Aircraft Deicing Aircraft De-Icing

Aircraft Deicing Update

ORDER: 8400.10

APPENDIX: 4

BULLETIN TYPE: Flight Standards Information Bulletin for Air Transportation (FSAT)

BULLETIN NUMBER: FSAT 04-05

BULLETIN TITLE: FAA-Approved Deicing Program Updates,

Winter 2004-2005

EFFECTIVE DATE: 10/26/04

M/M	ATA Code	14 CFR	PTRS
N/A	N/A	91, 121, 135	1381

TRACKING NUMBER:

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NOTE: THIS BULLETIN REQUIRES PTRS INPUT. SEE ITEM 9.

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1. PURPOSE. In 2003, the Federal Aviation Administration (FAA) revised the holdover time (HOT) guidelines to reflect new test results for heated Type I fluids and expanded the visibility tables associated with Type I HOT guidelines to accommodate very light snow conditions. These tables are not changed for winter 2004-2005. No new Type II fluids have been added or removed; therefore, all Type II HOT guidelines remain unchanged from those of the 2003-2004 icing season. A new Type III fluid has been introduced and its associated HOT guideline has been added for 2004-2005. A new Type IV fluid has been added, and a Type IV fluid no longer in production has been removed. These changes did not affect the Type IV generic HOT guidelines from winter 2003-2004. This bulletin provides the following:

A. Types I, II, III, and IV fluid HOT guidelines for fluids that meet the Society of Automotive Engineers (SAE) Aircraft Deicing/Anti-icing Fluid Specifications and associated guidelines for the application of these deicing/anti-icing fluid mixtures.

B. A listing of qualified Types I, II, III, and IV deicing/anti-icing fluids for the 2004-2005 icing season, including updated information.

C. Recommendations on various other ground deicing/anti-icing findings of the past year.

NOTE: The SAE no longer publishes HOT guidelines. The FAA, in coordination with Transport Canada (TC) and the SAE G-12 Aircraft Ground Deicing Holdover Time Subcommittee generated the HOT guidelines published herein. Test results from several independent testing laboratories and data analysis procedures endorsed by the SAE G-12 Aircraft Ground Deicing HOT Subcommittee were used to generate the HOT guidelines.

2. CANCELLATIONS. This bulletin cancels FSATs 99-07, 00-11C, 01-09A, 02-05, and 03-01; FAA-Approved Deicing Program Updates for Winter 1999-2000, Winter 2000-2001, Winter 2001-2002, Winter 2002-2003, and Winter 2003-2004, respectively.

3. BACKGROUND. Title 14 of the Code of Federal Regulations (14 CFR) part 121, section 121.629(c) requires that 14 CFR part 121 certificate holders have an approved ground deicing/anti-icing program, unless the certificate holder complies with part 121, section 121.629(d). Advisory Circular (AC) 120-60, Ground Deicing and Anti-Icing Program, provides guidance for obtaining approval of a ground deicing/anti-icing program and discusses the use of HOTs. Part 125, section 125.221, and part 135, section 135.227(b)(3), allow both kinds of certificate holders to comply with a part 121-approved program.

4. DISCUSSION.

A. HOT Guidelines.

(1) Contents.

(a) Appendix 1 includes revised FAA-approved HOT guidelines for SAE Type I, II, III, and IV fluids, as well as FAA-approved SAE guidelines for the application of these fluids. New for the 2004- 2005 icing season is a Type III HOT guideline for a Type III fluid which exhibits times typically less than those of Type II fluids but significantly longer than those of Type I fluids. Also, because of the difference in performance of specific Types II and IV deicing/anti-icing fluids available for this icing season, the FAA also included 14 (five Type II and nine Type IV) manufacturer-specific HOT guidelines. The manufacturer-specific Types II and IV HOT guidelines are as follows:

MANUFACTURER SPECIFIC TYPE II FLUIDS	MANUFACTURER SPECIFIC TYPE IV FLUIDS
KILFROST ABC-2000	UNION CARBIDE® (UCAR) ULTRA+
KILFROST ABC-II PLUS	OCTAGON® MAX-FLIGHT
OCTAGON E-MAX II	OCTAGON® MAX-FLIGHT 04
SPCA ECOWING 26 Type II	KILFROST® ABC-S
CLARIANT SAFEWING MPII 2025 ECO	CLARIANT SAFEWING MP IV 1957
	CLARIANT SAFEWING MP IV 2001
	CLARIANT MP IV 2012 PROTECT
	CLARIANT SAFEWING MP IV 2030 ECO
	SPCA AD-480 Type IV

(b) The FAA Type II (Table 2) and Type IV (Table 4) HOT guidelines comprise the generic HOT values and encompass the minimum (worst-case) HOT values for all fluids for a specific precipitation condition, temperature range, and fluid mixture concentration. Air carriers may only use the manufacturer-specific HOT guidelines (Tables 2A-2E and Tables 4A-4I) when these specific fluids are used during the anti-icing process. If a carrier cannot positively determine which specific Type II or IV fluid was used, it must use the HOTs from the generic Table 2 or 4, as appropriate.

(c) Also included (Table 6) is a list, by manufacturer brand name, of qualified Types I, II, III, and IV deicing/anti-icing fluids.

(d) Table 1B, which relates various snowfall intensities to prevailing visibilities, was expanded in 2003 to encompass very light snow conditions. To facilitate the use of Table 1B with Table 1 (the Type I HOT guidelines), color-coding was added. The color-coding is as follows:

Very Light Snow	Light Green
Light Snow	Light Yellow
Moderate Snow	Dark Yellow
Heavy Snow	Red

Table 1B may be used in estimating snow intensities for use with Type II, III, and IV HOT guidelines.

(e) Exercise caution during heavy snow (red) conditions, since no HOT guidelines exist. Although the meteorological approach to estimating snowfall rate has been based upon visibility, the HOTs of any anti-icing fluid are directly related to the amount of moisture (liquid equivalent snowfall) it can absorb prior to freezing. The revised snow intensities of Table 1B are based on investigations by the National Center for Atmospheric Research (NCAR) and APS Aviation of Montreal, Canada. During the 1995-2002 icing seasons, more than 7,000 observations of prevailing visibilities in snow, with liquid equivalent snowfall rates, for various temperature and day/night conditions, were recorded. These observations reveal that a combined visibility/temperature pair is required for a more accurate determination of snowfall intensities, and form the basis for the revised Table 1B. This table is essential for proper estimation of snowfall intensities, which are essential for determining liquid equivalent snowfall rates.

