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In flights, ice is bad news because it destroys the flow of air, increase drug and decrease the ability of an airfoil to create lift. Normally, ice accumulates on the exposed frontal parts of an aircraft as well as on antennas, propellers, windshield, intakes, vents, wings and cowlings. In some cases, an aircraft can be iced to an extent that continued flight becomes impossible. Due to icing, an aircraft may roll uncontrollably and recovery might not be achieved. Also, ice may make the engine to stop by blocking the air source or icing up the carburetor (AOPA). To avoid these problems, deicing is necessary. Aircraft de-icing is a process of removing ice from the surface of an aircraft. This paper gives the history of deicing on aircraft, describes various deicing equipments the methods of deicing as well as their effectiveness.
History of Deicing on Aircraft
In the early years of commercial air travel, the decision to deice a plane was made by the captain or the airline. Throughout the industry, there was a tendency to resist deicing as much as possible because of time constraints, low operating budgets, and a general lack of knowledge about the perils of ice on aircraft. Use of technology was limited, particularly for smaller companies whose aircrafts did not have amenities such as the heated windshields. In one case, a pilot was equipped with a car windshield scraper to scrape the ice off the aircraft’s windscreen from a side window while on approach. Although it was technically illegal for an aircraft to take off with ice-contaminated wings, a gray area existed because the decision was generally left to discretion of the captain. For example, if a light snow was falling, some pilots would elect not to deice thinking that the snow would blow off. In most cases, it probably would, but as it can be attested by history books, exceptions always exist. Nowadays, any second-guessing is totally removed from the equation. The American regulations now prohibit takeoff when ice is adhering to any critical surface of an aircraft, including the lifting and control surfaces, tail and wings, and upper fuselage surfaces on aircraft with rear-mounted engines. This rule is referred to as “clean aircraft concept.” (Morris, 2007).
The main exception to the new regulations allows a coating of frost up to one-eighth of an inch thick on lower wing surfaces in areas cold-soaked by fuel, between the forward and after spars. Deicing also is not mandatory if the captain expects dry snow lying on top of a cold, dry, and otherwise clean wing to blow off during takeoff. For aircraft types where the upper fuselage is a critical surface, a thin coating of frost is permitted in the area provided the deposit is thin enough that underlying surface fixtures such as the markings, paint lines and letterings can be distinguished. Although the pilots are in charge of deciding whether deciding is required, the “lead” ramp attendant can overrule the decision not to deice. Even flight attendants and passengers can voice concerns about the aircraft’s deicing efforts, although the final decision rests with the pilot (Morris, 2007).
Methods of Deicing and Their Effectiveness
- Hot Water Aircraft Deicing
The FAA permits aircraft to be deiced using hot water followed by the application of an anti-icing fluid when ambient air temperatures are above 270F. None of the major U.S. airlines currently use this method because they believe it would compromise the safety of passengers and ground operations staff. Airlines are concerned about flash freezing and the potential to build up thick of ice both on the pavement and on the aircraft. The water may also enter and freeze on flap tracks, elevators, and other airplane parts, potentially affecting aircraft handling and performance. Water freezing in hoses, nozzles, and tanks when the deicer trucks are not in use is also a major concern.
- Enclosed- Basket Deicing Trucks
Typically, airlines use open air-basket configurations referred to as “cherry pickers” to apply ADF. The open baskets provide little protection for personnel, who are frequently sprayed by the aircraft deicing and anti-icing fluids. An enclosed-basket design is now available that improves the operator working conditions. By enabling operators to get closer to the aircraft, the enclosed basket repeatedly reduces over-spray and helps to minimize the volume of fluid used to deice aircraft. As a result, some airlines have reported thirty percent reductions in aircraft deicing fluid usage. As a result of these benefits, many airlines in the United States now employ a fleet enclosed-basket deicing trucks at their hubs and larger stations. Several companies manufacture the air-basket deicing trucks (United States. Environmental Protection Agency. Office of Water).
- Mechanical Methods
The volume of ADF applied to aircraft can be minimized by mechanically deicing the aircraft the aircraft prior to chemical deicing. For example, the U.S Air Force uses booms, squeegees and ropes to remove ice and snow from the surfaces of aircrafts. These methods are more effective at removing snow rather than ice. When performed incorrectly, these methods can damage the aircraft’s sensors and antennas. Mechanical methods are generally only practical for smaller aircraft; for large aircraft, they can be prohibitively time consuming as well as labor intensive. Despite these disadvantages, the Northwest Airlines uses brooms which are fitted with long handles to remove snow from large passenger aircraft. This method is used only in the early mornings, when it is least disruptive to departure schedule. At several U.S Air Forces bases, aircraft parked on ramps are oriented to maximize the melting of accumulated snow and ice by sunlight. This method reduces the volume of aircraft deicing fluid used during winter season, but it is practical only for general aviation and certain military flights that can be delayed without operational and economic impacts (United States. Environmental Protection Agency. Office of Water).
