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 and ISO. Tables 3 and 4 in appendix 1 relate guidance suggested by the SAE based upon SAE and ISO recommendations.
Pilot training can be accomplished through the use of manuals, films, and, to a limited extent, onsite observation. It is essential that the PIC fully understand effective deicing and anti-icing procedures. An annual review of these procedures by all pilots is required to maintain current knowledge of deicing and anti-icing methods, since the PIC is responsible for ensuring that critical aircraft surfaces are free from ice, snow, or frost formations before takeoff. An aircraft may be deiced by any suitable manual method, using water, FPD fluids, or solutions of FPD fluids and water. Heating these fluids increases their deicing effectiveness; however, in the anti-icing process, unheated fluids are more effective. SAE and ISO Type Il fluids are more effective for providing anti-icing protection than are traditional North American fluids and SAE and ISO Type I fluids.
Deicing and anti-icing may be performed as a one-step or two-step process, depending on predetermined practices, prevailing weather conditions, concentration of FPD used, and available deicing equipment and facilities.
The one-step procedure is accomplished using a heated or, in some cases, an unheated FPD mixture. In this process, the residual FPD fluid film provides a very limited anti-icing protection. This protection can be enhanced by the use of cold fluids or by the use of techniques to cool heated fluid during the deicing process. A technique used commonly in the past is to spray on a final coat of deicing fluid using a very fine mist, applied in an arched trajectory so as to cool the fluid before contact. This produces a thicker fluid film which will have slightly enhanced anti-icing effectiveness. Exercise caution when using this technique to ensure that freezing has not occurred within the fluid previously applied.
The two-step procedure involves both deicing and anti-icing.
Deicing is accomplished with hot water or a hot mixture of FPD and water. The ambient weather conditions and the type of accumulation to be removed from the aircraft must be considered 22
when determining which deicing fluid to use. The second (anti-icing) step involves applying a mixture of SAE or ISO Type Il and water to the critical surfaces of the aircraft.
When heated water alone is used in the deicing process, the second step must be performed before refreezing occurs--generally within 3 minutes after the beginning of the deicing step. If necessary, the process is conducted area-by-area. As with any deicing or anti-icing fluid, SAE and ISO Type Il fluid should not be used unless the aircraft manufacturer has approved its use. SAE and ISO Type Il fluids are designed for use on aircraft with Vp in excess of 85 knots.
This is to ensure sufficient flowoff of the fluid during the takeoff.
Table 3, appendix 1, contains recommendations developed by SAE and ISO.
Under no circumstances should SAE and ISO Type Il fluids, in the concentrated (neat) form, be applied to the following areas of an aircraft:
Pitot heads and angle-of-attack sensors;
Control surface cavities;
• Cockpit windows and nose of fuselage;
• Lower side of radome underneath nose;
Static ports;
Air inlets; and
• Engines.
The freezing point of residual fluids on aircraft surfaces resulting from FPD fluids mixing with precipitation or melted ice should oe at least the values presented in tables 3 and 4, appendix 1. FPD treezing points can be determined by using a refractometer or other similar techniques.
RECOMMENDED USE OF
DEICING/ANTI-ICING CODES Following ground deicing, anti-icing, and inspection by qualified personnel, information supplied to the flightcrew should include the 23
type of final fluid coating applied, the mixture of fluid (percent by volume), and time of application. This may be transmitted to the pilot by a four element code, such as the following.
Element A specifies Type I or Type Il fluid;
Element B specifies the percentage of fluid within the fluid/ water mixture (e.g., 75/25 = 75 percent fluid and 25 percent water);
Element C specifies the local time of the beginning of the final deicing/anti-icing step (e.g., 1330); and Element D specifies date (day, written month, year)
(e.g., 20 April 1992).
These elements are recommended for use in recordkeeping, and are optional for flightcrew notification.
Examples of the Deicing/Anti-icing Information Format are as follows:
Type Il - 100/0 - 1100h - 16 Mar 1991 Type II - 75/25 - 1330h - 20 Apr 1992 Type I - 70/30 - 0942h - 17 Feb 1992
DEICING OF AIRCRAFT SURFACES An aircraft must be systematically deiced and anti-iced in weather conditions conducive to icing (figure 2). 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, reducing its lifting capabilities, increasing drag, increasing stall speed, and changing pitching moments. The weight increase is slight, and its effects are secondary to those caused by surface roughness.