NOTE: The SNOW INTENSITY values of Table 1B are to be used mainly in conjunction with Table 1 for determining FAA Type I Fluid HOT guidelines for SNOW. However, Table 1B may also be used to estimate HOTs for snow columns of FAA Type II, III, and IV fluids.

(2) Type I HOT Guidelines.

(a) The Type I HOT guidelines (Table 1) remain unchanged for the upcoming 2004-2005 icing season.

(b)The Type I HOT values of the guidelines primarily are based on SAE-revised test methodologies to accommodate the effects of applying HEATED Type I fluids in determining their time of effectiveness for the various freezing precipitation conditions. Prior to the 2002-2003 icing season, Type I HOT values had been determined based on the application of unheated fluids. Recent findings indicate that the time of protection provided by Type I fluid (unlike Types II, III, and IV) is directly related to the heat input to aircraft surfaces. Type I fluid dilutes rapidly under precipitation conditions. Therefore, the heat that the aircraft surface absorbs will tend to keep the temperature of the fluid above its freezing point. Within practical limits, the more heat that an aircraft surface absorbs, the longer the surface temperature will remain above the freezing point of the fluid. Thus, the thermal characteristics of the aircraft’s surface affect HOTs. Theoretically, when the temperature of the surface equals the freezing point of the fluid, the fluid is considered to have failed. Because structural mass varies throughout an aircraft with a corresponding variation in absorbed heat, the fluid will tend to fail first in:

· Structurally thin areas

· Areas with minimal substructure, such as trailing edges, leading edges, and wing tips

NOTE: FAA Type I HOT guidelines are not approved for the application of unheated Type I fluid mixtures.

(c) The Type I HOT guidelines include three separate SNOW columns, representing the following categories: very light snow, light snow, and moderate snow conditions. Recent surveys and analysis of worldwide snow conditions have revealed that more than 75 percent of snow occurrences fall into the light and very light snow category. Values in the very light, light, and moderate snow columns are based on extensive tests conducted by APS Aviation of Montreal, Canada; the National Center for Atmospheric Research (NCAR) of Boulder, CO; and the Anti-Icing Materials Laboratory of Chicoutimi, Quebec, Canada, during several prior icing seasons. These tests were conducted on behalf of the FAA and TC. Previously, SNOW HOT guideline values were based on the then-current moderate snow conditions and a liquid equivalent snowfall rate of 1.0 to 2.54 mm/hr (0.04 to 0.10 in/hr of liquid equivalent snowfall). The SAE

G-12 committee has defined light snow as a snowfall rate of less than 1.0 mm/hr (less than 0.04 in/hr of liquid equivalent snowfall). During the meeting of the SAE G-12 HOT subcommittee in May 2003, values between 0.2 and 0.4 mm/hr were recommended for very light snow conditions. Thus, in the current FAA Type I HOT guideline, HOT values for liquid equivalent snowfall rates between 0.4 and 1.0 mm/hr (0.016 to 0.04 in/hr) are selected for the light snow column and HOT values for liquid equivalent snowfall rates between 0.2 and 0.4 mm/hr are selected for the very light snow column. Overall, these selections were based upon a number of factors, including:

· Snow intensity reporting and measurement inaccuracies for light conditions of less than 0.5mm/hr

· Potential wind effects

· Light snow variability

· Possible safety concerns associated with pretakeoff checks

(d) During the 2001-2002 winter icing period, more than 250 tests using heated Type I fluids in natural snow were conducted. These tests used an insulated thermal equivalent insulated 7.5 cm test box to simulate the thermal response of the leading edge of an aircraft wing instead of the standard “Frosticator Plate” used in prior years. Extensive laboratory and field tests had determined that the insulated 7.5 cm test box more closely matched the thermal response of an aircraft wing leading edge than the standard “Frosticator Plate.” During the tests, fluids were diluted to a 10 °C buffer and applied at 60 °C (140 °F) to the 7.5 cm insulated thermal equivalent test box. HOT results from these tests were deemed to more closely coincide with those observed during actual deicing operations in snow conditions.

(e) Note that in Table 1 there is a double diamond in the snow columns (Very Light Snow^uu, Light Snow^uu, and Moderate Snow^uu) with an accompanying note. The note states, “TO USE THESE TIMES, THE FLUID MUST BE HEATED TO A MINIMUM TEMPERATURE OF 60 °C (140 °F) AT THE NOZZLE AND AT LEAST 1 LITER/M² (» 2 GALS/100FT²) MUST BE APPLIED TO DEICED SURFACES.” When establishing compliance with the temperature requirement of 60 °C (140 °F) at the nozzle, the FAA does not intend for air carriers or deicing operators to continually measure the fluid temperature at the nozzle. The FAA deems that establishing the temperature drop (at nominal flow rates) between the last temperature monitored point in the plumbing chain and the nozzle is sufficient. Manufacturers of ground vehicular deicing equipment have indicated a temperature drop of 10 °C or less. Some manufacturers producing equipment that uses instant-on heat or last bypass heaters have indicated a temperature drop of 5 °C or less. Ensuring that the drop in fluid temperature from the last measured point in the plumbing chain to the nozzle does not preclude a fluid temperature of 60 °C (140 °F) at the nozzle is sufficient.

(f) Frozen contamination removal is the deicing step of a deicing/anti-icing procedure. It is emphasized that the use of HOT guidelines implies that an anti-icing step has been performed. The Type I HOT guideline also provides an estimate of the time of protection under precipitation conditions. The double diamond note on the Type I HOT guidelines implies the quantity of fluid that must be applied over and above that required to deice (i.e., the anti-icing step). As indicated in Table 1A for the one-step procedure, a single fluid is used to perform the deicing and anti-icing steps.

NOTE: HOTs start as soon as the anti-icing step begins. Users who rely on the one-step procedure (Table 1A) cannot assume that terminating the operation, after the frozen contamination has been removed, necessarily conforms to the intent of this table.

