Cold and ice are a major problem in airports of the cold countries – especially in places like Ottawa. The first thing for the team is to understand the twin problems of de-icing and anti-icing, how they can be addressed, and lastly the gravity of the task and the serious dangers involved if the work is not done properly. Put simply de-icing is the removal of the ice and frost that already adheres to the framework of the aircraft and anti-icing is the taking of preventive measures to see that ice does not form from the time of de-icing to the taking off the moment when the plane is airborne. This is done with the help of some special de-icing and anti-icing fluids.
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Ice that forms on the framework of the aircraft and its engines or air inlets needs to be removed. This is de-icing. Anti-icing is steps taken to prevent the further formation of these conditions. Water freezes at 0°C. If the temperatures near the plane drop below this, ice forms from drops of water as soon as it comes in contact with the plane. The icing on the frame reduces the performance, causes loss of lift, alters controls, and in the end stalls the aircraft. It could also cause weakening or loss of communication (Novotny, 2005).
There are two types of ice formation or accretion. Rime ice forms when extra cool water drops freeze upon contacting the sub-zero surface. The small droplets instantly freeze trapping air. Rime ice is rough and brittle having a white color from afar. Rime ice collects on the edges and can harm aerodynamics obstructing air intakes by the engine. Rime has no particular shape but coats the edges roughly. As development advances it protrudes into the air although there are limitations on the size of the “horn” it forms (Ellis, 2003).
Under such parameters, it is found that ice, glazed or clear; tends to accumulate with the help of bigger cold droplets that take more time to solidify. The ice is clear and transparent. Freezing is relatively slow allowing the even spread of the water. It causes the formation of an ice sheet that may not be easily detected. The speed of solidification of the droplets depends on the size of the globules. A larger water globule takes more time to freeze and the ice becomes more transparent. Sometimes when the weather is extreme the size of ice on the edge may look like a “double ram’s horn” at various angles and on multiple locations on the exterior of the aircraft. Glaze ice being large it has more of a structure than rime ice (Novak, 2000).
Mixed or cloudy ice is the name given to ice formation that has the appearance of both rimes as well as clear ice. It is the most common form of accretion with either of the two characteristics dominating. There are other types of ice formations – supercooled large drops, runback ice formation on the tail and wings of the aircraft, and inter-cycle ice that forms between cyclic activation of a mechanical or a thermal de-ice system. Thus ice formation is a vital part of aerodynamics – a complex issue because of the various types of ice formation and the dangers connected with it (Fisher, 2006).
De and or anti-icing operations on the ground have three targets – removing any frozen or even semi-frozen dampness from the important exterior parts of the aircraft on the ground prior to taking off, providing protection to these places from the same problem from the time the treatment is done on the ground to the time of the plane being airborne and thirdly removing of any frozen or semi-frozen dampness from the intakes of the engine and fan blades and providing future protection before taking off. Thus the airplane has to be first thoroughly inspected for any frozen ice already sticking to the surfaces and wherever found it has been cleaned by using the proper kind of de-icing fluid (Hartwell, 2008).
Secondly, a meticulous note has to be made of the current weather conditions. If fresh ice or snow adheres to the surface of the frame of the aircraft or it is apprehended this will occur when the plane takes off, then the proper anti-icing fluid has to be applied by the ground crew engaged for this purpose. After taking off the fluids applied on the ground have no effect. The process of ground de-icing and anti-icing targets three goals – removal of any frozen moisture from the outsides of the aircraft on the ground that is ready to take off, protecting these areas from being frozen while taking off, and the removal of any such freeze from intakes by the engine and blades of the fan and also ensuring that these regions are protected before getting airborne. For this purpose ground de-icing and anti-icing fluids have to be used (Switzenbaum, 2004).
The next step is to study the existing weather conditions. If there is the possibility of further freezing while on the ground and immediately after taking off, then the appropriate anti-icing fluid would have to be applied. The fluids are so designed as to give the required protection no later than the time the aircraft is airborne. It means that the fluids applied on the ground are no protection against the risks that may arise after the plane takes off.
Aerodynamics requires that the frame of the aircraft is free from frost immediately prior to taking off. This is referred to as the concept of clean-aircraft. If this is not done and frost or semi-frost adheres to the frame when the plane is airborne it may cause sudden control loss soon after take off. Ice adhering to the inner wings may be ingested by the engines causing sometimes thrust loss – either partial or total. Adverse effects on engine operations may cause fire outbreaks (Davis, 2004).
