* High-lift devices such as leading-edge slats and leading or trailing-edge flaps;
* Propellers;
* Spoilers and speed brakes;
* All control surfaces and control balance bays;
* Engine inlets, particle separators, and screens;
* Windshields and other windows necessary for flight crew visibility;
* Antennas;
* Fuselage;
* Exposed instrumentation devices such as angle-of-attack vanes, pitot-static pressure probes, static ports, and temperature probes;
* Fuel tank and fuel cap vents;
* Cooling and auxiliary power unit (APU) air intakes, inlets, and exhausts; and * Landing gear.
PRETAKEOFF CONTAMINATION CHECKS FAR Parts 135 and 125 require that a pretakeoff contamination check be completed within 5 minutes prior to beginning takeoff.
A pretakeoff contamination check is a check to make sure the wings and control surfaces are free of frost, ice, or snow.
Procedures for conducting this aircraft type specific check must be approved by the certificate holder's principal operations inspector (POI) and referenced or described in the certificate holder's operations specifications.
CAUTION: Under extreme weather or operational conditions contamination can occur in less than 5 minutes.
The components that can be checked vary by aircraft type and design. In some aircraft, the entire wing and portions of the empennage are visible from the cockpit or the cabin. In other aircraft, these surfaces are positioned such that only portions of the upper surface or lower surface of the wings are in view.
Undersurfaces of wings and the undercarriage are viewable only from high-wing-type aircraft. A practice in use by some operators is to perform a visual inspection or check of wing surfaces, leading edges, engine inlets, and other components of the aircraft that are in view from either the cockpit or cabin, whichever provides the maximum visibility. The PIC may require the assistance of trained and qualified ground personnel to
conduct the pretakeoff contamination check.
If any aircraft surfaces have not been treated with FPD fluid, the PIC or another trained crewmember should look for, and examine any evidence of, melting snow and possible freezing. If the aircraft has been treated with FPD fluids, aircraft surfaces should appear glossy, smooth, and wet. If these checks indicate accumulations of ice, snow, or frost, or ice formation that may have been induced by taxi operations, the aircraft should be re-deiced/anti-iced.
TYPES OF DEICING AND ANTI-ICING
EQUIPMENT AND FACILITIES General - Manual methods of deicing provide a capability, in clear weather, to clean an aircraft adequately to allow a safe takeoff and flight. In inclement, cold weather conditions, however, the only alternative is sometimes limited to placing the aircraft in a protected area such as a hangar to perform the cleaning process by available means. A common practice developed is to clean the aircraft in the hangar and provide a protective coating of FPD fluid (anti-icing) to protect the aircraft from ice or snow accumulation for a limited period of time prior to takeoff. Most modern airports have traffic conditions and limitations of hangar space that, for the most part, preclude indoor ground deicing. These airports usually have one or more fixed base operators who have the equipment, capability, and experience to clean the aircraft and provide brief protection to allow a safe takeoff to be performed. Many airlines have repositioned ground deicing equipment for ramp deicing at major airports where icing conditions are prevalent in the United States, Canada, and European countries. Some airports or operators have installed permanently stationed equipment at central locations where aircraft can be deiced and anti-iced.
Discussions of these types of facilities are contained in AC 20-117 and AC 150/5300-14.
Warm Hangars - Early methods employed the use of hangars to avoid exposure to the elements or to provide a place for warming the aircraft and melting ice, frost, and snow formations prior to departure. This method generally requires that all moisture that could freeze is either removed or the aircraft is also treated with FPD fluid to preclude freezing upon removal of the aircraft from the warm hangar into below freezing ambient conditions.
Some operators use warm hangars for the complete deicing and anti-icing process with fluids.
Wing and Other Covers - The use of wing covers and covers for other critical components such as windshields, engine air intakes, pitot probes, etc., are useful to lessen the extent of manual work or deicing fluid required to remove frost, snow, or other ice formations from the aircraft.
