Introduction
Storms usually pose a significant threat to aviation due to the downbursts and low-level wind shear associated with them. These weather events can negatively impact airlines because they cause sudden wind velocity and direction changes, which are responsible for severe flight schedule disruptions. Storms and the rapid shifts of winds that accompany them often make it challenging for pilots to control the aircraft, make air travel uncomfortable for passengers, or cause a crash.
When planes encounter these damaging gusts, they cannot land or take off, re-route around storm cells, or divert to neighboring airspace. In addition, extreme winds near airports may also impede ground operations until they subside. According to a report, these disruptive weather patterns contribute to about 75.78% of air traffic delays in the aviation industry (Federal Aviation Administration, 2022). Downbursts and low-level wind shear are linked with microbursts, which are hazardous to aircraft landing or taking off.
Hazards of Microbursts and Wind Shear
Extreme wind patterns can threaten aviation in different ways. In this case, downbursts caused by storms generate a strong, sudden, and rapidly descending wind, causing an outflow of damaging, straight-line forces when they come in contact with the earth’s surface. These destructive gales form when raindrops mix with drier air, cooling and increasing their density and causing them to sink faster to the ground (Solari, 2020). The effects caused by downbursts may pose a significant risk to aircraft, especially during landing and takeoff. The downbursts are either micro or macrobursts (Romanic et al., 2022). Regardless of their nature, these weather events are dangerous for flights.
Storms also cause low-level wind shear and can be highly hazardous to aviation. This is due to abrupt changes in wind direction or speed over a short distance near the ground. Apart from terrain or topography, microbursts are linked with low-level wind shear because they can initiate sudden changes in wind speed and short-distance direction (Hon, 2020). Thus, unexpected wind flow changes across microbursts can cause an aircraft to stall or increase its descent rate.
Microbursts can cause severe turbulence for aircraft and even knock them out of the sky. Microbursts encompass localized and small-scale dense air referred to as downdraft, an intense downward force. As indicated earlier, heavy precipitation creates a downdraft through drag and cooling, forming a microburst (Childs et al., 2021). When the downdraft comes in contact with the earth’s surface, it fans out in all directions from the impact point and subsequently curls up from the ground to create a vortex ring. This dense cold air may descend at about 1,000 to sometimes 6,000 feet per minute, hit the ground, and spread (O’Connor & Kearney, 2019).
Consequently, this often produces a strong wind near the Earth’s surface. In this case, a microburst can impact an area four kilometers or less in diameter (McCarthy et al., 2022). In addition, in most cases, its intensity can reach 45 knots immediately after contact with the ground and usually dissipates about 15-20 minutes after hitting the ground (McCarthy et al., 2022). Microbursts may occur anywhere, usually during thunderstorm seasons, and if one develops, it can cause significant problems for pilots.
Due to its small scale yet powerful nature, a microburst can occur in wet and dry weather events. Wet microbursts typically form when a layer of dry air collects above a dense layer of humid air (Nechaj et al., 2019). In this case, the strong updrafts within convective clouds cause the air to become saturated with moisture, rapidly falling the moist air towards the ground and creating strong winds.
Conversely, a dry microburst, as the name implies, is common in climates where a moist air layer is 2 to 3 kilometers thick (Nechaj et al., 2019). Since the air is dry enough, the condition allows precipitation to evaporate when it reaches the ground, creating a dry microburst. These air currents often descend rapidly, and when they hit the ground, they spread out in all directions, sometimes at a speed of more than 70 kilometers per hour (Nechaj et al., 2019). The main distinguishing feature between wet and dry microbursts is the environment in which they are formed; nevertheless, they are both dangerous to aviation.
Microbursts are intense downward winds that are a significant threat to aircraft. Microbursts near the ground are most dangerous to planes flying at low altitudes, especially during landing and takeoff (O’Connor & Kearney, 2019). A pilot approaching a microburst may initially experience an intense headwind, resulting in an increased indicated airspeed (IAS) reading, which may lift the aircraft above its intended flight path (Cutler, 2018).
Consequently, this may force the pilot to decrease the power to maintain a set airspeed, which is risky because the wind may quickly turn into a tailwind once an aircraft approaches a microburst. These rapid changes in tailwind and headwind are expected during the microbursts encounter and can decrease IAS and lift (Cutler, 2018). This may cause an aircraft to lose considerable altitude and even be at risk of crashing to the ground. A microburst that endangers aircraft lasts 5 to 20 minutes and is confined 100 feet above the ground (Nechaj et al., 2019). The downward pull of microbursts can escalate the likelihood of an aircraft stalling, making it difficult for the pilot to regain control.
Historical Incidents and Mitigation Measures
Microbursts have always been considered to be a major threat to aviation. A microburst has been described as strong enough to thrust a plane on the ground but small enough to remain undetected through weather observations. It has a short lifespan, a small spatial extent, and a distance above the ground (Nechaj et al., 2019).
In the past, microbursts have contributed to various catastrophic commercial airline crashes. Some include Flight 806 and Flight 66, belonging to Pan American World Airways and Pan Eastern Air Lines. These planes crashed in 1974 and 1975 while attempting to land at Pago Pago and John F. Kennedy Airport, respectively (McCarthy et al., 2022).
Another incident involved Flight 191, a Delta Air Lines plane, which fell at the Dallas–Fort Worth Airport, Texas, in 1985 (Nechaj et al., 2019). Additionally, most recently, in 2016, a modern Boeing 737 airplane crashed, killing all the passengers onboard after encountering wind shear while trying to land in Rostov, Russia (O’Connor & Kearney, 2019). These incidents show how it is essential to closely monitor microbursts during storms and adopt effective measures to increase protection against their impacts.
Microbursts can be avoided to prevent catastrophic accidents through various mechanisms. For example, different airfields use Terminal Doppler Weather Radar (TDWR), Low-Level Windshear Alert Systems (LLWAS), or Weather Systems Processor (WSP) (O’Connor & Kearny, 2019). These devices can detect a drastic change in wind direction and speed, as well as a microburst, by measuring the wind shear. Similarly, the aviation sector has adopted the best practices by making microburst hazards a standard part of training in small airfields used by light planes. This is because some systems are only found in Class B or C airports that serve significant airline traffic.
Furthermore, pilots are educated to utilize visual cues in the cockpit to detect any possible shift in wind direction and speed before landing or takeoff. Training enables aviators to be well-prepared to escape or maneuver around microbursts. Pilots are also equipped with the expertise to maintain a minimum ground speed, ensure a minimum level of energy to the aircraft, and ensure proper thrust management during an encounter with microbursts. Lastly, it is vital to wait out microbursts since they are short-lived, with peak winds lasting only a few minutes.
Conclusion
In conclusion, a microburst is one category of a downburst and the primary source of low-level wind shear. Although microbursts are small and typically no more than four kilometers wide, they can pose a severe hazard to aviation. These sinking air masses can push airplanes from the sky during landing or takeoff.
Reports show how these meteorological events caused several commercial airline crashes in the 1970s, early 1980s, and even recently. However, meteorological systems, such as TDWR, LLWAS, and WSP, can aid in detecting and avoiding microbursts as they occur. Similarly, best practices in aviation, including safe navigation and waiting for these wind events to subside, can help prevent dangers associated with microbursts.
References
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