Figure 2. Systematic Deicing of Aircraft in Conditions Conducive to Icing 25
On most aircraft, deicing of the wing should begin at the leadingedge 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 reduces the possibility of flushing ice or snow deposits into the 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 or ramp conditions, it is necessary to spray from the trailing edge.
The extendable surfaces of the wing (i.e., leading-edge 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 aircraft manufacturer to ascertain the most appropriate slat and flap management procedures.
The tail surfaces require the same caution afforded the wing during the deicing procedure. The balance bay area between moveable and stationary tail surfaces 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.
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 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, 26
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 crew's windows to maintain optimal visibility.
Deicing the top of the fuselage is especially important on aircraft with aft-mounted centerline and fuselage mounted engines. The ingestion of ice or snow into an engine may result in compressor stalls or damage to the engine.
The radome or nose of the aircraft should be deiced to eliminate snow or ice accumulations from being projected into the crew's field of vision during takeoff. This area also contains navigation and guidance equipment; therefore, 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.
The cargo and passenger doors must also be deiced and anti-iced in order to ensure proper operation. All hinges and tracks should be inspected to ensure that they are free of accumulation. Although accumulation may not impair operation on the ground, it may freeze at flight altitude and prevent normal operation at the aircraft's destination. Frozen accumulation may also cause damage and leakage on cargo and passenger door hatches.
Sensor orifices and probes along the fuselage require caution during the application of FPD fluid. Direct spraying into these openings and resulting fluid residue can result in faulty instrument readings. Also, when protective covers used during applications are not removed, faulty instrument readings can result.
DEICING THE ENGINE AREA Minimal amounts of FPD fluid should be used to deice the engine area and APU. FPD fluids ingested in the APU can cause smoke and vapors to enter the cabin. Engine intake areas should be inspected for the presence of ice immediately after shutdown. Any accumulation should be removed while the engine is cooling and before installation of plugs and covers. Any accumulation of water must be removed to prevent the compressor from freezing. A light coating of deicing fluid applied to the plug may prevent the plugs from freezing to the nacelle.
Fluid residue on engine fan or compressor blades can reduce engine performance or cause stall or surge. In addition, this could increase the possibility of, or the quantity of, glycol vapors entering the aircraft through the engine bleed air system.
Most turbojet and turboprop engine manufacturers recommend, and some AFM's require, that thrust levers be periodically advanced to an N1 rpm of 70 percent to 80 percent during ground operations.
This practice prevents ice buildup that can result in reduced thrust, dynamic imbalance of the fan or compressor, or excessive induction of shed ice. The pilot must be aware of these operating procedures and should comply with procedures established for the aircraft.
CLEAR ICE PHENOMENA Some aircraft have experienced formations of clear ice on the upper surfaces of wings in the vicinity of integral fuel tanks. Such ice is difficult to see and in many instances can not be detected other than by touch with the bare hand or by means of special purpose ice These phenomena typically occur on aircraft that have flown high altitude missions for a sufficient time to cold soak the fuel in tanks, and the fuel remaining in wing tanks at the destination is sufficient to contact upper wing skins when rain or high humidity is present. Upperwing frost can also occur under conditions of high relative humidity.
In either case, ice or frost formation on upper wing surfaces must be removed prior to takeoff. Skin temperature should be increased to preclude formation of ice prior to takeoff. This is often possible by refueling with warm fuel.
Clear ice formations of this type can cause aircraft performance changes and can break loose at rotation or during flight, causing engine damage on some aircraft types, primarily those with rear mounted engines.
CENTRAL AND REMOTE DEICING Deicing and anti-icing near the departure end of the runway has obvious advantages. This practice:
• Reduces the time between deicing/anti-icing and takeoff;
• Facilitates the recycling of FPD in the deicing mixture;
• Reduces the potential environmental impact; and
• Facilitates the application of correct ratio FPD/water for existing environmental conditions at departure.
This practice is encouraged where adequate facilities exist and if performed by qualified personnel. It should not be substituted for a pretakeoff check unless performed just prior to takeoff.
TECHNIQUES FOR IMPLEMENTING THE
CLEAN AIRCRAFT CONCEPT
• Establish training programs to continually update pilots on the hazards of winter operations, adverse effects of ice formations on aircraft performance and flight characteristics, proper use of ice protection equipment, ground deicing and anti-icing procedures, deicing and pretakeoff procedures following ground 29
deicing or anti-icing, and operations in conditions conducive to aircraft icing.