Mechanical Methods - Various devices such as brooms, brushes, ropes, squeegees, fire hoses, or other devices; have been used to remove dry snow accumulations, to remove the bulk of large wet snow deposits, or to polish frost to a smooth surface. These
manual methods require that caution be exercised to preclude damage to aircraft skins and other critical components.
Deicing and Anti-icing Fluids - These fluids are used for quickly removing frost and to prevent or retard ice formation during overnight storage. In addition, they are used to assist in melting and removal of snow or other ice formations such as would develop as a result of freezing rain or drizzle, and for assisting in the removal of ice or frost formations accumulated during a previous flight.
DEICING/ANTI-ICING EQUIPMENT COMMONLY
USED FOR SMALL AIRPLANES Portable Spray Equipment and Dispensers - Various methods of applying FPD fluids have been utilized in the past, such as use of portable, pressurized containers with spray wands, mopping the fluid on the surface requiring treatment from a bucket, use of hand pumps attached to a supply tank and spreading the solution with a mop, brush or other suitable devices to, in time, melt the ice to the extent that it can be removed by manual means.
Mobile Deicing and Anti-icing Equipment - Several manufacturers of various types of aircraft ground deicing equipment exist today to meet the ground support equipment demands of the aviation community. These ground support equipments vary in types from simple trailers hauling a 55 gallon drum of FPD fluid with a wobble pump and mop to sophisticated equipment capable of heating and dispensing large quantities of water and deicing fluid and capable of elevating deicing personnel to heights necessary to have access to any area of the largest of today's aircraft. Some of this equipment may not be compatible for use on small airplanes because of the very high pressures and very high temperatures used in the deicing process for large airplanes.
Central and remote deicing Deicing and anti-icing near the departure end of the runway has obvious advantages, some of which are highlighted as follows:
* Provides a place for conducting pretakeoff contamination checks.
* Reduces the time between deicing/anti-icing and takeoff.
This practice is encouraged where adequate facilities exist and if performed by trained and qualified personnel.
DEICING AND ANTI-ICING FLUIDS Common practice, developed by the North American and European aviation communities over many years of experience, is to deice and anti-ice an aircraft before takeoff. Various techniques of ground deicing and anti-icing have been developed. The most common of these techniques is to use FPD fluids in the ground deicing process and to anti-ice with a protective film of FPD fluid to delay the reforming of ice, snow, or frost.
Commercially available FPD fluids used for aircraft deicing are ethylene glycol or propylene glycol based. The general characteristics of these fluids are described in table 1.
The basic philosophy of using FPD fluids for aircraft deicing is to decrease the freezing point of water in either the liquid or crystal (ice) phase. FPD fluids are highly soluble in water;
however, ice is slow to absorb FPD or to melt when in contact with it. If frost, ice, or snow is adhering to an aircraft surface, the formation may be melted by repeated application of proper quantities of FPD fluid. This process can be significantly accelerated by thermal energy from heated fluids.
As the ice melts, the FPD mixes with the water thereby diluting the FPD. As dilution occurs, the resulting mixture may begin to run off. If all the ice is not melted, additional applications of FPD become necessary until the fluid penetrates to the aircraft surface. When all ice has melted, the remaining liquid residue is a mixture of water and FPD. The resulting film could freeze (begin to crystallize) with only a slight temperature decrease.
