Chapter 10 - Preventative Measures and De/Anti-Icing Procedures
- 10.1 Introduction
- 10.2 Preventive Measures
- 10.3 Fluid Application Procedures
- 10.4 Procedures Selection
- 10.5 No Spray Zones
- 10.6 Fluid Application
- 10.7 Fluid Dry Out
- 10.8 Deicing and Anti-icing Fluid Compatibility
- 10.9 Blending TypeI Fluids
- 10.10 Using TypeIV Fluid to Prevent Frost Formation Overnight
- 10.11 Applying TypeIV Fluid in a Hangar
- 10.12 Manual Methods
- 10.13 Technology Options
Specific rules set forth by the Canadian Aviation Regulations (CARs) require that: "No person shall conduct or attempt to conduct a take-off in an aircraft that has frost, ice or snow adhering to any of its critical surfaces".
10.2 Preventive Measures
A good method of ensuring that an aircraft is clean of contamination is by preventing the contamination from collecting in the first place; that is, park the aircraft in a hanger. Availability of space, particularly for larger aircraft is a major obstacle with respect to the use of hangars on a routine basis.
If precipitation is present, care must be taken to reduce the skin temperature to below freezing prior to taking the aircraft from the hanger. This can be accomplished by opening the hanger doors prior to rolling the aircraft out. This of course will impact on the users of the hanger. Depending on the facility, it may be possible to apply anti-icing fluids prior to departing the hanger.
Parking a fully or partially fuelled aircraft in a heated hangar presents special considerations. The temperature of the fuel will gradually rise towards the ambient temperature of the hangar. When the fuel is in contact with the upper surface of the wing, the wing surface will assume the temperature of the fuel; so cooling the wing surface by opening the hangar doors is less effective. This temperature effect will be present for an extended time period while the fuel cools once the aircraft is exposed to the outside temperature. When precipitation is present, the warm surface can cause snow and sleet to warm and stick to the wing or to melt. In this instance the application of deicing/anti-icing fluids may be the only effective solution. Possibly, under these circumstances, the aircraft should not be hangared with significant volumes of fuel in wing tanks.
Once an aircraft is contaminated, if a heated hanger is available, the heat and shelter from the elements will greatly help the removal of contamination. This will take time but if available greatly reduces the amount of deicing fluid required.
10.2.2 Wing covers
Many operators of smaller aircraft have found wing covers to be an effective way to prevent the build up of contamination on wings. Wing covers, although effective, have some drawbacks. Extreme care is required in both installation and removal of the covers in order to avoid damage to the aircraft. Depending on the aircraft type, ladders or a similar device are required during installation and removal of covers; and in inclement weather safety is a concern when climbing ladders due to the possibility of slipping. Installing covers on wings that are already contaminated often leads to problems. One other drawback of wing covers is the requirement for a large area to store the covers and allow them to dry (i.e. a place to hang them). There have also been problems of wings "sweating" while covered, and then having the covers freeze to the wings.
10.3 Fluid Application Procedures
SAE document ARP4737, fluid manufacturers recommendations, and the aircraft maintenance manual should be consulted in establishing sound operational de/anti-icing procedures.
The deicing/anti-icing operation should be performed as close in time to the takeoff procedure as possible. This generally means that the location chosen on an airport for deicing should be as near to the end of the operational runway as is possible.
De/anti-icing near the beginning of departure runways reduces the interval between the anti-icing process and take off. It is this interval that determines whether takeoff can be achieved prior to fluid failure. Once the fluid has failed, the aircraft must be de/anti-iced again. Under no circumstances shall a second application of anti-icing fluid be applied over a contaminated anti-icing fluid layer.
Research has indicated that if the fluid is not applied correctly, the HOT Guideline values are not achievable.
NOTE: TypesII, & IV fluids, in particular, must be applied using specialized equipment. If these fluids are not applied in the correct manner and with the correct equipment, as recommended by the fluid manufacturer, they will NOT function as designed and will therefore NOT provide the expected protection as indicated in the HOT tables.
Preliminary information on TypeIII fluids, suggests that the use of older TypeI application equipment with TypeIII fluids could present a problem. There is a concern that the older TypeI equipment may overheat the TypeIII fluid and adversely affect its long-term stability and HOT performance. The fluid manufacturer must be contacted for specific application recommendations pertinent to TypeIII fluids.
