any extension in HOT.

(2)Type II and Type IV fluids contain thickeners which enable the fluid to form a thicker liquid-wetting film on surfaces to which it is applied. Generally, this fluid provides a longer HOT than Type I fluids in similar conditions.

(3)Type III fluid is a thickened fluid especially intended for use on aircraft with low rotation speeds.

(4)Fluids used for de-icing and/or anti-icing should be acceptable to the operator and the aircraft manufacturer. These fluids normally conform to specifications such as SAE AMS1424 (Type I) or SAE AMS1428 (Types II, III and IV). Use of non-conforming fluids is not recommended due to their characteristics being unknown. The anti-icing and aerodynamic properties of thickened fluids may be seriously degraded by, for example, inappropriate storage, treatment, application, application equipment, age and in case they are applied on top of non-chemically compatible de-icing fluids.

(c)Hold-over protection

(1)Hold-over protection is achieved by a layer of anti-icing fluid remaining on and protecting aircraft surfaces for a period of time. With a one-step de-icing/anti-icing procedure, the HOT begins at the commencement of de-icing/anti-icing. With a two-step procedure, the HOT begins at the commencement of the second (anti-icing) step. The hold-over protection runs out:

(i)at the commencement of the take-off roll (due to aerodynamic shedding of fluid); or

(ii)when frozen deposits start to form or accumulate on treated aircraft surfaces, thereby indicating the loss of effectiveness of the fluid.

(2)The duration of hold-over protection may vary depending on the influence of factors other than those specified in the HOT tables. Guidance should be provided by the operator to take account of such factors, which may include:

(i)atmospheric conditions, e.g. exact type and rate of precipitation, wind direction and velocity, relative humidity and solar radiation; and

(ii)the aircraft and its surroundings, such as aircraft component inclination angle, contour and surface roughness, surface temperature, operation in close proximity to other aircraft (jet or propeller blast) and ground equipment and structures.

(3)HOTs are not meant to imply that flight is safe in the prevailing conditions if the specified HOT has not been exceeded. Certain meteorological conditions, such as freezing drizzle or freezing rain, may be beyond the certification envelope of the aircraft.