---------------------------------------------------------------- Table 1. General Characteristics of Commercially Available FPD's _________________________________________________________________ Common ¦ Primary ¦Viscosity¦Primary ¦ Notes Name ¦ Active ¦ ¦ Use ¦ ¦Ingredients¦ ¦ ¦ ___________¦___________¦_________¦________¦______________________ Traditional¦Ethylene, ¦ ¦ ¦ Includes North ¦propylene, ¦ ¦ ¦*SAE AMS 1425, SAE American ¦diethylene ¦ Low ¦Deicing ¦AMS 1427, AF 3609, ¦glycols &/ ¦ ¦ ¦Mil-A-4823, other pre- ¦or isopropyl ¦ ¦1993 Mil-Spec Fluids & ¦ alcohol ¦ ¦ ¦other commercially ¦ ¦ ¦ ¦available fluids ___________¦___________¦_________¦________¦______________________ AEA Type I ¦Propylene, ¦ ¦ ¦Propylene Glycol based SAE Type I ¦ &/or ¦ Low ¦Deicing ¦fluids not to be (AMS 1424) ¦diethylene ¦ ¦ ¦used undiluted @ OAT ISO Type I ¦ glycol ¦ ¦ ¦< 14 degrees F (10 ¦ ¦ ¦ ¦degrees C). Aircraft ¦ ¦ ¦ ¦performance changes ¦ ¦ ¦ ¦may result.
___________¦___________¦_________¦________¦______________________ ¦Propylene ¦ ¦ ¦ AEA Type II¦ &/or ¦ ¦Deicing ¦ SAE Type II¦diethylene ¦ Low ¦ and ¦For use on aircraft (AMS 1428) ¦ glycol ¦ ¦ anti- ¦with V sub R > 85 kt.
ISO Type II¦& polymeric¦ ¦ icing ¦Lower viscosity than ¦thickeners ¦ High ¦ ¦AEA Type II ¦ ¦ ¦ ¦produced before ¦ ¦ ¦ ¦1988.
___________¦___________¦_________¦________¦______________________ Old Mil ¦ Ethylene, ¦ Low ¦ ¦ Type I ¦ propylene ¦ ¦ ¦No fire inhibitor.
¦ glycol ¦ ¦Deicing ¦May not conform to SAE New Mil ¦Propylene ¦ Med ¦ ¦Type I Spec. See AC
Type I ¦glycol base¦ ¦ ¦20-117 for more detail ___________¦___________¦_________¦________¦______________________ Old Mil ¦Ethylene & ¦ ¦ ¦With fire inhibitor.
Type II ¦ propylene ¦ Low ¦Deicing ¦Does not conform to & ¦ glycol ¦ ¦ ¦SAE Type II Spec.
New Mil ¦ ¦ ¦ ¦See AC 20-117 for more Type II ¦ ¦ ¦ ¦detail ___________¦___________¦_________¦________¦______________________ Arktika ¦ ¦ Low ¦Deicing ¦Not currently approved ¦ Ethylene ¦ ¦ ¦as AEA, SAE, or ISO Arktika 200¦ glycol ¦ ¦ ¦Type I or Type II.
¦ & ¦ High ¦ Anti- ¦Effects on ¦ thickeners¦ ¦ Icing ¦Aerodynamics unknown.
¦ ¦ ¦ ¦Prevalent in Russia ___________¦___________¦_________¦________¦______________________ * Beginning with the 1993-1994 winter season, North American manufacturers intend to no longer produce AMS1425 and AMS1427 in favor of the new AMS1424.
---------------------------------------------------------------- Traditional North American Fluids As shown in table 1, there are various types of FPD's available.
These fluids are produced by chemical manufacturers in North America and Europe. The FPD's used to deice aircraft in North America are usually composed of ethylene or propylene glycol combined with water and other ingredients. Users can purchase this deicing fluid in a concentrated form (80 percent-90 percent glycol) or in a solution that is approximately 50 percent glycol with 50 percent water by volume.
ISO Commercial Fluids These fluids were originally known as AEA Type I and Type II.
Specifications for these two types of FPD's are provided in the ISO guidelines as ISO 11075, "Aircraft deicing/anti-icing Newtonian fluids ISO Type I" and ISO 11078, "Aircraft deicing/anti-icing non-Newtonian fluids ISO Type II."
SAE Commercial Fluids.
SAE Type I and Type II fluids are very similar in all respects to ISO Type I and Type II fluids. The minor differences will not be presented in this AC. These FPD's, specified by the SAE and ISO as Type I and Type II, are distinguished by material requirement, freezing point, rheological properties (viscosity and plasticity), and anti-icing performance.