10.4 Procedure Selection
Fluid application procedures from SAE ARP4737 Caution and Fluid Application Reminder, are outlined in the Table entitled: "TypeI Deicing Fluid Application Procedures for TypeI fluids", and in the Table entitled: "SAE TypeII/IV Anti-Icing Fluid Application procedures" for TypesII, III and IV fluids, at the Transport Canada HOT website.
Depending on the prevalent weather conditions, available equipment, technology, fluids and the desired holdover time, a one step or a two step de/anti-icing procedure may be appropriate. The aircraft must be treated symmetrically for aerodynamic reasons, as recommended in SAE ARP4737.
Individual aircraft manufacturers provide guidance on specific anti-icing or deicing procedures for their particular aircraft models. An Air Operator must obtain and follow the aircraft manufacturers' guidance.
It is also necessary for the Air Operator to understand aircraft deicing and anti-icing standard practices, such as those published in SAE ARP4737. The Regulations, Standards and Guidance published by Transport Canada must also be followed.
The effectiveness of anti-icing fluid in protecting the aircraft's critical surfaces from the adherence of frozen contaminants is dependant upon the correct execution of the deicing process. The proper procedures and equipment must be employed to ensure that when both deicing and anti-icing have been accomplished the aircraft is safe for take off. This assurance requires that a thoroughly qualified and trained deicing crew accomplish the tasks.
The temperature of cold soaked wings can be considerably below the ambient temperature; therefore frost can build up in localized areas. When active frost is anticipated, SAE TypeII or IV may be applied to the surfaces to prevent frost accumulation. Both wings should receive a symmetrical treatment for aerodynamic reasons.
NOTE: The following guidance is general in nature and is not intended to be fluid manufacturer specific.
10.4.1 One-Step Deicing/Anti-icing
Generally, in Canada the use of a one step process suggests that there isn't any active precipitation occurring at the time of deicing. However, in Europe the one step method is used with TypeII & Type IV anti-icing fluids in a diluted and heated state, and applied with a specialized nozzle. Also, in Canada's Northern communities, given the extremely low temperatures, the only fluid option has been the TypeI fluids, and a one step procedure is sometimes used despite the associated short Hold Over Times.
The thickened fluids, TypesII, III & IV, should not be used unheated on an aircraft contaminated with any snow, ice or frost. The aircraft surfaces must first be cleaned before application of an unheated fluid.
10.4.2 Two Step Deicing/Anti-icing
Two step deicing/anti-icing is generally used when the aircraft is contaminated and when precipitation is active.
If a two step procedure is used, the first step is typically performed using a deicing fluid; however, alternate deicing technology or mechanical methods may be used depending upon circumstances. The selection of fluid type and concentration depends on the ambient temperature, the weather conditions and the desired holdover time. When performing a two-step process, the freezing point of a fluid used for the first step must not be less than 3°C above ambient temperature. The freezing point of a SAE TypeI fluid used for one-step or as the second step of the two-step operation must be at least 10°C below the ambient temperature. The second step must be completed as quickly as possible following first step fluid application (not more than 3 minutes). The two step process may need to be performed area by area. When deicing fluid is used in step1, the application of the second step fluid will flush away the first step fluid and leave a film of anti-icing fluid which, is designed to be of adequate thickness. If freezing of the deicing fluid has occurred, step 1 must be repeated. Refer to SAE ARP4737 document for additional details.
SAE TypeI fluids have limited effectiveness as an anti-icing fluid due to their short holdover time. SAE TypeII, III, or IV fluids used as deicing/anti-icing agents may have a temperature application limit of -25°C. The application limit may be lower provided a 7°C buffer between the freezing point and the ambient temperature is maintained and the fluid has been demonstrated to be aerodynamically acceptable at this ambient temperature.
Apply heated ADF until all of the frozen contaminants have been removed from the aircraft's critical surfaces. The ADF fluid is typically heated so that it will arrive at the application nozzle at around 60-82°C (140-180°F).
No frozen contaminants shall remain after application of an ADF, including under the fluid.
Aircraft surfaces should be treated symmetrically for aerodynamic reasons.
Apply the AAF to aircraft surfaces before any freezing of the ADF occurs. Typically the application of AAF should occur within 3 minutes of deicing with a heated ADF.
See the applications section for further considerations in the application of the fluids.
10.5 No Spray Zones
Operators need to clearly understand where they can or cannot spray de/anti-icing fluids.
Examples of no spray zones include, but are not limited to:
- Engine inlets and openings;
- APU inlets;
- Engine exhaust openings;
- Aircraft brakes;
- Flight deck windows;
- Cabin windows;
- Passenger door handles;
- Static ports;
- Pitot heads;
- Air data sensors;
- Avionics vents; and
- Aircraft manufacturer specified "no spray" areas.