The first thing is to thoroughly inspect the frame of the aircraft to find traces of frost or semi-frost. The surface temperature has to be noted – it is as important as the prevailing outside temperature. The temperature relating to the weather conditions after the beginning of the treatment would also have to be anticipated to find out if anti-ice treatment is required. Thirdly the correct de-icing and or anti-icing fluids would have to be applied. The holdover-time has to be determined so that the crew does not attempt to take off within that period. The note must be taken that if weather conditions change so too may the hold-over time. If applicable hold-over time is not there then take-off cannot be allowed (Cancilla, 2003).
Some of the fundamental questions that would be asked are:
- How would you assess potential regulatory impacts?
- How would you use thermal blankets for B737 and 320?
- How would you use solar radiation in the deicing process?
- How would you evaluate the geographical location of an airport?
- In-pavement deicing, which is a more useful method, mechanical or chemical?
The team is expected to detect snow or slush within the nacelle of the engine but it may be impossible by resorting to the usual visual inspection. Removal of the frost may prove to be equally difficult. Therefore prior protection has to be taken to prevent the ingress of ice and snow by the use of covers and plugs. These have to be perfectly made secure and recorded in the logbook. Failure to de-icing may cause the failure of the plane to take off, to lose control immediately after it, or during retraction of the flHigh-speed-rejected-take-off off may result due to failure of de-icing while on the ground. It may also result in forced landing for failing to shed ice from wings. These happen when it has not been properly ascertained if there is frozen moisture (May, 1999).
Formation of frost on important surfaces of the aircraft – wings, pro,pellers and stabilizers may change the airflow and reduce the lift while increasing the drag. The extra weight of the ice adds to the aircraft’s total weight increasing the lift that is required for taking it off the ground. Even small quantities can lead to grave consequences. De-icing fluids melt the frost. On top of these anti-icing fluids prevents, for a certain period of time, the formation of new ice on critical parts of the aircraft. The de/anti-icing operations are done as close as is possible from the taking off time (Kent, 1999).
Deicing is a very important mechanism in airport maintenance. A well-developed and properly research and the formulated de-icing system is a real-life saver. Two kinds of accidents can occur during flights because of ice forming on the frame of the aircraft. The Aircraft eats up the power reserves of the plane. Subsequently, it cannot maintain altitude and or speed. While flying over mountainous regions it may collide with the peaks. Secondly the wings and tail need extra protection from ice formations because if the ice load becomes abnormal there is a danger when the plane attempts to move with the extra load. Thus, it is important to carry on research regarding this problem for a long-termed benefit in a well formulated transport management system. It is not about just techniques, it is about life-saving applications and thus it is important for the team to prepare perfectly for the job. Though there are only 8 members in the team maintaining 25 aircrafts, it is important to prepare them for the worst condition.
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Cancilla, D.A. (2003). Studies of the environmental fate and effect of aircraft deicing fluids: Detection of 5-methyl-1H-benzotriazole in the fathead minnow. Environmental Toxicology and Chemistry, 22(1), 134-140.
Davis, W.B. (2004). Aviation law: cases and problems. NY: W.S. Hein & Co.
Ellis, J.B. (2003). Transport and the Environment: Effects of Temperature on Water Quality. Water and Environment Journal, 11(3), 170-177.
Fisher, D. (2006). ‘The acute whole effluent toxicity of storm water from an international airport. Environmental Toxicology and Chemistry, 14(6), 1103-1111.
Hartwell, S.I. (2008). Toxicity of aircraft de-icer and anti-icer solutions to aquatic organisms. Environmental Toxicology and Chemistry, 14(8), 1375-1386.
Kent, R. (1999). Canadian water quality guidelines for glycols-An ecotoxicological review of glycols and associated aircraft anti-icing and deicing fluids. Environmental Toxicology, 14(5), 481-522.
May, E.B. (1999). Aircraft de-icer and anti-icer: Problems. Environmental Toxicology and Chemistry, 13(7) 1179-1182.
Novak, L.J. (2000). Acute toxicity of storm water associated with de-icing/anti-icing activities at Canadian airports. Environmental Toxicology and Chemistry, 19(7), 1846-1855.
Novotny, V. (2005). Urban and highway snowmelt: minimizing the impact on receiving water. NY: Water Environment Research Foundation.
Switzenbaum, M.S. (2004). Best management practices for airport deicing stormwater. Amherst: Water Resources Research Center.