SAE and ISO Type I Fluids.
These fluids in the concentrated form contain a minimum of 80 percent glycols and are considered "unthickened" because of their relatively low viscosity. These fluids are used heated and diluted for deicing or anti-icing, but provide very limited anti-icing protection.
SAE and ISO Type II Fluids.
These fluids contain a minimum of 50 percent glycols and are considered "thickened" because of added thickening agents that enable the fluid to be deposited in a thicker film and to remain on the aircraft surfaces until the time of takeoff. These fluids are used for deicing and anti-icing, and provide greater protection than do Type I fluids against ice, frost, or snow formation in conditions conducive to aircraft icing on the ground.
SAE and ISO Type II fluids are designed for use on aircraft with V sub R greater than 85 knots. As with any deicing or anti-icing fluid, SAE and ISO Type II fluids should not be applied unless the aircraft manufacturer has approved their use regardless of rotation speed. SAE and ISO Type II fluids are effective anti-icers because of their high viscosity and pseudoplastic behavior. They are designed to remain on the wings of an aircraft during ground operations or short term storage, thereby providing some anti-icing protection, but to readily flow off the wings during takeoff. When these fluids are subjected to shear stress, such as that experienced during a takeoff run, their viscosity decreases drastically, allowing the fluids to flow off the wings and causing little adverse effect on the aircraft's aerodynamic performance.
The anti-icing effectiveness of SAE and ISO Type II fluids is dependent upon the pseudoplastic behavior which can be altered by improper deicing/anti-icing equipment or handling. Some of the North American airlines have updated deicing and anti-icing equipment, fluid storage facilities, deicing and anti-icing procedures, quality control procedures, and training programs to accommodate the distinct characteristics of SAE and ISO Type II fluids. Testing indicates that SAE and ISO Type II fluids, if applied with improper equipment, may lose 20 percent to 60 percent of anti-icing performance.
SAE and ISO Type II fluids have been in the process of introduction in North America since 1985. Widespread use of SAE and ISO Type II fluids began to occur in 1990. Similar fluids, but with slight differences in characteristics, have been developed, introduced, and used in Canada.
Military Deicing Fluids The U.S. Department of Defense has issued military specifications, "Anti-Icing and Deicing-Defrosting Fluids."
These documents specify specified the following types of FPD's:
* MIL-A-4823C Type I - standard * MIL-A-4823C Type II - standard with inhibitor * MIL-A-4823D Type I (propylene glycol base) * MIL-A-4823D Type II (ethylene and propylene glycol mix) Military Types I and II fluids are essentially the same, except that Military Type II fluids contain a fire inhibitor. Military Types I and II fluids are unrelated to SAE and ISO Types I and II fluids.
SAE Type III Fluids.
Specifications for fluids for use on small aircraft which would last longer but yet would have minimal aerodynamic effect, are being developed. These fluids are referred to as Type III fluids. Fluids of this type have been developed and used to a limited extent, in large airplane operations, and have generally been referred to as Type I 1/2 fluids as they possess characteristics in between Type I and Type II; i.e., last longer than Type I with less aerodynamic effect than Type II.
Use of Antifreeze and Unapproved Fluids Use FPD fluids that are approved for use by the aircraft manufacturer. Some fluids may not be compatible with aircraft materials and finishes and some may have characteristics that impair aircraft performance and flight characteristics or cause control surface instabilities. Use of automotive anti-freeze is NOT approved. Its time of effectiveness (holdover time) and its effects on aircraft aerodynamic performance is generally unknown.
CHARACTERISTICS OF FPD FLUIDS Chemical Composition of FPD Fluids Commercially available FPD fluids are of the ethylene glycol, diethylene glycol, or propylene glycol family. The exact formulas of various manufacturers' fluids are proprietary. It is important to understand that some commercially available FPD fluids contain one or more of these glycols plus small quantities of additives and water. Various FPD manufacturers, upon request, will premix aqueous solutions of FPD for specific customer reasons. Before using a solution of FPD, it is imperative that the ingredients be checked by close examination of the stock number and by a quality control examination to ascertain that the fluid supply conforms to the user need. FPD fluid manufacturers can supply methodology and suggest equipment needed for quality control examinations. It is desirable that the pilot understand the criticality of effective quality control.