The various aircraft types that will be de-iced at a station need to be identified. The operators must be very familiar with any unique deicing considerations based upon aircraft type.
10.6 Fluid Application
10.6.1 Spray Pressure
During the deicing process, it is a combination of temperature and fluid velocity that dictate the efficiency with which the frozen contaminants are dislodged from the aircraft's surfaces. This is most effectively accomplished with a nozzle spray angle of approximately 45 degrees. Contaminants not removed from the surfaces by the initial impact of the fluid are melted off, or debonded, by virtue of the thermal energy contained in the heated deicing fluid.
Excess pressure can result in fluid velocities out of the nozzle that can cause impact damage to aircraft components. The aircraft manufacturer should be consulted to ensure that any proposed deicing procedures will not damage the aircraft and render it unsafe for flight.
When applying anti-icing (AAF) fluids to the aircraft surfaces only correct pumping equipment must be used to avoid shearing the fluid and thereby destroying the fluid's HOT capacity. The fluid manufacturer should be contacted to determine what methods should be employed in the application of their fluids.
10.6.2 Proper Coverage
Proper fluid coverage is absolutely essential for proper fluid performance. It is imperative that the personnel applying the fluid are properly trained and that a consistent fluid application technique is utilized. Adequate fluid quantities must be expended to accomplish the de/anti-icing tasks. Proper training will help ensure that the de/anti-icing task is accomplished in a manner that utilizes the fluids most effectively and that the aircraft is subsequently rendered safe for flight.
The deicing with fluids process is not completed until the aircraft's critical surfaces are completely free from frozen contamination. This can only be accomplished with the use of a sufficient quantity of deicing fluid to complete the task.
For the purpose of deicing, hot TypeI fluid is generally applied directly onto the total aircraft surface to be de-iced. If applied only to the front part of the wing, allowing it to flow back to the aft part, the fluid will cool down significantly as it moves on the surface of the wing making it less effective, or even ineffective in melting frozen contamination on the aft part of the wing.
It is considered imperative that the leading edges of the wings and control surfaces be thoroughly cleaned of any contaminant. No frozen precipitation or contamination can be allowed to remain underneath the deicing fluid. Hot TypeI fluid must be applied in sufficient quantity that the remaining fluid on the surfaces to be protected has a freezing point at least 10°C below Outside Air Temperature (OAT). As the fluid is applied, it is being diluted by the melted ice, snow or whatever frozen accumulation it is removing. Its freezing point is thus increased.
Sufficient hot deicing fluid must be applied to make sure that fluid diluted by melted slush, snow or ice is flushed away. This is best accomplished by applying the fluid from the high point on the wing to the low point on the wing. Typically from wing tip to wing root.
The anti-icing process is not properly accomplished if an insufficient amount fluid has been used and which results in incomplete or inadequate coverage of the surfaces to be treated.
For the second step of a two step procedure, a sufficient amount of aircraft anti-icing fluid must be applied that can completely cover the surfaces and form an adequate coating. The HOT table values are based upon the application of sufficient fluid. Insufficient coverage results in a thin layer and reduced protection of uncertain duration.
The application process should be continuous and as short as possible. Anti-icing should be carried out as near to the departure time as possible in order to utilize available holdover time. While thickness will vary in time over the profile of the wing surface, the anti-icing fluid should be distributed uniformly. In order to control the uniformity, all horizontal aircraft surfaces should be visually checked during application of the fluid. The amount of fluid required, will be visually indicated by the fluid just beginning to run off the leading and trailing edges of the surfaces.
For a typical ethylene based TypeIV fluid, between 1 mm and 3 mm thickness layer is required. It takes 2 litres of fluid to cover 1 square metre to a depth of 2 mm. Since application is never perfect, it will take more than 2 litres/square metres to achieve this 2 mm fluid thickness (In non-metric units, it will take at least 2 U.S. gallon/40sq. ft. to achieve 0.08inches). Conversion factors:
- 2 litre = 0.5284 U.S. gallon;
- 2 mm = about 0.08 inch; and
- 1 square metre = 10.76 square feet.
NOTE: For more detailed information on specific fluids, contact the de/anti-icing fluid manufacturer.