- Hangar storage method
Many general aircraft and some commuter aircraft are stored in hangers overnight and during storm events, eliminating the need for aircraft deicing. In addition, heated aircraft hangars are sometimes used in deicing of aircraft. In either case, anti-icing may be necessary in certain weather conditions to prevent ice and snow from accumulating on the surfaces of aircraft during taxiing and takeoff. After leaving the hangar, aircraft are anti-iced by spraying with a small volume of glycol-based anti-iced fluid. Because of the small volumes applied, the volume of ADF-contaminated wastewater generated is much less than would have been stored outdoors (United States. Environmental Protection Agency. Office of Water).
- Aircraft Covers
Where hangar space is unavailable, aircraft covers or blankets are sometimes used as an alternative method of minimizing ice and snow accumulation on aircraft surfaces. Aircraft covers are typically used for small general aviation aircraft to protect the tail, wing and engine inlets. There are currently two types of covers that are available: mesh and solid covers. Mesh covers are made of a very fine mesh fabric and are designed for use in windy conditions. They are easier to remove in cold weather but provide less protection, tending to leave residual ice on the surfaces of the wings. Solid covers are made from nylon or canvas and should not be used in strong winds. In cold weather, the soli covers tend to become hard and freeze to wings, making them very difficult to remove. For example, the Northwest Airlines experimented with aircraft covers for large passenger aircraft, but was dissatisfied with their performance. Northwest found them to be relatively easy to install, but difficult and time-consuming to remove as they become hard and inflexible when cold. In some instances, condensation trapped between the wing and cover front froze, binding the cover tightly to the wing surface. In addition, covers that came in contact with the pavement picked up grit, which damaged aircraft surfaces as the cover was pulled into place (United States. Environmental Protection Agency. Office of Water).
Aircraft Deicing Equipments
Typically, trucks or fixed booms are used to apply ADF. Some deicer trucks contain multiple storage compartments to carry deicing fluids of varying types and strengths. Storage tanks are equipped with thermal blankets to heat the fluids. The deicing trucks have a movable boom with a cherry picker equipped with a nozzle at the end of the boom. An operator in the cherry picker basket directs the high pressure spry at aircraft surfaces while the truck is moved by a driver. Specially designed deicing trucks may be used to deice areas of the aircraft that are low to the ground or hard to reach. Airports are equipped with fixed-boom deicing equipments, which typically include a permanently mounted boom with a nozzle, or a cherry picker with a nozzle, that moves along the boom. Pumps supply ADF from mixing tanks to the boom. Because fixed booms are less mobile than deicing truck, deicing trucks may be needed to deice hard-to reach areas. Aircraft deicing operations usually occur at terminal gates, gate aprons, taxiways, or pads. Aircraft deicing pads are located near terminal and gates (EPA).
There are also Computer-Controlled Fixed-Gantry Aircraft Systems. These systems have only been installed in few airports in the world. In the typical gantry system, an aircraft taxi into the gantry where the nozzles mounted on the gantry frame spay it with a hot deicing fluid. These nozzles are controlled by computers that are programmed to deliver the appropriate amount of fluid uniformly over the entire aircraft for a variety of types and sizes. The gantry systems are typically located on taxiways near the end of the principal departure runway. In addition, we have Infrared Aircraft Deicing Technology equipment which relies on infrared radiation for deicing.
Finally, there are Forced-Air Aircraft Deicing Systems which have been used for many years but have not seen much application in the United States due to their high cost over other systems. The first system used a high pressure air jet to blast ice and snow from aircraft surfaces, which has proven to be very effective for removing dry, powdery snow form aircraft surfaces. For example, All Nippon Airways Has used forced air systems for many years to remove overnight accumulations of snow at several northern airports in Japan. In the past, United States carriers were less enthusiastic about forced air systems because they were not very effective for removing ice and wet snow; conditions that are typical for most united states airports. In 1990s, a forced system deicing system was developed to remove snow and ice from aircraft surfaces using high pressure air stream combined with a fine spray of glycol-based aircraft fluid. The system consists of a self contained, truck-mounted unit fitted with a turbine engine and a dual source nozzle which allows deicing fluid to be added to the air stream to help in removing ice (EPA).
In fact, aircraft deicing process is a very vital part in aircraft and passenger safety as well as in airport management. Because of this, it makes sense for all airports to invest and change their deicing systems as well as procedures to accommodate new technology. This will ensure safety and less capital expenditure.