Freezing Characteristics of FPD Fluids Before a fluid is used on an aircraft, it is crucial that the user knows and understands its freezing characteristics. These characteristics can be determined through understanding of the fluid procurement specifications and tolerances and through quality control inspections. FPD fluids are either premixed (diluted with water) by the manufacturer or mixed by the user from bulk supplies. To ensure known freezing characteristics, samples of the final mixture should be analyzed before use.
FPD Fluid Strength When Applied Fluid strength or the ratio of FPD ingredients, such as glycol, to water should be known if proper precautions, such as those outlined above, are taken before application. It is crucial to
realize that fluid strength is a significant factor in deicing and anti-icing properties. Fluid strength affects the time that the FPD fluid may remain effective (holdover time).
Tables 1-2 and 1-4, Appendix A, present guidelines for estimated holdover times of SAE and ISO Type II and SAE and ISO Type I fluids respectively as a function of weather conditions and OAT.
Do not use pure (100 percent) ethylene glycol or pure propylene glycol fluids in nonprecipitation conditions. The reasons for this caution are explained below.
* The freezing point of pure ethylene glycol is much higher than when diluted with water. Slight temperature decreases can be induced by factors such as cold-soaked fuel in integral tanks, reduction of solar radiation by clouds obscuring the sun, ambient temperature cooling, wind effects, and lowered temperature during development of wing lift. If the freezing point of the remaining film is found to be insufficient, the deicing/anti-icing procedure should be repeated before the aircraft is released for flight.
* Full strength (undiluted) propylene glycol, having a strength of about 88 percent glycol at temperatures less than -10 degrees C (+14 degrees F), is quite viscous. In this form, propylene glycol based fluids have been found to produce lift reductions of about 20 percent. Propylene glycol FPD fluids are not intended to be used in the undiluted state.
TEMPERATURE BUFFER American Practice The practice developed and accepted by the North American air carrier industry using traditional North American fluids is to ensure that the remaining film has a freeze point of at least 20 degrees F below (lower than) ambient temperature.
European and Canadian Practice The practice developed by the European air carrier industry has been to ensure that the freezing point of residual SAE and ISO Type I fluids is at least 10 degrees C (18 degrees F) below ambient temperature. This is similar to the North American practice, except for metric conversion differences. For SAE and ISO Type II fluids, the freeze temperature should be at least 7 degrees C (13 degrees F) below ambient temperature. This temperature difference between SAE and ISO Type I and SAE and ISO Type II FPD fluids is primarily to accommodate differences in fluid dilution rates which occur in freezing precipitation. Type II fluids, which are thicker, will not dilute to the same extent in a given period of time.
Current FAA Recommendations Generally the holdover time is increased with an expansion of the
temperature buffer. Therefore, if the choice is available, use the maximum buffers. Greater buffers require the use of more glycol, which is more costly and which increases the burden for collection and processing of FPD spillage and runoff. FPD fluid mixtures and their attendant buffers should be determined after consideration of the following factors in the listed order of priority.
* Safety * Availability * Environmental impact * Cost For traditional North American and AEA, SAE and ISO Type I Fluids, the freeze point buffer of the anti-icing fluid should be as great as possible but not less than 10 degrees C (18 degrees F).
For AEA, SAE and ISO Type II Fluids, the freeze point buffer should not be less than those recommended by the SAE and ISO which is currently 7 degrees C (13 degrees F) at ambient temperatures below -7 degrees C (19 degrees F) and 3 degrees C (5 degrees F) at ambient temperatures above -7 degrees C (19 degrees F).
