Freezing rain is a term, denoting a natural phenomenon, which occurs when the temperatures reach the freezing marks. Although freezing rain bears a great resemblance to such precipitations as sleet, hail and ice pellets, it also has some unique features and characteristics. Thus, freezing rain consists of liquid droplets solely. When the surface temperatures remain low, the water drops gradually freeze as they pass the upper layers of the atmosphere (Baum, 2007). When these drops reach the surface, they resemble the ice drops and present a serious threat to the surroundings. In some cases, the ice droplets can accumulate on the surfaces and form the thick layers on them. Such a situation can harmfully damage the vehicles’ safety and security of transportation (Kocin & Uccellini, 2013).
In fact, freezing rain causes significant traveling problems and difficulties by ruining the power lines, threatening the safety of roads and airways and breaking the tree limbs. Many air accidents have occurred as a result of freezing rain or ice storms. Mainly, freezing rain damages the system of control of the airplanes, promotes the blurred vision and reshapes the format of airfoils and wings. All these circumstances harm the flight control system and cause difficulties while landing. Thus, modern airplanes need to have the effective systems of anti-icing equipment in order to react to freezing rain and storms appropriately (Dingle & Tooley, 2013).
By causing serious damages on different levels, freezing rain is regarded as one of the most harmful and serious precipitations. This phenomenon negatively affects the systems of communication and connection as well as creating considerable difficulties for the secure travelling and vision. This paper aims to investigate freezing rain as a natural phenomenon and analyze its negative impacts on air safety.
Causes of Freezing Rain
Freezing rain is a winter phenomenon. It happens because of the differences in the temperatures between various layers of atmosphere. Formed in the relatively warm surroundings, the liquid drops gradually freeze in the process of falling down to the Earth surface. The shift in temperatures coverts the water into ice and promotes the emergence of freezing rain. From this standpoint, freezing rain looks similar to sleet. However, the difference consists in the fact that the drops of freezing rain have no time to freeze completely before reaching the surface. As a result, they exist in a form of liquid droplets, on the contrary to sleets and hails (Baum, 2007).
Moreover, it is important to mention that freezing rain usually witnesses considerable climate changes on a certain territory. For example, they often occur at the end of winters, when the general cold climatic conditions change into the warmer ones. Additionally, freezing rain is a result of low-pressure system movement and replacement of the high-pressure one. Correspondingly, not only surface temperatures but also indicators of air pressures influence the emergence of freezing rain. In other words, it is a natural phenomenon which calls for a certain arrangement of climatic conditions and circumstances (Baum, 2007).
The main factor determining freezing rain is the depth and size of the sub-freezing layer of atmosphere. It was already mentioned that too big layers create ice pellet and sleets, immediately forming the ice balls. On the contrary, a very shallow sub-freezing layer will provide the liquid drops with too little time to cool down (Baum, 2007). Correspondingly, the drops will fall in a form of rain.
Thus, an essential condition for the creation of freezing rain consists in the middle depth of the sub-freezing layer. The drops have to remain super-cooled at the point of reaching the Earth. When the droplets interact with any surfaces, including trees, roads, vehicles or communication means, they immediately freeze and form an ice layer on it.
The danger of freezing rain consists in its capacity to store on the surfaces and form thick layers of ice. It is estimated that a freezing layer of more than 0.5 inch is able to create long-lasting damages and disruptions in the work of communication and transportation systems (Kocin & Uccellini, 2013). Therefore, the regions where freezing rain is likely to occur should develop a branched system of anti-icing protection in order to overcome the effects of this precipitation and restore normal functioning of the urban infrastructures.
Effects of Freezing Rain
Without doubts, freezing rain brings enormous harmful effects, which can even lead to the fatal consequences. Freezing rain tends to cover the surfaces with the ice, considerably increasing the weight of objects. If the accumulated amount of ice becomes thick and heavy, it can lead to negative outcomes, causing troubles for the free transportation and movements (Murphy, 2009). It is also essential to mention that freezing rain causes enormous threats to the safe travelling as it makes the roads and airways dangerous and unsuitable for transportation.
Freezing rain leads to the deterioration of visibility, limitation and blur of vision, causing difficulties with orientation in space. Unlike snow and sleet, freezing rain forms an invisible layer of ice on the surfaces. When these layers become too thick and heavy, they degrade the vision, making any transportation hazardous and insecure. Such layers are called graze, and their main threat consists in the limitation of sight (Kocin & Uccellini, 2013). Obviously, such climatic conditions are harmful for the air flights since they strongly disrupt the visibility. Nevertheless, blurred vision is not the only negative outcome of freezing rain experienced by the aircraft.
The most significant threat consists in the reshaping of planes’ units under the influence of heavy ice layers. The matter is that freezing rain tends to create immediate structural icing on the external elements of planes. Usually, it is a problem of small aircraft and helicopters, which have no anti-freezing equipment and cannot respond properly to the harmful effects. However, freezing rain can also affect modernized well-equipped crafts (Dingle & Tooley, 2013).
The influences of freezing rain on the aircraft are two-fold. On one hand, it increases the weight of airplanes because of the formation of thick icing layers. The ice coverage leads to the phenomenon known as “frozen wings”, which contributes to the reduction of plane’s plasticity and performance. Nevertheless, the modern crafts can cope with this problem and eliminate its negative effects. More significantly, freezing rain changes the shapes of the airfoils, reducing lift and increasing the drag. Such changes make the planes unable to demonstrate flexible performance and maintain the required level altitude. Additionally, this problem contributes to the growth of stalling speed and reduction of the planes’ plasticity (Dingle & Tooley, 2013).