(g) The note further states that heated Type I fluid must be applied to a DEICED surface, implying that this is the anti-icing step. The minimum quantity stated in this note, “AT LEAST 1 LITER/M² (» 2 GALS/100FT²),” serves as a guide. This minimum quantity will vary depending on the aircraft, fluid application equipment, crew technique and experience, outside air temperature (OAT), and fluid spray pattern. Larger aircraft with greater skin thickness and more massive internal structure may require quantities greater than 1 LITER/M². The FAA does not intend for air carriers to measure this fluid quantity during the anti-icing step. For anti-icing, a moderate amount of Type I applied to drive-off all fluids that have absorbed snow, ice, and slush during the deicing process has proven safe. Experience with a particular aircraft can serve as the primary guide as to which surfaces are prone to fail first (e.g., wing tips, control surfaces, structurally thin areas, etc.). Such areas should receive adequate coverage of Type I fluid.

B. Interpretation of HOT Guidelines.

(1) The FAA intends for HOT guidelines to provide an indication of the APPROXIMATE length of time that a freezing point depressant (FPD) fluid will protect aircraft surfaces during icing conditions and while on the ground. The guidelines do not imply icing protection while airborne. Tables 2 and 4 have been termed generic or worst-case tables. Of all fluids tested for each Type II and Type IV fluid, the FAA has entered the lowest HOT value in each cell for each precipitation condition. Therefore, for any brand of fluid, its HOT will be as good as or better than the value in the appropriate worst-case chart. This can be important if the brand of fluid is not known. Some manufacturers of Types II and IV fluids have concurred in the publication of HOT guidelines for their particular fluid(s). These are termed “manufacturer specific” HOT guidelines. They are listed in:

· Tables 2A through 2E (for Type II fluids)

· Tables 4A through 4I (for Type IV fluids)

New for the 2004-2005 icing season is a Type III HOT guideline, which is derived from a recently certified Type III fluid.

(2) The HOTs of Type II, III, and Type IV FPD fluids are primarily a function of the OAT, precipitation type and intensity, and percent FPD fluid concentration applied. The icing precipitation condition (i.e., frost, freezing fog, snow, freezing drizzle, light freezing rain, and rain on a cold-soaked wing) implies that these meteorological conditions are active.

NOTE: All HOT values (except for snow) are determined in the lab under no-wind conditions. Generally, wind reduces HOT. Snow testing is conducted outdoors and may or may not involve varying winds. This can have varying effects on the test results.

(3) For Type II and Type IV fluids, the percent mix is the amount of neat fluid (as marketed by the manufacturer) in water. A 75/25 mix is, therefore, 75 percent FPD fluid and 25 percent water.

(4) For Type I fluid, (Table 1) note the statement in the commentary under that reads, “... FP of the mixture is at least 10°C (18°F) below OAT.” The difference between the FP (freezing point) of the fluid and the OAT is known as the temperature buffer. In this case, the buffer is 10°C (18°F), which you can interpret as the FP of the fluid being 10°C (18°F) below the OAT. The 10°C (18°F) temperature buffer is used to accommodate inaccuracies and impreciseness in determining the many variables that affect the FP of a fluid mixture. Some of these variables include:

· OAT measurements

· Refractometer FP measurements

· Temperature of applied fluid/water mixture

· Inaccuracies in FPD fluid/water mixtures volumes

· Differences between OAT and aircraft surface temperatures

· Changes in OAT following fluid application

· Differences in aircraft surface materials

· Degradation of FPD fluid strength due to aging

· Degradation of FPD strength due to pumping equipment

· Wind effects

· Solar radiation

EXAMPLE: If the OAT is -3 °C (27 °F), the FP of the Type I fluid mix should be -13 °C (9 °F) or lower and applied at a minimum temperature of 60°C (140 °F) at the nozzle before the HOT guidelines information in Table 1 can be used.

(a) In Table I under the ^oC column, below –3 °C to –6 °C for FREEZING DRIZZLE, the HOT is 0:05-0:09 minutes, which is interpreted as a HOT from 0 hours and 5 minutes to 0 hours and 9 minutes. Depending on the freezing drizzle intensity, the APPROXIMATE time of protection expected could be:

· As short as 5 minutes for a nominal drizzle intensity

· As long as 9 minutes for light drizzle conditions

(b) In all cells of Table 1, except for light and very light snow, where two values of time are entered, the precipitation intensity is light to moderate. For the very light snow and light snow columns, HOTs should be considered in terms of their respective rates. Very light snow has a liquid equivalent snowfall rate of 0.2 mm to 0.4 mm/hr and for light snow is 0.4 mm to 1.0 mm/hr. The longer times for very light snow would correspond to the lesser rate, whereas the shorter times would correspond to higher rates. Heavy precipitation conditions are not considered in any HOT guidelines.

NOTE: The FAA does not approve takeoff in conditions of moderate or heavy freezing rain.

(c) The FAA also emphasizes that air carriers should read and understand all notes and cautions (such as the reference to the 10 °C (18 °F) buffer) in the guidelines to preclude improper usage of the fluid. The caution notes are important to manufacturers’ specific tables because unique characteristics of a particular brand of fluid may warrant cautions not found in the generic or worst-case guidelines.

(5) Differences exist between Types II, III, and IV, and Type I fluid HOT guideline usage.

(a) A percent fluid concentration column appears in all tables dealing with Type II and IV fluids, but not in Table 1 (Type I fluids) and Table 3 (Type III fluid) because:

· Type I fluids are applied to maintain at least a 10 °C buffer between the OAT and the FP of the fluid/water mix

· Type III fluids are designed to be applied as a ready-mix (undiluted) and may be applied heated or unheated. Heated Type III fluid may be used in the removal and clean-up of residual Type II and Type IV fluids.

· Type II and IV fluids use concentrations of 100/0, 75/25, or 50/50 in the anti-icing application

NOTE: HOT tests are conducted using the 10 °C (18 °F) buffer for Type I fluids, undiluted ready-mix for the Type III, and the appropriate fluid/water concentration for Type II and Type IV fluids.

(b) The HOT for a Type I is considerably less than that of either a Type II, III, or IV. The amount of heat absorbed by aircraft surfaces during the deicing/anti-icing operations heavily influences the degree of protection provided by Type I fluid. To use the Type I HOT guidelines, the fluid must be applied heated to deiced surfaces with a minimum temperature of 60°C (140 °F) at the nozzle and applied at a rate of at least 1 LITER/M² (» 2 GALS/100 FT²).