10.6.2.3 HEAT LOSS
The heated ADF should be dispensed, as close to the surface to be deiced as possible, however a solid flow of fluid should not be pointed directly at the surface. The fluid should be applied at a low angle to avoid damage to the aircraft surfaces. Application of heated fluid from a distance results in the significant cooling of the fluid enroute to the aircraft surfaces, which will reduce the fluid's ability to remove frozen contaminants. The thermal energy contained in heated ADF fluids has been shown to be a principle factor in the efficient removal of frozen contaminants from the aircraft's surfaces. Therefore, within limits, the hotter the fluid is when it reaches the aircraft's surfaces, the more effective it will be in removing the contaminants. The deicing operator training program will need to emphasize correct techniques to get the best performance from the fluid in use.
10.6.2.4 AREAS TO BE COVERED
The application strategy should adopt standard techniques while considering unique procedures necessary for specific aircraft design differences. Where possible, mechanical removal of snow, ice or slush accumulations should be considered as well as the proper execution of such procedures.
All windows and doors of the aircraft must be closed during spraying. The engine may be shut down or idling and air-conditioning and/or APU air must be off, unless otherwise recommended by the airframe and engine manufacturer.
A spray to provide an even and uniformly distributed film should be used in a continuous process of application.
The surfaces to be treated are typically:
- Wing leading and trailing edges;
- Wing and controls upper surfaces;
- Horizontal stabilizer and elevator upper surfaces;
- Vertical stabilizer and rudder; and
- Fuselage upper surfaces on aircraft with rear fuselage mounted engines, depending on amount and type of precipitation. Follow the aircraft manufacturers' recommendations with respect to anti-icing the fuselage of aircraft with rear mounted engines.
Care must be taken to ensure that ice, snow and slush has not accumulated or has not been overlooked in critical places such as the flight control hinge areas, auxiliary power unit (APU) intake or between stationary and moveable surfaces. The front and rear sides of fan blades must be checked prior to start-up when engines are not running. Clear ice can form below a layer of snow or slush and can be hard to detect therefore the surface of the aircraft must be carefully examined after deicing. Care must be taken to avoid inadvertently spraying fluid directly onto the cabin and cockpit windows, doors and emergency exits, or into the APU intake whether running or not.
In general, deicing treatment must be done in a leading edge to trailing edge direction. Failure to follow this methodology may result in contamination being forced into the wing or stabilizer openings where it could re-freeze and jam control systems and thereby result in an unsafe condition.
NOTE: T-tail aircraft have the potential to tip due to the imbalance caused when the wings are clean and the tail surfaces have heavy accumulation. The tail should be de-iced first when heavy contamination is present.
10.6.3 Excessive application
Excess application can become a safety problem. The tarmac surfaces become slippery because of the fluid and the clean up process become onerous and expensive. Any accumulation of fluid on the ground must be cleaned up and disposed of in a safe and environmentally friendly manner.
Training of deicing crews will help minimize waste and deicing costs.
10.7 Fluid Dry Out
There have been reported incidents of restricted movement of flight control surfaces, while in flight, which has been attributed to fluid dry out. Further, testing has shown that diluted TypeII and IV fluids can produce more of a gel residue than neat (i.e.: undiluted) fluids.
Dry out may occur with repeated use of TypeII and IV fluids without prior application of hot water or without a heated TypeI fluid mixture. The result can be that fluid will collect in aerodynamically quiet areas or crevices. The fluids do not flow out of these areas during normal take off conditions. These residues have been known to re-hydrate and expand under certain atmospheric conditions, such as during high humidity or rain. Subsequent to re-hydration the residues may freeze, typically during flight at higher altitudes. The re-hydrated fluid gels have been found in and around gaps between stabilizers, elevators, tabs, and hinge areas. The problem can be exacerbated for aircraft without powered controls. Pilots have reported that they have had to reduce their altitude until the frozen residue melted, which restored full flight control movement.
A number of European Air Operators have reported this condition when they have used a diluted TypeII or IV fluid as a first step and then a concentrated TypeII or IV as a second step in their de/anti-icing process. North American Air Operators, to date, have not reported this situation. It is considered likely that because the North American Operators typically use a heated TypeI fluid followed by either a TypeII or IV fluid there has not been an occurrence of fluid dry out in North American operations.
It is suggested that regular spraying of aircraft with a hot TypeI fluid/water mixture may alleviate the occurrence of fluid dry out. Such routine procedures may result in the requirement for more frequent lubrication of components. If the high-pressure washing does not clear the gel, it may be necessary to implement maintenance procedures to address the issue. An increased frequency of inspection is recommended, to help avoid difficulties in flight due to a fluid dry out condition. Special attention should be paid to inspection of such areas as: spaces in the area of flight controls; between the horizontal stabilizer and the elevator; spaces between the flaps and the wing, including any associated drain holes in these areas; and other such areas where fluid may collect.