The other difficulty, connected with freezing rain, is the impossibility to conduct maneuvers easily and rapidly. In fact, it is enough for aircraft to move into the area with warmer temperatures in order to remove the ice layers and return the previous flexibility (Dingle & Tooley, 2013). Nevertheless, this maneuver may be a confusing task to complete as freezing rain appears with the external temperatures’ inversions, which make it impossible for the crafts to manage to move to the warmer zones. This task is potentially difficult, despite the amount and thickness of the ice layers.
Aircraft Accidents Caused by Freezing Rain
Throughout the history, there were several air accidents caused by freezing rain. Freezing rain caused the crash USAR Fight 405 in 1992. According to NTSB (1993), the poor weather conditions (snow, rain and fog) damaged the airflow of jet and led to a huge accumulation of ice on plane’s wings and airframe. As the pilots did not implement any effective deicing procedures, the plane crashed soon after the liftoff. The report informs about 21 deaths, including the captain of plane and members of crew. The main cause of this crash consisted in the pilots’ unawareness of the amount of ice, accumulating on the external parts of plane. Correspondingly, they did not take any measures to prevent the catastrophe.
In 1994, American Eagle Flight 4184 faced the poor weather conditions caused by the ice storm and failed to land successfully in a planned airport (NTSB, 1994). On the account of freezing droplets and ice layers, which immediately covered the external units of the craft, the plane was disconnected from its autopilot system and communication and control means. The cover of ice on the wings made it impossible to take the right measures for the successful landing. As a result of this effect, the plane fell on the field, killing all passengers and members of the crew (Dingle & Tooley, 2013).
In 2001, the turboprop Cessna 208, the Hageland Aviation flight was crashed in Alaska because of freezing rain and limited visibility. According to the official statements, the plane flew in the area of ice storm and lost control over the pilot system. Respectively, it failed to land appropriately. This accident led to four deaths and significant material damages (Mason, 2010).
It is also said that ice droplets have caused the tragedy of the Air France Flight 447. In 2009, this plane crashed into the Atlantic Ocean, killing all passengers and members of crew. After a range of investigations, the experts have suggested the version, claiming about the crucial role of ice drops. According to this theory, the ice drops accumulated on the plane’s tubes and led to the disconnection of the autopilot. As a result, the pilots lost control and could not maintain the required altitude and angle of flying. In fact, a number of reasons led to the tragedy. However, it is impossible to underestimate the role of natural phenomenon in this crash as well (Ranson, 2009).
Overall, freezing rain has caused several serious aircraft accidents, which led to the fatal consequences and huge financial disruptions. Such statistics witnesses the danger of this natural phenomenon and necessity to install the anti-icing equipment. In fact, there exist certain measures, which help to overcome the negative effects of freezing rain and increase the security of aircraft.
How to Avoid and Resist the Effects of Freezing Rain
To start with, the modern airplanes have to be equipped with the anti-icing and deicing means. The anti-icing equipment helps to prevent icing and freezing of the external units of planes while the deicing means help to overcome the existed impacts of freezing rain and ice storms. Commonly, the anti-icing equipment includes the propeller anti-icers, wings’ deicer, inflatable rubber strips attached to the upper sides of the wings, windshield anti-icers and other anti-icing systems. All of those elements aim to increase plane’s flexibility, turning on the option of copilot and preventing the accumulation of ice on the parts of aircraft (Dingle & Tooley, 2013).
In addition, the safety rules suggest the following advice, which help to recover from the harmful impacts of freezing rain. The first step toward overcoming freezing is the reduction of power or its maintenance on the required altitude. It is also advised not to increase the general speed of aircraft and conduct the slow maneuvers in order to fly away from the dangerous zone. Moreover, it is important to connect with the support service and listen to the further advice connected with following routes and movements of flying. It is essential to avoid panics and act moderately and reasonably to find the optimal ways out.
Additionally, the contemporary aviation widely implements the anti-icing or deicing fluids, which prevent the freezing of aircraft’ parts and accumulation of ice droplets. There exist various types of anti-icing fluids, in accordance with the field of their usage, purpose and their validity. Thus, there are fluids which guarantee short and long-lasting effects as well as substances, which help to break different degrees of ice coverage (FAA, 2012)
To sum up, freezing rain is a dangerous natural phenomenon, which brings plenty of harmful effects to the surroundings. It occurs under the range of successive influences of high and low temperatures and emerges in a form of freezing liquid droplets. Freezing rain tends to cover different types of surfaces with the ice layers, causing damages to the latter. It is extremely harmful for the airways and aircraft. Freezing rain and ice storms have contributed to a range of air accidents by limiting the visibility, freezing the external units of planes and reducing their flexibility and performances. Very often, freezing rain and ice storms lead to the loss of connection and communication means. Obviously, such a situation demands the establishment of anti-icing equipment and consideration of preventive measures.
Besides the conventional anti-icing and deicing equipment, the ways of overcoming the effects of freezing rain may include such preventive measures as thorough preparation, identification of possible alternative airways, consideration of the weather forecasts and climatic peculiarities of the regions of flying, installation of the anti-icing systems and the inspection of the aircraft serviceability.