Association of European Airlines (AEA) defines Deicing as a procedure by which frost, ice, slush, or snow is removed from an aircraft to provide clean surfaces. Often, deicing is misunderstood to be the same as Anti-icing, which is a preventive procedure to protect against the formation of frost or ice and accumulation of snow or slush on treated surfaces of the aircraft for a limited period (holdover time).
The Federal Aviation Administration (FAA) requires aircraft surfaces to be deiced and anti iced to ensure the safety of passengers. There are two basic types of deicing/anti-icing operations carried out at airports: the deicing/anti-icing of aircraft and the deicing/anti-icing of paved areas, including runways, taxiways, and gate areas.
As defined, deicing follows a stepwise procedure to remove Ice, snow, slush, or frost from aircraft surfaces by heated fluids, mechanical methods, alternate technologies, or combinations. Basically, deicing is based on the principle that heat in a fluid effectively melts any frost and light deposits of snow, slush, and ice. Heavier accumulations require heat to break the bond between the frozen deposits and the structure; the hydraulic force of the fluid spray is then forced to flush off the residue.
The following is the standard procedure laid out by AEA and accepted as an international standard for deicing using fluids.
Stage 1: Preparing the surface or Pre-step process: Upon mutual consent with the aircraft operator, a pre-step process before the de-icing process can be carried out to remove large amounts of frozen contamination (e.g., snow, slush, or ice). The pre-step process may be performed with several methods, such as using brooms, forced air, heat, heated water, and heated fluids with a negative buffer freezing point. The pre-step process can help in reducing the quantity of glycol-based de-icing fluid required during the main de-icing process..
Stage 2: Removal of frost and light ice: A nozzle setting giving a solid cone (fan) spray should be used to ensure the largest droplet patter and retain the maximum heat in the fluid.
Stage 3: Removal of snow: A nozzle setting sufficient to flush off deposits and minimize foam production is recommended. Heavier deposits often require heavier fluid flow to remove snow from the aircraft surfaces. For light deposits (both wet and dry snow), similar procedures as for frost removal may be adopted.
Stage 4: Removal of ice: Heated fluid shall be used to break the ice bond. The method makes use of the high thermal conductivity of the metal skin. A stream of hot liquid is directed at close range onto one spot at an angle of less than 90° until the aircraft’s skin is just exposed.
Note: By applying the heated fluid close to the aircraft skin, a minimal amount of fluid will be required to melt the deposit and save operational costs.
Aircraft deicing trucks are mounted with a crane-lifted basket, wherein the operator sits in the basket and controls the deicing fluid sprayer. Trucks typically consist of up to 30,000-gallon glycol tanks with propylene glycol and water mixture for deicing. The tank is connected to the hose and nozzle system to spray glycol onto the aircraft surface. Deicing trucks are powered by Internal Combustion Diesel Engines, which provide rotational power to pumps to spray glycol through nozzles up to 200 LPM, varying flow.
Deicer Boom trucks consist of a rotating telescopic-boom crane mounted on the truck chassis. This configuration allows for ease of lifting equipment transporting to job sites and allows the boom truck to maximize utilization during a deicing process. Boom tests are usually performed to test the strength of the crane and lift ability. New York state code rule 23-8 lays out procedures for testing Mobile Cranes, Towers, and Derricks.
The AEA has laid out standard De-icing/anti-icing procedures, which sternly mention that the operations be carried out exclusively by personnel trained and qualified on this subject. Companies providing de-icing/anti-icing services should have both a Qualification Programme and a Quality Assurance Programme to monitor and maintain an acceptable level of competence.
FAA Considers the Deicing program as critical ground support equipment, and hence proper maintenance and inspection are vital. Following are the inspection and PM guidelines are laid out by the DEPARTMENT OF THE AIR FORCE, Headquarters US Air Force, Washington, D.C. 20330-1030.
A Deicer Truck PM plan should also include load bank and boom testing to check the engine’s performance and boom load-carrying capacity. These tests simulate the high load on the engine and the cranes as a part of preventive maintenance activity.
Aircraft operators should assimilate that a Deicer vehicle is not just a truck. Every time while performing a deicing operation, glycol is sprayed onto the expensive Aerofoil design, and there is a potential risk of damaging the aircraft components. Therefore, it is essential to deliver clean, carefully regulated glycol while performing deicing operations. An accidental or unregulated flow could destroy sensitive and expensive aircraft electronic and avionics systems.
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