AC 20-117 Recommendation The FAA's recommendation, published in AC 20-117 is to ensure that the fluid freeze point is at least 20 degrees F (11 degrees C) below the colder of the ambient or aircraft surface (skin) temperature. The reasons for this differential are to delay refreezing of the anti-icing fluid and to take into consideration such factors as:
* Temperature reduction during climb or in the production of aerodynamic forces, and the possibility that residual fluids (on surfaces, in balance bays, etc.) will freeze at attitude;
* Freezing potential in conditions conducive to icing. As freezing precipitation or moisture from any source contacts and is absorbed by the residual anti-icing fluid, the freeze point is increased. A greater temperature buffer provides a longer holdover time due to this effect; and * Quality control margin for error.
HOLDOVER TIMES Holdover Time. For Part 135 operators that do not have an approved deicing/anti-icing program (under Section
135.227(b)(3)), which complies with Section 121.629(c), the use of holdover timetables is for use in departure planning only.
The use of holdover times for these Part 135 operators does not relieve the pilot from conducting a pretakeoff contamination check. For Part 135 operators that have an approved deicing/anti-icing program (under Section 135.227(b)(3)), they
must follow the appropriate Part 121 procedures.
Holdover time is the estimated time deicing/anti-icing fluid will prevent the formation of frost or ice and the accumulation of snow on the protected surfaces of an aircraft.
Holdover time begins when the final application of deicing/antiicing fluid commences and expires when the deicing/anti-icing fluid applied to the aircraft loses its effectiveness.
Holdover time tables are based on fluid type, fluid concentration, outside air temperature (OAT) and various weather conditions, e.g., frost, freezing fog, snow, freezing rain.
SAE/ISO holdover tables and how they are used are explained in Appendix A.
Many other variables may affect holdover times, some of these include:
* Aircraft surface (skin) temperature;
* Operation in close proximity to other aircraft, equipment, and structures;
* Operation on snow, slush, or wet ramps, taxiways, and runways;
* Precipitation rate;
* Relative humidity;
* Wind velocity and direction.
DEICING AND ANTI-ICING PROCEDURES Depending on the type of accumulation on the surfaces and components of the aircraft and the type of aircraft, operational procedures employed in aircraft ground deicing and anti-icing vary.
Ground deicing and anti-icing procedures vary depending primarily on aircraft type, type of ice accumulations on the aircraft, and FPD fluid type. All pilots should become familiar with the procedures recommended by the aircraft manufacturer in the Aircraft Flight Manual (AFM) or the maintenance manual and, where appropriate, the aircraft service manual.
The general procedures used by aircraft operators are similar and are based on the procedures recommended by the aircraft manufacturer, which, in turn, may be based upon procedures recommended by the fluid manufacturer, engine manufacturer, the SAE, ISO, AEA, and other standardization organizations.
CAUTION: If improperly used, some deicing/anti-icing fluids can cause undesirable and potentially dangerous changes in aircraft performance, stability, and control. In addition, the fluid may not remain effective for the expected time.
Ice, snow, frost, and slush should be removed before takeoff.
Any frozen contamination may be removed by placing the aircraft in a heated hangar or by other normal deicing procedures.
Frost, including underwing frost in the vicinity of integral fuel tanks should be removed before takeoff. On some small aircraft frost formations may be polished smooth. Underwing frost may be allowed on some aircraft if the aircraft manufacturer has underwing data accepted by the FAA Aircraft Certification Office showing that the aircraft can be operated safely under such conditions.
Dry, powdery snow can be removed by sweeping with an appropriate brush or broom or by blowing cold air or nitrogen gas or other inert gasses across the aircraft surface. Heavy, wet snow can be removed by mechanical means such as squeegees and brooms, by using heated water, solutions of heated water and deicing/anti-icing fluids, or a combination of these techniques.
Any frozen contamination may be removed by placing the aircraft in a heated hangar or by other normal deicing procedures.
