Throughout its history, the aviation industry has had a close but unpleasant relationship with the vagrancies of weather (Vickers et al., 2001). Indeed, it has been proved that weather is the single largest contributor to delays and a foremost factor in aircraft disasters and incidents, implying that real-time weather information is substantially critical for hazardous weather avoidance in aviation operations (Witiw, Lanier & Crooks, 2003).
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Weather continues to exact its toll on the aviation sector, particularly when this argument is viewed in the context of past accidents that have been reported in mainstream media as caused by either meteorological hazards or a combination of human factors and weather elements (Broc et al., 2005; World Meteorological Association, 2007). The present paper critically discusses some of the well known meteorological hazards in the aviation industry.
Meteorology has been described as “…the science of the atmosphere, a sea of air that is in a constant state of flux” (Vickers et al., 2001, p. ix). Within this science exists a wide allay of weather/climatic conditions arising from natural interactions with other factors, products and byproducts, but which triggers a set of hazards that may prove disastrous to the aviator who must operate within the precincts of the atmosphere (Simpson et al., 2002).
It is reported in the literature that no one is immune to the everyday oscillations of these meteorological hazards as they sweep across huge sections of the globe before dissipating (Vickers et al., 2001).
Meteorological Hazards in Aviation
Available literature demonstrates that there exists a multiplicity of weather conditions that qualify as hazards in aviation due to the scope and context of the dangers they present to the industry (Broc et al., 2005). Some of the most predominant ones include icing, volcanic ash, poor visibility, windshear, heavy rains, lee waves, fronts, thunderstorms, cold weather and deformation zone (World Meteorological Association, 2007). This section samples a few of these meteorological hazards in aviation.
Witiw et al (2003) describe the windshear as “…a sudden shift in wind direction, velocity, or both” (p. 131). These authors also report that the most aggressive expression of the condition occurs in a microburst, which is an intense downburst of cool air generated by, or released from, a large convective cloud. The World Meteorological Organization (2007) defines windshear as “…layers or columns of air, flowing with different velocities (i.e. speed and/or direction) to adjacent layers or columns” (p. 1).
Windshear is a foremost hazard for low, slow flying aircraft in either the approach or departure phases due to the complicated wind patterns occasioned by the downdrafts. As the aircraft glides through the microburst it stumbles upon intense headwinds accompanied by a substantial increase in aerodynamic drift and successive severe downdrafts, ultimately causing it to experience a rapid loss of lift and crash into the ground (Witiw et al., 2003).
Consequently, some of the detrimental hazards caused by windshear include: 1) loss of aerodynamic lift and airspeed, making the aircraft to plunge into the ground before corrective action is taken by the flight crew, 2) turbulence especially in light aircraft, and 3) structural damage to the aircraft (Witiw et al., 2003; World Meteorological Organization, 2007).
In the United States, the National Transport Safety Board (NTSB) database reveals that nearly 250 accidents involving U.S. aircrafts have been attributed to windshear, with 30 of them reported as major (Witiw et al., 2003).
Although one of the most beautiful atmospheric phenomenon (Harding, 2011), extant literature demonstrates that “…no other weather encountered by a pilot can be as violent or threatening as a thunderstorm” (Vickers et al., 2001, p.34). Indeed, thunderstorms generate more threats to the aviation industry and it is always important for the flight crew, air transport safety agencies, meteorologists and other interested stakeholders to not only understand their scope and context, but also how to deal with them effectively.
Thunderstorms are generated by the coming together of several ingredients, including: 1) unbalanced air mass, 2) atmospheric moisture in the low levels, 3) some triggering mechanism, e.g. daytime heating or upper level cooling, and 4) other related meteorological vagrancies such as windshear (Vickers et al., 2001).
These ingredients interact through a process called convection (transport of heat energy) to produce thunderstorms that basically attempt to correct the imbalance generated when the atmosphere becomes heated unevenly (Harding, 2011).
It is important to note that there exist different types of thunderstorms that affect the aviation industry. Some of the most common types of include: 1) air mass thunderstorms – form within a worm, moist air mass and are non-frontal in character, 2) frontal thunderstorms – form either as a result of a frontal surface lifting an unbalanced air mass or a stable air mass becoming unbalanced due to the lifting, 3) squall line thunderstorms – aggressive combinations of strong winds, hail, rain and lighting, 4) orographic thunderstorms – occur when moist, unbalanced air is forced up a mountain slope at high pressure, and 5) nocturnal thunderstorms – develop during or persist all night (Vickers et al., 2001).
Thunderstorms have the capability to generate hazards that can cause untold suffering in the aviation industry. For instance, “…all thunderstorms can produce severe turbulence, low level windshear, low ceilings and visibilities, hail and lighting” (Harding, 2011, p. 1).
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It is not uncommon to hear news of aircraft that get lost in severe thunderstorms or helicopters that get struck by lightning, implying that each of these conditions can be potentially catastrophic (Broc et al., 2005). Other hazards generated by thunderstorms include ruthless clear icing, extremely profound precipitation, and dangerous electrical releases within and near the thunderstorm cell (Vickers et al., 2001; World Meteorological Organization, 2007).
It is reported in the literature that reduced visibility is the meteorological element which impacts aviation operations the most through cancelled flights, accidents as well as incidents (Vickers et al., 2001).