(c) Although Type I fluids are normally considered deicing fluids and Types II, III, and IV are considered anti-icing fluids, all types have been used in the deicing and anti-icing mode. However, the performance of Type I fluid as an anti-icer is inferior to that of Types II, III and IV. Also, heated diluted Type II and IV fluids are being used for deicing and anti-icing operations. This is a common practice among many of the European airlines.

NOTE: The use of HOT guidelines are associated with anti-icing procedures and do not apply to deicing.

(d) During the application of heated Type II and IV fluids in the one-step procedure, questions have arisen regarding the anticipated HOT performance of these fluids. In prior advisory information, the FAA indicated that maximum anti-icing effectiveness could be achieved from the application of unheated (cold) Type II fluids to deiced aircraft surfaces. This was based upon observations of the performance of Type II fluids in production at that time. The rationale was that a cold, unheated fluid would produce a thicker protective layer on aircraft surfaces, thus providing longer protection than a heated fluid presumably applied in a thinner layer. Some air carriers proposed using the Type I HOT guideline values instead of Type II and IV values when these thickened, heated fluids were applied. Another carrier suggested reducing the Type II and IV HOT values by a factor of 50 percent. During tests conducted by APS Aviation for the FAA using existing test protocol, HOT performance of heated (60 °C) Type II and IV fluids was found to equal or exceed the HOT performance of unheated Type II and IV fluids for the same fluid concentrations, temperature, and precipitation conditions. Therefore, these and other test results indicate that there is no basis for reducing the current HOT guideline values for Types II and IV fluids or using the Type I fluid HOT guidelines when heated Type II and IV fluids are properly applied. In addition, HOT guideline data was obtained for the newly introduced Type III fluids when applied heated and unheated and no significant HOT performance differences were observed. Therefore, anti-icing applications of Type III fluids may be heated or unheated.

(e) Most FPD fluids are ethylene or propylene glycol-based. However, under precipitation conditions, chemical additives improve the performance of Type II, III, and IV fluids when used for anti-icing. These additives thicken and provide the fluid with non-Newtonian flow characteristics. Thickening enhances fluid HOT performance and the non-Newtonian aspect results in fluid viscosity rapidly decreasing during the takeoff roll, which allows the fluid to flow off the critical wing surfaces prior to lift-off.

(6) Tables dealing with Type II and Type IV fluids have a caution note (**) that states, “No holdover time guidelines exist for this condition below -10 °C (14 °F).” This statement informs the user that, although the temperature range is below “27 °F to 7 °F,” the FAA does not consider HOT values valid below -10 °C (14 °F) for freezing drizzle and light freezing rain. These conditions usually do not occur at temperatures below –10 °C. On rare occasions when these conditions do occur at temperatures below –10 °C, you should use caution regarding HOT value usage.

(7) Only one HOT value is entered under the FROST column for a given temperature band. Frost intensities or accumulations are low in comparison to other precipitation conditions and decrease at the colder temperatures. This usually results in HOTs for frost being considerably longer in comparison to HOTs for other precipitation conditions. The longer HOTs should accommodate most aircraft ground operational requirements. Furthermore, when testing in the laboratory for frost, only one precipitation condition is considered rather than a range. Thus, there is no HOT range for frost. You should only use the single time, as with all the times in the tables, as a guide. HOTs are for active frost conditions in which frost is forming. This phenomenon occurs when aircraft surfaces are at or below 0 °C AND at or below dew point. Frost typically forms on cold nights with clear skies.

NOTE: HOTs for frost are for ACTIVE frost conditions.

(8) A note appears at the bottom of the Type II, III and IV HOT guideline tables pertaining to the OAT and FP of the fluid and their relationship to the fluid’s aerodynamic performance. The user should obtain the Lowest Operational Use Temperature (LOUT) of the fluid from the manufacturer, which could be based on its aerodynamic performance (i.e., the fluid’s ability to flow off the wing during takeoff in extreme cold conditions).

C. HOT Guidelines Overview.

(1) The FAA has constructed generic HOT guidelines for Type I, II, III, and IV fluids (Tables 1, 2, 3, and 4, respectively) to present information on the minimum performance times that have been observed during testing of these deicing/anti-icing fluids.

(2) Typically, each cell of the HOT values represents a range of performance times in which the fluid provides acceptable protection for varying precipitation intensities for the following conditions:

· Freezing fog

· Snow

· Freezing drizzle

· Light freezing rain

· Rain on cold-soaked wings

NOTE: Except for the light snow, very light snow and light freezing rain conditions, the lower HOT value in a cell presents information for moderate precipitation conditions. The longer HOT value is representative of fluid performance for light precipitation conditions. HOT values for heavy precipitation conditions do not exist.

(3) In all Type II and IV HOT guidelines for the conditions of freezing fog, freezing drizzle, and light freezing rain, the HOT values in the temperature ranges of above 0 °C and –0 °C to –3 °C are the same for the 100/0, 75/25, and 50/50 fluid concentrations in a one-to-one comparison. This is due to the inability to recreate these precipitation conditions at temperatures above 0 °C in the laboratory. Testing is accomplished in the –0 °C to –3 °C range and the same values are entered in cells for above 0 °C.

(4) For Type I HOT guidelines, testing was conducted at

-3 °C and applied to the above -3 °C range. The FAA deemed potential differences between 0 and -3 °C HOT values for Type I fluid as insignificant because thermal energy is a key factor in achieving HOT performance for Type I fluid.

D. Unique HOT Guidelines.

(1) In the manufacturer’s specific Type IV HOT guidelines for Octagon MAX-FLIGHT (Table 4B), the data shows that protection is increased in some cells of the HOT when fluid concentration is reduced. Under the SNOW, FREEZING DRIZZLE, and LIGHT FREEZING RAIN columns, the 75/25 concentration provides a moderate increase in protection over the 100/0 concentration. The addition of certain quantities of water to some neat fluids can enhance their performance up to a certain point. For example, when water is added to Octagon MAX-FLIGHT it allows the fluid to build up thicker on a surface. In this instance, thicker does not mean a higher viscosity. During HOT testing, neat Octagon MAX-FLIGHT Type IV fluid typically exhibited a thickness of 0.7 mm on the test surface. When neat MAX-FLIGHT Type IV fluid was diluted with water to a 75/25 mix, the mix typically exhibited a thickness of 1.4 mm. Some of the tabular data for the MAX-FLIGHT Type IV fluid indicates this effect. Without knowing about this particular fluid mix phenomenon, an air carrier may think that the data presented in the tables is an error.