Deicing and anti-icing aircraft with fluids An aircraft must be systematically deiced and anti-iced in weather conditions conducive to icing. The specific deicing method and procedure used depends upon the aircraft type, available equipment, and the deicing/anti-icing fluids available.
Aircraft operating under FAR 135 and other small airplanes may not be permitted to use or have available some of the modern deicing/anti-icing fluids. Each aircraft surface requires a specific technique to achieve a clean aircraft.
The wings are the main lifting surfaces of the aircraft and must be free of contaminants to operate efficiently. An accumulation of upperwing frost, snow, or ice changes the airflow characteristics over the wing, reduces its lifting capabilities, increases drag, increases stall speed, and changes pitching moments. The weight increase is slight, and weight effects are secondary to the effects of surface roughness.
On most aircraft, deicing of the wing should begin at the leading-edge wing tip, sweeping in the aft and inboard direction.
This process avoids increasing the snowload on outboard wing sections, which under some very heavy snow conditions could produce excessive wing stresses. This method also (for most aircraft) reduces the possibility of flushing ice or snow deposits into conventional balance bays and cavities.
If ice accumulation is present in areas such as flap tracks and control cavities, it may be necessary to spray from the trailing edge forward. Also, under some weather (wind) or ramp conditions, it may be necessary to spray from the trailing edge.
Propellers should be thoroughly deiced in the static mode assuring that all blades are uniformly clean.
The extendible surfaces of the wing (i.e., leading-edge flaps or slats and trailing-edge flaps) should be retracted to avoid accumulating frost, snow, or ice during time at the gate or in overnight storage. A surface that is extended in weather conditions requiring deicing and anti-icing should be visually
inspected to ensure that the surface, tracks, hinges, seals, and actuators are free of any contaminants before retraction. Flaps and slats retracted during anti-icing will not receive a protective film of FPD fluid and may freeze in precipitation or frost conditions. Consult the AFM, AOM, or Maintenance Manual for recommended procedures to determine the most appropriate slat and flap management procedures.
Tail surfaces require the same caution afforded the wing during the deicing procedure. The balance bay area between moveable and stationary tail surfaces and areas adjacent to balance horns should be closely inspected. For some aircraft, positioning the horizontal stabilizer in the leading-edge-down position allows the FPD fluid and contaminants to run off rather than into balance bays. For some aircraft, the horizontal stabilizer must be in the leading-edge-up position during deicing. Some aircraft, with fixed or movable horizontal stabilizer, may require the elevator to be in a preset position.
Balance bays, control cavities, and gap seals should be inspected to ensure cleanliness and proper drainage. When contaminants do collect in the surface juncture, they must be removed to prevent the seals from freezing and impeding the movement of the control surface.
The fuselage should be deiced and anti-iced from the top down.
Clearing the top of the fuselage manually instead of by spraying also requires that personnel use caution not to damage protruding equipment (e.g., antennas) while deicing. Spraying the upper section with heated FPD fluid first allows the fluid to flow down, warming the sides of the fuselage and removing accumulations. This is also effective when deicing the windows and windshield of the aircraft, since direct spraying of the surfaces can cause thermal shock resulting in cracking or crazing of the windows. The FPD fluid must be removed from the flight crew's window to maintain optimal visibility.
Deicing the top of the fuselage is especially important on aircraft with aft-mounted centerline and aft-side fuselage mounted engines. The ingestion of ice or snow into a turbine engine may result in compressor stalls or damage to the engine.
The nose of the aircraft (radome area on some aircraft) should be deiced to eliminate snow or ice accumulations from being projected into the crew's field of vision during takeoff. This area may also contain navigation and guidance equipment; and if so, it must be cleared of accumulations to ensure proper operation of these sensors.
Also, special precautions are necessary to ensure that residual fluids do not enter sensitive instrumentation or flow over the cockpit windows during taxi or takeoff.
Cargo and passenger doors must also be deiced and anti-iced in order to ensure proper operation. All hinges, tracks, and seals should be inspected to ensure that they are free of contamination. Frozen contamination may also cause damage and