These authors posit that the aviation industry uses various types of visibility, which include: 1) horizontal visibility – the furthest visibility achieved horizontally in a particular direction by referencing objects or lights at known distances, 2) prevailing visibility – the ground level visibility which is common to one-half or more of the horizon loop, 3) vertical visibility – the maximum visibility achieved by looking vertically upwards into a surface-based impediment such as mist or snow, 4) slant visibility – visibility achieved by looking forward and downwards from the cockpit of the aircraft, and 5) flight visibility – the standard range of visibility at any given time forward form the cockpit of an aircraft in flight.
Reduced visibility is caused by a multiplicity of factors, including lithometers (dry particles suspended in the atmosphere, such as haze, smoke, sand and dust), precipitation, fog (radiation fog, frontal fog, steam fog, advection fog and ice fog), as well as snow squalls and streamers (Vickers et al., 2001).
As already mentioned, low visibility leads to flight cancellations, fuel wastage as aircraft is unable to land in designated destination, aircraft damage in midair collisions, and deaths resulting from aircraft accidents (Watson, Ramirez & Salud, 2009).
The 2011 massive flight cancellations in Europe that were triggered by airborne volcanic ash from the Grimsvotn volcano in Iceland prove that volcanic ash is a major hazard to aviation safety at all levels. Indeed, “…like fine-grained mineral dust, volcanic ash affects radiative forcing and climate, public health, vegetation, and can cause property damage and disruption to community infrastructure” (Hadley, Hufford & Simpson, 2004, p. 829).
The major problem with volcanic ash emanates from the fact that onboard aircraft radars are unable to detect concentrated ash within or near eruption plumes, leading to life-threatening encounters, huge losses in flight cancellations, and aircraft damage (Simpson et al., 2002).
The damage caused by volcanic ash often calls for expensive repairs or total equipment replacement, thus it is of outmost importance for flight crew to ensure total avoidance of the ash for flight safety. What’s more, the pumice material contained in volcanic dust acts to abrade the aircraft’s leading edges (i.e. wings, struts, and turbine blades) to a point where the aircraft can cause a fatal accident if no replacement is done (Vickers et al., 2001).
Icing or Icy Weather
Schreiner (2007) acknowledges that “…icy weather, including ice pellets and cloud droplets that freeze on contact, affects air travel all over the world, especially during colder months” (p. 152). Aircraft icing takes place when supercooled water droplets from the atmosphere hit an aircraft whose body temperature is colder than 0oC, crystallizing into ice and occasioning serious detrimental effects that often expose an aviator to the real probability of causing an accident (World Meteorological Association, 2007).
The two most important meteorological factors that affect icing include liquid water content of the cloud and temperature structure in the cloud.
Some of the detrimental effects caused by icing include: 1) restriction of visibility as windshear glazes over, 2) disturbance of the smooth laminar air flow over the aircraft wings, occasioning a decrease in lift and an increase in the stall speed, 3) increase in aircraft weight and drug, hence decreasing fuel efficiency, and 4) incomplete or absolute blockage of pitot heads and static ports, thereby allowing erroneous instrument readings (Vickers et al., 2001). A study conducted by the NTSB demonstrates that approximately 819 people lost their lives in accidents linked to in-flight icing between 1982 and 2000 (Schreiner, 2007).
Although there is no agreed upon definition regarding rainfall intensity, heavy rainfall is defined in the literature as rates in excess of 4 mm per hours, while heavy showers are perceived as rates in excess of 10 mm per hour (World Meteorological Association, 2007).
Heavy showers, which are often associated with thunderstorms, qualify to be seen in the context of a meteorological hazard to aircraft due to their capacity to not only reduce physical and canopy/windscreen visibility, but also permit water ingestion into the cabin/cockpit/engine partitions of light, non pressurized aircraft, thereby endangering the effective and efficient operations of electronic equipment within the aircraft.
There exists a possibility for aircraft turbine engines to ‘flame out’ and cause destructive effects under conditions of extreme rainfall and subsequent water ingestion (World Meteorological Association, 2007). Additionally, it has been reported that intense rainfall affects aircraft braking mechanism and may cause the aircraft to skid off the runway during takeoff and landing (Vickers et al., 2001).
Duststorms and sandstorms, according to the World Meteorological Association (2007), are regions of raised dust and sand due to intense wind activity. The particles are propelled to different altitudes depending on the speed, instability and resolution of the wind flow, in line with the principle that smaller and lighter elements are lifted more readily and to much more elevated altitudes than weighty elements.
Duststorms and sandstorms bring potentially destructive outcomes in aviation, such as reduced visibility, reduction of engine power in the event of dust and sand ingestion into aircraft engines, costly repairs, and aircraft crash in the event of a complete engine lockdown (Hadley et al., 2004; World Meteorological Association, 2007).
The paper set out to critically discuss some of the well known meteorological hazards in the aviation industry. It has been sufficiently demonstrated how normal meteorological processes, such as windshear, thunderstorms, visibility, volcanic ash, icing, heavy rain, as well as duststorms and sandstorms, operate to become potential hazards in aviation.
The potentially destructive outcomes arising from the different meteorological processes have been discussed at length, with the results demonstrating that many meteorological hazards lead to loss of life through aircraft accidents, loss of profits through frequent flight cancellations and rescheduling, loss of aircraft through structural damages, as well as costly repairs.
It should therefore be the task of meteorology experts to conduct intense awareness campaigns in the aviation industry regarding the serious issues posed by meteorological vulnerabilities.
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