(2) Similar performance contradictions were observed (i.e., the 75/25 concentrations exceeded those of 100/0 concentrations) for the following fluids at FREEZING FOG conditions:

· Kilfrost ABC-II Plus (Type II)

· Kilfrost ABC-2000 (Type II)

· Clariant Safewing MP IV 1957 (Type IV)

(3) Another unique fluid is Ultra+® Type IV (Table 4A). There are no HOT values for this fluid in the 75/25 and 50/50 concentrations (i.e., no dilutions).

E. Snowfall Intensity -- Visibility Table. Table 1B presents critical information on the variability of snowfall intensities as a function of prevailing visibilities. The HOT of any anti-icing fluid is directly related to the amount of moisture it can absorb before freezing. Currently, snow intensities reported by the National Weather Service are the predominant means of providing flightcrews with information relating to the moisture content of precipitation. However, these snow intensities are typically based on the prevailing visibility.

(1) Snowflake density is a key factor in determining the moisture content of snow. Wet snow, which generally occurs at temperatures above –1 °C, has a greater density than dry snow. Also, being heavier, it will fall at a higher velocity than dry snow. Thus, for a given visibility, these two factors will cause wet snow to deposit more moisture than dry snow. Table 1B presents temperature correlation information, which more accurately relates wet snow and dry snow intensities to visibilities.

(2) During night snowfall conditions for the same snowfall rate, visibility is about twice as good as it is during the day. This occurs because snow reflects light at a high rate and, during the day, light comes from all directions, which makes the reflections worse. At night, there is less light and light rays are more directed toward you with reduced glare and reflections. Therefore, Table 1B also presents a differentiation between day and night conditions to make visibility a more accurate indicator of moisture content for a given snowfall intensity and temperature. Therefore, you must consult Table 1B for an accurate estimation of snowfall intensity moisture content (liquid equivalent snowfall rate), which is based on prevailing visibilities.

5. REVISIONS.

A. HOT Changes.

(1) The HOTs for Type I fluids remain unchanged from those of the 2003-2004 icing season version, which incorporate new color-coding and a very light snow column (see paragraph 4A(1)(d).

(2) The values in the Type II generic HOT guideline have not changed this upcoming icing season, since there were no new Type II fluids introduced nor were there any that had been removed due to non-production/non-availability for the required period of 4 years.

(3) A new Type III fluid, Clariant MP III 2031 ECO, is introduced for the upcoming 2004-2005 icing season with a corresponding generic HOT guideline (Table 3). Type III fluid is designed primarily for aircraft with low rotation/takeoff speeds, and offers substantial improvements in anti-icing performance when compared to Type I fluid. Also, it does not require specialized low shear application and transfer equipments. This particular fluid was designed to be used in Type I storage tanks and application equipment, either diluted or undiluted for deicing and undiluted (ready-mix) for anti-icing. In the future, Type III fluids that can be diluted for anti-icing may be developed. Type III fluids can be applied heated or unheated for anti-icing.

(4) The HOT values of the Type IV generic HOT guideline have not changed the 2004-2005 icing season, although one Type IV fluid, Clariant Safewing IV, was removed since it has not been in production or available for the required period of time. Also, a new Type IV fluid, MAX Flight 04, has been introduced. HOT data from both of these fluids exceeded HOT guideline values in the generic table; therefore, their respective removal and addition did not affect the generic Type IV HOT guideline table. A manufacturer’s specific HOT guideline for MAX Flight 04 (Table 4C) has been added.

(5) The viscosity and measurement criteria are noted at the top of each manufacturer’s specific Type II and IV HOT tables. These viscosity values are the lowest on wing viscosities (LOWV) at which the fluid can reasonably be expected to provide HOTs consistent with those in the manufacturer’s specific (brand name) HOT guidelines. They are for the user’s information and not anticipated to be used by, or made available to, flightcrews. However, the user should periodically verify this published viscosity to ensure that the HOTs expected correspond with those in the appropriate table.

NOTE: Differences in pumping equipment can result in varying degrees of fluid shearing/degradation with corresponding variations in viscosity measurement. This may result in slight deviations from published HOT values. However, in all cases, the fluids noted in this bulletin have been fully qualified. The HOT values associated with each fluid are, as with all HOT values, guidelines only.

B. Table 1A -- Type I Fluid Application Table. In 2003, the FAA, in coordination with the SAE G-12 Methods Subcommittee, modified the temperature application requirements for both the one-step and the two-step procedure deicing/anti-icing procedures to reflect the requirement for applying HEATED Type I fluid. The revised note states:

“Mix of fluid and water heated to 60°C (140°F) minimum at the nozzle with a freezing point of at least 10°C (18°F) below OAT.”

Also, the following note was added: “NOTE: This table is applicable for the use of Type I Holdover Time Guidelines. If holdover times are not required, a temperature of 60°C (140°F) at the nozzle is desirable.” In essence, this note clarified the requirements for heated Type I fluids mixtures if Type I holdover times are required.

C. Several changes have been incorporated into Table 5, “FAA Guidelines for the Application of SAE Type II, Type III, and Type IV Fluid Mixtures.” All of these changes, which appear under both the One-step Procedure and the Two-step Procedure columns, are related to the addition of a Type III fluid for the upcoming 2004-2005 icing season. Of particular note is that the Type III fluid must be applied as an undiluted ready-mix if HOT guidelines are to be applied.

D. Several Type I fluids have been removed and several new Type I fluids have been added to Table 6, “List of Qualified Deicing/Anti-icing Fluids – Winter 2004-2005.” There was no change to the Type II fluids list. A Type III fluid has been added and one Type IV fluid has been removed and a new Type IV fluid has been added. The note at the bottom of the table has been change to read, “The qualified fluids on this list have met applicable SAE AMS specifications requirements for aerodynamic performance, water spray endurance test (WSET), and high humidity endurance tests (HHET), as conducted by the Anti-Icing Materials Laboratory at the University of Quebec at Chicoutimi, in effect at the time of certification.” Other qualification tests -- such as physical properties, toxicity, material compatibility, thermal stability, etc. -- are conducted by other organizations and, if required, these test results should be obtained directly from the fluid manufacturer. Also, Material Safety Data Sheets (MSDS) should be obtained from the fluid manufacturer.