• Establish training programs for maintenance or other personnel who perform aircraft deicing to ensure thorough knowledge of the adverse effects of ice formations on aircraft performance and flight characteristics, critical components, specific ground deicing and anti-icing procedures for each aircraft type, and the use of ground deicing and anti-icing equipment including detection of abnormal operational conditions.
• Establish quality assurance programs to ensure that FPD fluids being purchased and used are of the proper characteristics, that proper ground deicing and anti-icing procedures are utilized, that all critical areas are inspected, and that all critical components of the aircraft are clean prior to departure.
• Perform thorough planning of ground deicing activities to ensure that proper supplies and equipment are available for forecast weather conditions and that responsibilities are specifically assigned and understood. This is to include maintenance service contracts.
Monitor weather conditions very closely to ensure that planning information remains valid during the ground deicing or anti-icing process and subsequent aircraft operations. Type or concentration of FPD fluids, deicing or anti-icing procedures, and departure plans should be altered accordingly.
Deice or anti-ice areas that are visible from the cockpit first so that during pretakeoff check the pilot may have assurance that other areas of the aircraft are clean. Areas deiced or anti-iced first will generally freeze first.
• Use the two-stage deicing process where ice deposits are first removed, and secondly all critical components of the aircraft are coated with an appropriate mixture of FPD fluid to prolong the effectiveness of the anti-icing.
• Ensure thorough coordination of the ground deicing and antiicing process so that final treatments are provided just prior to takeoff.
• When feasible, provide and use remote sites near the takeoff position for deicing, anti-icing, final inspection, and to reduce the time between deicing and takeoff.
• Use multiple aircraft deicing or anti-icing units for faster and more uniform treatment during precipitation.
• 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.
• Do not use substances that are approved for use on pneumatic boots (to improve deicing performance) for other purposes unless such uses are approved by the aircraft manufacturer.
• Use FPD fluid types and concentrations that will delay ice formations for as long as possible under the prevailing conditions.
Appendix 1 PPENDIX 1
APPLICATION GUIDELINES TABLES This appendix contains guidelines (in tabular format) for the application of Type I and Type II FPD fluids and advisory material on holdover times. These tables were developed by the SAE ad hoc committee on Aircraft Ground Deicing in conjunction with the ISO committee on ®Aerospace Aircraft Deicing and Anti-icing Methods With Fluids.i This information will continue to be refined as additional data is acquired. These guidelines should only be used by air carriers as a part of, or in conjunction with, an approved ground deicing/anti-icing program.
Appendix 1 Table 1. Guidelines for Holdover Times Anticipated by SAE Type Il and ISO Type Il Fluid Mixtures as a Function of Weather Conditions and OAT.
CAUTION! THIS TABLE IS FOR USE IN DEPARTURE PLANNING ONLY AND IT
SHOULD BE USED IN CONJUNCTION WITH PRETAKEOFF CHECK PROCEDURES.
OAT Type Il Fluid Approximate Holdover Times Anticipated Under Concentration Various Weather Conditions (hours: minutes) Neat- °C of Fluid/Water FROST FREEZING SNOW FREEZING RAIN ON 1% by FOG RAIN COLD SOAKED Volume! WING 100/0 12:00 1:15-3:00 0:25-1:00 0:08-0:20 0:24-1:00 32 and and 75/25 6:00 0:50-2:00 0:20-0:45 0:04-0:10 0:18-0:45 above above 50/50 4:00 0:35-1:30 0:15-0:30 0:02-0:05 0:12-0:30 below below 100/0 8:00 0:35-1:30 0:20-0:45 0:08-0:20 CAUTION!
32 75/25 5:00 0:25-1:00 0:15-0:30 0:04-0:10 clear ice may to to require touch for -7 19 50/50 3:00 0:20-0:45 0:05-0:15 0:01-0:03 confirmation below below 100/0 8:00 0:35-1:30 0:20-0:45 19 to to 75/25 5:00 0:25-1:00 0:15-0:30
• 14 7 below below
- 14 7 100/0 8:00 0:35-1:30 0:20-0:45 to -25 -13 bolow balow 100/0 if 7°C (13°F) A buffer of at least 7°C (13°F) must be maintained for Type Il used for -25 - 13 Buffer is maintained anti-icing at OAT below -25°C (-13°F). Consider use of Type I fluids where SAE or ISO Type Il cannot be used.