There is some concern that the recently introduced TypeIII fluids may also be susceptible to dry out. Given their recent introduction there is very little experience to draw on, therefore it is recommended that anyone intending to use TypeIII fluids contact the fluid manufacturer for further information on fluid dry out and establish a program to monitor for TypeIII fluid dry out.
10.8 Deicing and Anti-icing Fluid Compatibility
Research has indicated that the effectiveness of a TypeIV fluid can be seriously diminished if proper procedures are not followed when applying it over a TypeI fluid, specifically, a sufficient quantity of TypeIV fluid should be applied to displace any remaining TypeI fluid from the aircraft surfaces.
Operators should ensure that the TypeI and TypeIV fluids being used on their aircraft are compatible. This can be accomplished by contacting the respective fluid manufacturer.
10.9 Blending Type I Fluids
For economic and environmental reasons Fluid Blending has become a viable option at some Canadian Airports. ADF Concentrate can be blended dependent upon the outside air temperature and the type of deicing process that will be accomplished (i.e. one step or two step process).
Irrespective of the glycol/water mixture ratio, all TypeI fluids will be referred to as "TypeI" fluids, provided that the fluid freezing point exceeds the required Lowest Operational Use Temperature (LOUT) value.
TypeI fluid may be diluted and used to deice aircraft in accordance with the fluid concentration and temperature charts provided by the fluid manufacturer.
10.10 Using TypeIV Fluid to Prevent Frost Formation Overnight
There are occasions when air operators apply TypeIV fluid to the critical surfaces of an aircraft in the evening prior to the period of the day when frost will start to form. The holdover time for TypeIV fluid during active frost conditions is longer than other precipitation conditions. A determination on what subsequent de/anti-icing operations are required will depend on: the type of precipitation experienced by the aircraft, whether the HOT has expired, and the results of an inspection to confirm that the integrity of the fluid has been maintained and that contamination is not adhering to the critical surfaces.
NOTE: Dehydration of the fluid can negatively impact the fluid performance.
Should precipitation start, in general, there will be a requirement to completely deice and then anti-ice the aircraft to establish a valid HOT.
There are a large number of ground icing operational situations for which there isn't an exact procedure and which will require sound operational judgment.
The Air Operator should always contact the fluid manufacturer for guidance on the use of their fluid.
NOTE: The operator shall inspect the critical surfaces to ensure that the fluid integrity has been maintained (e.g.: fluid has not jelled). Check with the fluid manufacturer to determine what procedure to follow if a jell has formed.
10.11 Applying TypeIV Fluid in a Hangar
There are operational conditions when Air Operators may chose to anti-ice their aircraft while the aircraft remains in a heated hangar. This is one way in which to reduce the consumption of deicing fluid and to reduce the environmental impact of deicing.
The period of time after TypeIV fluid application, and the air temperature in the hangar both have an effect on the ability of the fluid to protect the aircraft when it is pulled out of the hangar and into the frozen precipitation. The HOT available from a fluid is based largely upon the fluid's thickness on the surface. The fluid thickness varies with time and temperature.
The air operator is advised to consult with the fluid manufacturer for guidance on using their fluids under these conditions. A minimum of a fluid thickness measurement may be required, dependent upon the circumstances, to ensure that the predicted fluid HOT protection is available.
10.12 Manual Methods
Reducing the amount of deicing fluid used can have a positive impact on both the cost and the environmental. Manual methods of snow removal should be used whenever possible, as long as safety is not compromised. There are a wide variety of devices available to assist in the removal of frozen contaminants from aircraft. Factors such as temperature, amount of contamination, wind conditions, and contaminant location must be taken into account when choosing the method.
Under extremely low temperatures, the use of glycol based fluids is limited (refer to the fluid manufacturers' specifications for details). In these circumstances, manual methods may be the only option.
Some of the more common devices are:
NOTE: Extreme care must be taken anytime manual methods are used to protect the highly sensitive and often fragile sensors and navigation antennas. Also very vulnerable to damage are: pitot tubes, static ports, angle of attack sensors, and vortex generators. When sweeping or "pulling" contamination off an aircraft, care must be taken to use motions which pull contamination away from any openings, in order to avoid forcing the contamination into any openings on the wings or stabilizers.