E. Fluid Quality Control Checks. Prolonged or repeated heating of fluids may result in loss of water, which can lead to performance degradation of the fluid. For Type I fluids, the water loss may cause undesirable aerodynamic effects at low temperatures and for Type II, III, and IV fluids, the thermal exposure and/or water loss may cause a reduction in fluid viscosity leading to lower HOTs. Other fluid degradations may result from chemical contamination or excessive mechanical shearing attributable to the use of improper equipments/systems such as pumps, control valves, or application devices. It is recommended that checks be made of fluid quality prior to the start of the deicing season, prior to daily usage, and following system maintenance or after a fluid concentration change. As a minimum, checks should include visual inspections and refractive index measurements and pH measurements if fluid contamination is suspected. All of these measurement values should be within the limits recommended by fluid manufacturers. In addition, for Type II, III, and IV fluids, the FAA advises that viscosity checks be performed if fluid degradation is suspected. If viscosity checks are conducted, they should be performed in accordance with (IAW) fluid manufacturers’ recommendations.

6. OTHER CONCERNS/CONDITIONS.

A. Inspection of Single-Engine High Wing Turboprop Aircraft.

(1) In recent years, there has been a disproportionate number of ground icing accidents associated with improper checking/inspection of single-engine high wing turboprop aircraft employed in commercial service. This is especially true of those single-engine high wing turboprop aircraft operated from remote locations with minimum facilities. In several of these accidents it could not be determined whether the aircraft had been inspected/checked by the operator/pilot prior to departure attempt. Holdover times were not an issue, since at the time of attempted departure, there was no active precipitation, and typically these accidents usually occurred during the first flight of the day, following a freezing precipitation event that had occurred earlier.

(2) For these types of operations, the single pilot/operator was usually the final person to perform the pre-takeoff check. On one aircraft in particular, it has been shown that it is difficult to see clear frozen contaminations from a glancing view of the upper wing surface area (looking rearward from the wings leading edge) when the pilot uses the wing strut/step to see the aft portion of the wing. Visual inspections can best be achieved, by using inspection ladders or deicing ladders, to achieve a higher vantage point so as to view the aft upper wing surface area. A number of ladder manufacturers provide wing inspection ladders that are ideal for this task. Principal operations inspectors (POI) are encouraged to discuss these observations with their operators, and to ensure that operators employ adequate means to allow a pilot to clearly see the entire upper wing surface from a suitable height above the wing.

B. Residual Fluid Accumulations.

(1) Incidents of severe airframe vibration or limit cycle oscillations (LCO) in-flight have been reported for certain medium-sized turbojet aircraft following ground deicing/anti-icing of the horizontal stabilizer. These incidents have been attributed to an accumulation of deicing/anti-icing fluids and/or other residue in the elevator balance panel’s cavities and on external surfaces of the elevator tab. The fluid may have accumulated in the balance bays due to inadequate drainage provisions on certain series of these aircraft. Also, the current design of the elevator tab has been found to be aerodynamically sensitive to the accumulation of foreign materials on its surfaces. Drainage provisions on later series of these aircraft are improved over those that have experienced the airframe vibrations and LCOs. Additionally, the aircraft manufacturer has indicated that it has completed developmental designs for an improved elevator tab, which is less susceptible to the accumulation of foreign substances on its external surfaces.

(2) As an interim measure, the FAA issued, in 2002, an Airworthiness Directive (AD) covering the affected aircraft to mitigate possible future incidents of this nature (refer to FAA AD 2002-08-20, Airplane Flight Manual (AFM) – Limitations Section – Airspeeds). The AD required the following:

· Repetitive cleaning of the elevator tab following every ground deicing of the horizontal stabilizer

· A one-time cleaning of the elevator balance bays

· Modifications of the airplane flight manual (AFM) to limit airspeeds under certain conditions and provide the flightcrew with information relative to LCO

As of this bulletin’s publication, a redesign of the elevator trim tab of aircraft affected by this AD has been completed by the aircraft manufacturer and requirements of AD-2002-08-20 have been superceded by AD 2003-03-22. This new AD requires the modification of the elevator and elevator trim tabs IAW the aircraft manufacturer’s Alert Service Bulletin. All affected aircraft are to be modified before 18,000 flight cycles or before March 12, 2005.

C. Fluid Dry-Out.

(1) Reported incidents of restricted movement of flight control surfaces, while in-flight, attributed to fluid dry-out have continued. Testing has shown that diluted Type II and IV fluids can produce more gel than neat fluids.

NOTE: Changing from Type IV to II will not necessarily result in an improvement.

(2) Such events may occur with repeated use of Types II and IV fluids without prior application of hot water or Type I fluid mixtures. This can result in fluid collecting in aerodynamically quiet areas or crevices, which do not flow off the wing during the takeoff ground roll. These accumulations can dry to a gel-like or powdery substance. Such residues can rehydrate and expand under certain atmospheric conditions, such as high humidity or rain. Subsequently, the residues freeze, typically during flight at higher altitudes. Rehydrated fluid gels have been found in and around gaps between stabilizers, elevators, tabs, and hinge areas. This especially can be a problem with non-powered controls. Some pilots reported that they have reduced altitude until the frozen residue melted, which restored flight control movement.

(3) Several European air carriers have reported this condition in which the first (deicing) step was a diluted heated Type II or IV fluid and followed by a Type II or IV fluid as the second (anti-icing) step. Yet, North American air carriers have not reported such occurrences. Typically, North American air carriers use a two-step deicing/anti-icing procedure in which the first step is generally a hot Type I fluid mixture.

(4) The FAA has suggested that high-pressure washing in accordance with the aircraft manufacturers’ recommendations, with a hot Type I fluid/water mix in areas where fluid could accumulate, may alleviate the problem. For those locations equipped with Type III fluids, in lieu of Type I fluids, it is suggested that a high pressure washing with a heated Type III/water mix be employed. Such a procedure may require subsequent lubrication. If unsuccessful, fluid dry-out may become a maintenance issue, making appropriate procedures necessary to address the problem. Increasing the frequency of inspection may be necessary if fluid dry-out with consequent restricted flight control movement becomes a recurring problem.

(5) You should check aircraft surfaces, quiet areas, and crevices for abnormal fluid thickening, appearance, or failure before flight dispatch, especially if Type II or IV fluids are used exclusively. If you suspect residue as a result of fluid dry-out, spray with water from a spray bottle and wait 10 minutes. Residue will rehydrate in a few minutes and be easier to identify. This residue may require removal before takeoff.

D. Freezing Fog. The freezing fog condition is best confirmed by observation. If there is accumulation in the deicing area, then the condition is active and freezing fog accumulation will tend to increase with increasing wind speed. The least accumulation (0.5 gm/dm²/hr) occurs with zero wind. The measured deposit rate of freezing fog at 1 and 2.5 meters/sec wind speeds are 2 and 5 gm/dm²/hr, respectively. Higher accumulations are possible with higher wind speeds. Although the wind can affect fluid performance through high deposition rates, this factor is not accommodated for when generating fluid HOTs.

7. NEW TECHNOLOGY.

A. Gas-Fired Infrared (IR) Systems.

(1) A gas-fired IR system contained in a modular shelter facility is in operation at several airports, including the Continental IR deicing facility at Newark International Airport. This system uses gas-fired units suspended from the ceiling of the modular shelter facility. It imparts sufficient IR focused energy on the aircraft surfaces, which melts the frozen contaminants on the aircraft’s surfaces that are in the line-of-sight of the IR units. This system has been used to deice commuter and moderate size (B-737) aircraft.

(2) With regard to such facilities, frozen contamination should be removed from aircraft surfaces before dispatch from the facility or anti-icing. The latter is generally accomplished within the facility, after the deicing step, with the IR radiant energy at a reduced intensity. The reduced intensity during the anti-icing step is intended to prevent re-accumulation of frozen contamination (e.g., snow) that may blow through the open ends of the facility.

NOTE: The dehydration of Types II and IV fluids, which may occur during constant and uninterrupted exposure to IR radiation, can adversely affect fluid performance. The FAA advises the user to contact the manufacturer of the IR deicing facility and/or fluid manufacturer to determine the limit of IR exposure to which the fluid can be safely subjected without a degradation of fluid performance.

(3) The IR units may continue to operate between the deicing and anti-icing steps to evaporate the frozen contamination that has melted. The FAA cautions that heated aircraft surfaces must not exceed manufacturer’s limits. After removal of the IR energy source, surfaces that remain wet will require an application of heated deicing fluid to preclude refreezing. When required (for operations other than frost or leading edge ice removal and when the OAT is at or below 0 °C (32 °F), an additional treatment with heated deicing fluid must be performed within the facility to prevent refreezing of water, which may remain in hidden areas.

B. Mobile IR Systems. A mobile IR deicing system that melts frozen contaminants from exposed aircraft surfaces continues to be developed. This system consists of a moveable, boom-mounted heating panel installed on a truck. Temperature controlled flameless catalytic heaters fueled by natural or propane gas generate the IR heat. During operations, these heater panels are normally situated several feet from the aircraft surfaces and use temperature sensors to measure aircraft surface temperatures. This system was used in the United States Air Force (USAF)-sponsored Aircraft Ground Deicing Evaluation exercise, conducted at the USAF Eglin Air Force Base (AFB) McKinley Cold Chamber in the spring of 2002. The FAA anticipates that these units will usually be employed in pairs (or more).

C. Forced Air Deicing Systems (FADS).

(1) Overview. The military and foreign air carriers have used FADS for years, but these were largely limited to the removal of loose snow. Many of these systems were converted APUs and had a tendency to be unwieldy.

(a) The current generation of FADS is easier to handle and designed to remove frozen contamination by the use of forced air and forced air augmented with a Type I fluid injected into its high-speed air stream. Although heated fluid is more effective, the fluid can be heated or unheated. Due to compression heating, expect air temperature to rise. Depending on the specific FADS, the operator may be able to select from several FAD modes, including:

· Forced air alone

· Forced air augmented by Type I fluid

· Type II and IV fluids applied over or injected into the forced air stream

NOTE: These capabilities make the current generation of FADS more versatile than its predecessors.

(b) Some systems have an additional mode of operation, a fluid-only mode. Generally, this mode is not as effective as the application of Type I using conventional equipment, mainly because a FADS system expels less fluid.

(c) Some systems have been retrofitted onto operational deicing vehicles while maintaining the vehicle’s original capability. This enables the vehicle to operate as a FADS or conventional deicer. A separate vehicle and deicing system operator are usually required. However, some units may be fully operated from the deicing bucket/cab. In a typical hybrid deicing system, the fluid and forced air are discharged coaxially with a separate nozzle/spray system being used for the anti-icing application of Type II and IV fluids. In a manner similar to typical deicing operations, directional control of the discharge nozzle is accomplished from controls in the deicing bucket/cab.

(2) Possible Concerns with FADS.

(a) The guidelines previously noted that Type I fluid was injected into the high-speed air stream. Generally, FADS units are not limited to Type I fluid. However, testing has indicated that degradation to the viscosity of Type II and IV fluids may occur when applied by a FADS. This degradation appears to be influenced by the velocity and pressure of the forced air stream and the distance between the forced air nozzle and surface being deiced. For direct injections, FPD fluid viscosity degradation has been shown to increase as the forced air velocity increased and as the distance between the FADS nozzle to the surface being deiced decreased.

(b) Additionally, FADS-applied fluid/mixtures may be unduly aerated. Both of these factors may result in lower-than-published HOTs for Type II and IV fluids.

(c) Another factor that may reduce HOT in the air/fluid mode for all fluids is the apparent tendency of the high-speed air stream to thin out the fluid film as it is being applied. Limited testing suggests such a possibility and indicates that less fluid is required to remove frozen contamination as compared to conventional deicing methods. However, for certain types of icing contamination, more time may be required to deice using a FADS.

(d) During the 2002-2003 icing season, the FAA and TC, in conjunction with two air carriers, conducted tests to characterize the deicing performance of FADS and their effects on HOT guidelines. Tests were conducted at several locations, using the FADS in both the fluid injection mode and in the air-assist mode.

(i) In the injection mode, Type IV anti-icing fluids were injected directly into the forced air stream of the forced air delivery system; in the air-assist mode, anti-icing fluids were applied over the forced air stream and allowed to drip/fall into the forced air stream. The desired results included validation of the ease of application of anti-icing fluids to include increased application distances and easier spreading of fluids on aircraft surfaces. Also tested was the potential for the use of less fluid during the anti-icing procedure.