The most commonly used and most readily available manual tool is the broom. Although a common household broom could be used, a larger, sturdier commercial variety is usually chosen. Care must be taken to ensure the bristles are sturdy enough to be effective, yet not so stiff as to do damage to the skin of the aircraft. The broom that is to be used to sweep the snow should not be used to break the ice or to sweep floors and other surfaces.
Brooms are very useful in cleaning windows and other sensitive areas (e.g.: a radome) where the application of hot liquid is best avoided or prohibited.
Extra attention should be paid to safety, especially when combined with the tendency to stretch the reach with a broom. If a ladder or other such device is used, personnel must be certain that it is safe to use. Slippery surfaces can make climbing dangerous.
Personnel have attempted to sweep snow from wing and tail surfaces while standing on these surfaces. This is an extremely unsafe practice with a very high risk of a slip and fall accident. As well, many surfaces are not stressed to support the weight of a person.
Using the wing broom to remove contamination does always mean that the wing surface is clean and safe for flight. Every time a broom is used to remove contamination a tactile inspection shall be done. If any contamination is found adhering to a critical surface, it shall be removed prior to flight.
The following points should be considered when using a broom to clean frozen contaminants from the critical surfaces of an aircraft:
- Ensure the flight crew and/or maintenance personnel conducting aircraft checks are aware that contamination removal is being conducted and advise them when the removal procedures are complete;
- Ensure that control surfaces are in the "neutral" position (all leading edge devices, flaps and spoilers are retracted, unless they are deployed for an operational reason);
- Ensure the horizontal stabilizer is in the full nose down position;
- For safety reasons, sweep from the bucket of a deicing vehicle or use the wing inspection ladder;
- Sweep from leading edge of the wing to the tailing edge. Generally try not to push contamination from the trailing edge towards the leading edge, otherwise this may push frozen contamination into cracks and crevasses and cause flight control difficulties later;
- Generally, sweep contamination from wing tip to wing root;
- Sweep contamination away from flight controls, hinges points and bay areas; and
- If all of the contamination cannot be removed when working from the leading edge, because the broom is not long enough, then remove the remaining contamination by dragging it off the trailing edge. Ensure that the handle of the broom does not come in contact with the wing flap or any other surface of the wing because damage may result.
Ropes have also been used effectively to "pull" heavy snow off a wing. Care must be taken when the rope is getting close to the actual skin of the aircraft. Ropes are much less effective on light "fluffy" snow. The ropes are typically used in a seesaw motion between two persons, with the rope touching the aircraft's surface.
Rope can be used in an effort to remove accumulations of frost, typically from high wing and tail surfaces. Care must be taken to avoid damage to the finish of the paint or to the deicing boot.
A thorough inspection must be accomplished to ensure that the critical surfaces are clean for take off. It may be necessary to follow up with another method to get the critical surfaces completely clean.
The most common type of scraper used is the commercial variety used to remove accumulation from building roofs. Because the handles of this type of scraper will often make contact with the wing, care must be taken to protect the wing. This can be accomplished by covering the handle with a foam wrap. Normally best with wet heavy snow, the scraper should be used in a pulling motion from Leading Edge to Trailing edge (i.e.: lay the scraper high on the aircraft surface and pull toward you).
Also available commercially, and of similar benefit to the scraper, is the squeegee. Squeegees are generally available in a variety of sizes and have foam or a similarly soft material on one side and a rubber blade on the other side.
10.12.4 Polishing frost
Polishing frost is not considered an acceptable method of preparing an aircraft for flight. This method would leave frost contamination on the critical surfaces prior to take off, which would not comply with Regulation CAR602.11 and GOFR Standard CASS622.11, and would not satisfy the "clean wing concept".
10.12.5 Portable Forced Air Heaters
Heat from a portable forced air heater can effectively remove frost and ice from critical surfaces. These heaters are commonly found in remote and Northern Canadian locations and are normally used to heat aircraft interiors and to pre-heat aircraft engines.
The operator directs the airflow from a flexible duct onto the contaminated surface and the combined effect of the heated air and low velocity airflow melts and evaporates contaminants.
Special precautions may be required when using this method because the water resulting from melting the frozen contaminants may flow into flight control or other sensitive spaces and later re-freeze. The consequences may be that the controls won't function properly.
This technique has the effect of briefly warming the wing surface and can cause snow or other contaminants to stick to the surface when precipitation is present. The operator must keep moving the duct to avoid overheating any spot as these heaters generate enough heat to cause damage to de-ice boots and other equipment if directed at a single spot for too long.