(ii) Following application using both the injection mode and the air-assist mode, the applied fluids were recovered and subjected to analysis for viscosity, aeration, and HOT performance. Results of viscosity evaluations from the fluids recovered from the air-injection mode were determined to be unacceptable. Significant decreases in the fluids’ viscosities on the order of 40-50 percent were observed. Thus, the conclusion was that HOT Guidelines should not be used when the anti-icing fluids are directly injected into the forced air stream. Use of the air-assist mode to apply anti-icing fluid to deiced surfaces produced viscosities that were endorsed for the 2003-2004 icing season. The units/equipment/fluid involved included:

· FMC LMD deicing truck

· Forced air delivery pressure @ 13 psi

· Forced air pressure @ 100/lbs/min

· Type IV fluid nozzle rated @ 20-25 GPM @ 50 psi

· Fluid brand: Clariant Safewing MP IV 2001

(e) During the 2003-2004 icing season, additional tests were conducted in conjunction with an air carrier. These tests, employing six Type IV fluids, were designed primarily to assess the effects of applying Type IV fluids in the air-assist mode from a FADS. The fluids were applied employing both conventional anti-icing applications methods and the forced air-assist method. FMC LMD-2000 and the FMC Tempest II Ground Deicing Equipment with standard application pressures and flow-rates were employed in the tests. Two fluid viscosity measurement samples were taken from four sources/locations during the process. These included:

· Fluid Delivery Tote,

· Truck Tank,

· Test Wing employing conventional anti-icing application

· Test wing employing forced air-assist application

Prior to measuring viscosities, the fluid samples were centrifuged to remove entrapped air bubbles as recommended in Brookfield viscosity measurement practices.

(i) Results were mixed. The shear imparted into four of the six fluids tested produced viscosities below acceptable LOWVs, and these fluids were deemed to not be satisfactory for forced air-assist applications. The LOWV represents the lowest viscosity that a fluid should have after it has been applied to an aircraft wing. Applied fluids with viscosities lower than the LOWV may produce HOTs shorter than those given in the HOT guidelines. Two of the fluids produced samples that exhibited viscosities above the LOWVs. However, the acceptable viscosities were deemed to be a function of the initial viscosities of the samples tested. One fluid, Clariant Safewing MP IV 2001, was found to produce acceptable viscosity values above its LOWV when its initial viscosity was within 90% of the upper end of its production range of 30,000 cP. The other fluid, Clariant Safewing MP IV 2012 Protect, was found to produce acceptable viscosity values above its LOWV when its initial viscosity was within 75% of the upper end of its production range of 20,000 cP.

(ii) The salient characteristics of two Type IV fluids that were found to exhibit acceptable viscosities when applied by forced air-assist from the FMC LMD-2000 or FMC Tempest II ground equipment are as follows:

FLUID

LOWV (cP)

High End of Production Range (cP)

TOTE VISCOSITY (cP)

CLARIANT SAFEWING MP IV 2001

18,000

30,000

27,000

CLARIANT SAFEWING MP IV 2012 PROTECT

7,800

20,000

15,000

(iii) Thus, at this time, due to the uniqueness of the Type IV fluids tested, the FAA will only endorse the use of Type IV HOT guidelines for the above mentioned FAD equipment and the Clariant Safewing MP IV 2001 and the Clariant Safewing MP IV 2012 Protect Type IV fluids which exhibit Tote viscosity values of 27,000 and 15,000 cP, respectively, for air-assist applications.

(iv) Additional anti-icing fluids employing forced air delivery systems that have been optimized for anti-icing applications (i.e., lower air pressures, different fluid velocities and spray patterns, different contact angles between the forced air stream and the fluid spray) may prove to provide acceptable HOT results when applied in the air-assist mode. During the upcoming 2004-2005 icing season, additional tests are planned in which other fluids and forced air equipment configurations will be evaluated.

(f) Also, note that forced air or air/fluid applications may not eliminate the need for conventional fluid deicing and anti-icing for all types of freezing/frozen precipitation.

NOTE: Except for the equipment and fluid mentioned above in the air-assist mode, you should not use published HOT guidelines when using forced air, unless followed by the application of deicing and anti-icing fluid without forced air. The fluids should be applied in accordance with standard application procedures, such as presented in FAA advisory material and/or SAE document ARP4737.

(g) FADS vary in many respects (e.g., airflow pressure and rate, fluid flow pressure and rate, and optimum effective distance with and without fluid injection). Currently, these factors make it difficult to be specific with procedures without conducting actual tests. Adhere to the usual manufacturer cautions when operating FADS. For example, do not exceed the airframe manufacturer’s limits regarding surface temperature and pressure in the air or air/fluid impact areas. The FADS and airframe manufacturer literature should be consulted.

(3) Additional Precautions for FADS.

(a) Ear protection will normally be used and is required when noise levels exceed 85 decibels (dB).

(b) Exercise caution around ground personnel. The potential for blown ice chunks striking ground personnel and the restriction to visibility due to blown loose snow are possible problems.

· Directing forced air into sensitive aircraft areas

· Blowing snow or slush into landing gear and wheel well areas

· Blowing ice, snow, and slush into aircraft engine inlets, APU inlets, and control surface hinge areas

NOTE: You should obtain information regarding a specific system from its manufacturer’s technical literature. The SAE document ARD 50102, “Forced Air or Forced Air/Fluid Equipment for Removal of Frozen Contaminants,” provides information on forced air systems and their usage.

D. Non-Glycol-Based Deicing/Anti-Icing Fluids. In recent years, new non-glycol-based Type I deicing/anti-icing fluid have been qualified to the requirements of AMS-1424. These fluids, based upon glucose-lactate combinations and other formulations, successfully completed qualification tests and were considered to be environmentally benign when compared to glycol-based deicers. One of these fluids, Metss ADF-2, was a slightly different formulation of the earlier non-glycol-based Metss ADF fluid. The USAF undertook initial use of the Metss fluid in 2003; however, results were unfavorable. Consequently, the USAF withdrew this fluid from service, citing undesirable stickiness and tackiness of residual fluids. Therefore, the METSS ADF-2 Type I fluid is removed from the FAA-qualified fluids list for 2004-2005.

E. Ground Ice Detectors (GID). GID developments have continued during the past year. These include wide-area, hand-held ice detection systems that use advanced optical technology capable of quickly detecting aircraft contamination from distances up to 200 feet from the aircraft. GIDs have shown a potential for more efficient deicing operations; however, these devi