10.13 Technology Options
10.13.1 Alternate Technologies
The cost and potential environmental impact of deicing with conventional fluids, has driven the demand for the development of alternate deicing technologies. When considering the benefits of these technologies, it is important to understand that while the methodology may differ from that used with conventional fluids, the basic principles of de/anti-icing still apply. Some of the alternate technologies, available at the time of publication, are described in this section.
10.13.2 Infrared Heat Systems
Transport Canada approval for operational use of these systems at airports and on commercial aeroplanes had not been undertaken at the time of publication.
10.13.3 Hot Water
Hot water can be used to remove large amounts of contamination (such as ice) from an aircraft provided that the Outside Air Temperature is above 0°C as per the Transport Canada guideline. All surfaces sprayed with water must be over-sprayed immediately with full strength heated Type I fluid to prevent the water from freezing.
Deicing with hot water requires many safety precautions and separate equipment. Following is guidance for deicing using hot water:
- Ensure personnel are trained in procedures for hot water deicing;
- Ensure that an appropriate and serviceable deicing vehicle is on site;
- Ensure that the truck tanks are identified by placarding each tank; e.g., water/100% glycol;
- Prior to using a vehicle for a deicing operation, verify the contents of each tank and perform a refractometer test on the contents;
- Ensure that the water temperature is between 140-180°F (60-82°C);
- Ensure that the ambient temperatures are reviewed hourly and compared to the permitted temperature ranges for water usage; and
- Immediately over-spray all surfaces sprayed with water using heated TypeI fluid. TypeIV should NOT be applied after applying hot water unless an application of heated TypeI is applied first.
10.13.4 Forced Air Systems
The use of forced air to remove contaminants, particularly snow, is a maturing technology. The concerns regarding the effect of large quantities of deicing fluid on the environment, in particular, has resulted in renewed forced air research efforts in recent years.
The results of the research are promising but as with any technology, there are compromises to be made when using forced air systems. Nonetheless, ongoing research is revealing that there is significant potential for forced air systems both in terms of economic savings and environmental relief.
A subsequent inspection of the critical surfaces will be required after the use of Forced Air.
The use of Forced Air is subject to approval from aircraft manufacturer.
10.13.4.2 GENERAL GUIDANCE ON THE USE OF FORCED AIR
The use of forced air to remove contamination from aircraft surfaces may save time and money. Forced air can be used as a one-step or a two-step process.
If using as a one-step procedure to remove contamination, the operator shall verify by a tactile inspection that the surface is clean and clear of contamination. If forced air has not removed all the contamination from the surfaces or you are not sure all contamination is remove, then an application of heated TypeI is required.
Below are some suggested procedures when using forced air to remove contamination:
- Ensure that the flight crew and/or maintenance personnel conducting aircraft checks are aware that contamination removal is being conducted and when the removal procedures are complete;
- Ensure that ground-handling staff is not loading/unloading baggage when forced air is being used;
- Ensure that all cabin doors and cockpit windows are closed;
- Ensure that the forced air is approximately the same temperature as the OAT. If air is hotter than OAT, this may melt the contamination causing it to re-freeze on the aircraft surface;
- Always check with the aircraft manufacturer prior to using forced air on structures made of honeycomb;
- Blow contamination from leading edge to trailing edge of the wings and stabilizers. Generally, don't use forced air to blow contamination from trailing edge to leading edge because this could force contaminants into the balance bays and into other cavities;
- Avoid using the forced near windscreen wipers, because damage may result;
- Avoid using the forced air in areas that are made of rubber, plastic or other soft material, as damage may result;
- The tip of the forced air nozzle should be no closer than three feet from the contaminated surface.
10.13.4.3 FORCED AIR MODES
Forced Air alone
The use of forced air alone to remove contaminants is reasonably efficient when used to remove loose snow, but requires more diligence when used to remove adhering contaminants.
The effectiveness of forced air, at removing contaminants from the critical surfaces, depends upon a number of factors including: air stream velocity, air stream temperature, operator training and experience, outside air temperature, weather conditions and others.
Forced Air augmented with TypeI fluid
Heated TypeI fluid is injected into the high speed air stream.
One advantage of this deicing method compared to the air alone system is that heated TypeI fluid carries more thermal energy than just air alone. Heat is the principal mechanism for removing adhering contaminants from an aircraft's critical surfaces; hence the ability to remove contaminants is enhanced with this method.
Forced air with Type II and/or Type IV fluids injected in the air stream, or applied over the air stream
The combination of anti-icing fluid and high speed forced air introduces some new concerns as well as some benefits.
The anti-icing fluids must be handled correctly in order to retain their viscosity characteristics. One of the effects of injecting TypeII & IV fluids into a high speed air stream is that of shear. If these fluids are sheared significantly they lose some of their viscosity.
The significance of this shear concern is that if the fluids are sheared excessively, the HOT values will not be valid for the fluid.
Excessive foaming is also a significant issue.
It is anticipated that the concern about loss of viscosity will be addressed as forced air system design and operation are advanced.
10.13.4.4 SAFETY ISSUES
The high speed airflow present in forced air systems can cause serious injury. Proper training and the use of protective equipment are required.
The noise level of forced air systems is typically very high. Hearing protection is a necessity when operating or working near these systems.
The high velocity air stream removes frozen contaminants from the aircraft and propels them at high speed. Personnel near a deicing operation, which is using a forced air system must be alerted to the fact that high speed debris is present.
Aircraft may be damaged by frozen projectiles. Care must be taken to direct the ice away from the aircraft surfaces, which may be struck with considerable force. Aft mounted engines are particularly vulnerable to ice FOD from this process. Aft mounted engines should always be shut down when deicing with force air.
10.13.4.5 EVALUATION FOR OPERATIONAL USE
Transport Canada has not evaluated a forced air system for operational use, at the time of publication of this document.
Transport Canada, Commercial and Business Aviation Branch, Operational Standards Division (AARXB), should be contacted to discuss any proposal to use these systems during Commercial aircraft ground icing operations.
10.13.5 Ground Ice Detection Systems (GIDS)
The development of ground ice detection sensor technologies has been stimulated by the difficulty in determining if an aircraft is free of frozen contaminants prior to take off. The human has a limited ability to accurately evaluate the condition of an aircraft's critical surface during ground icing operations. The limitations include: poor lighting conditions, visibility restrictions due to blowing snow, the difficulty in determining whether or not clear ice is present, and others. The advanced technologies used in GIDS may be able to overcome some of the human limitations.
For the purposes of this document these sensors, as a group, are referred to as Ground Ice Detection Systems (GIDS). A design standard for these systems is identified in SAE document AS5116.
This SAE Aerospace Standard AS5116, Minimum Operational Performance Specification (MOPS), specifies the minimum performance requirements of Ground Ice Detection Systems (GIDS). These systems may be mounted onboard the airplane, or be ground-based. They may provide information for indication and/or control.
10.13.5.1 FUNCTIONAL DESCRIPTION OF GIDS (EXTRACTED FROM SAE AS 5116)
GIDS are intended to be used during airplane ground operations to inform the ground crew and/or the flight crew and/or a relevant system about the condition of monitored airplane surfaces.The GIDS function is:
- Frozen contamination detection; and/or
- Fluid contamination monitoring.
10.13.5.2 GIDS TYPES
- Airplane mounted systems are designated as Onboard GIDS.
- Ground-based, hand held, pedestal or truck mounted systems are designated as Ground-based GIDS.
10.13.5.3 GIDS DESIGN
GIDS are designed to detect the presence of frost, ice, slush, or snow on the surface where the sensor makes its measurement. They are designed to be capable of detecting the presence of a frozen contaminant of a specified thickness under operational weather conditions.
GIDS should be capable of providing accurate and reliable indications of aircraft critical surface contamination for all of the operational conditions in which they will be employed.
Generally there are two broad categories of sensors, and they are:
- Wide area sensors; and
- Spot sensors.
10.13.5.4 OPERATIONAL APPROVAL AND USE
The operational approval for GIDS use in Canada remains under investigation by Transport Canada, Commercial and Business Aviation Branch (AARX), as of April 2005. There are many concerns to be addressed prior incorporating an electronic device into an Air Operator's ground icing program to replace the human for the purpose of detecting the presence of frozen contaminants on an aircraft's critical surfaces.
10.13.6 Engines Running Deicing
Deicing crews must receive specific training to support "engines on" operations. Training subjects should include, but are not limited to:
- The potential effects of jet blast;
- Safety zones around running engines;
- Fluid application techniques - differences may exist;
- Effective positioning of deicing vehicles (including specific vehicle travel patterns);
- Do not spray fluids into aircraft engines, and why;
- Considerations for wing mounted engines vs. rear mounted or tail mounted engines;
- Engine inlet inspections; and
- Pilot communication requirements.
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