With less obstacles in the air and more space to play around with it is continuously widely accepted that this current modern wave of aviation is one of the safest modes of transportation in the world. There is one major exception however, atmospheric weather, its uncontrollable nature can often lead to extremely dangerous events and in the world of aviation it is deemed to be of great concern. This report will extensively cover both cases Air France Flight 447 and Korean Air Flight 801 in depth regarding the accident report and more specifically the weather conditions situated during the time.
Air France Flight 447 was an international scheduled passenger flight flying from Rio de Janeiro to Paris and unfortunately crashed before reaching the destination due to a failed stall recovery killing 228 passengers and aircrew, it is the deadliest accident in Air France history. It is reported that the aircraft crashed due to inconsistencies with the airspeed and the presence of large thunder storms across the Pacific Ocean. Thunderstorms are generally an intense and short-lived weather phenomenon, due to its actively high energy output, it consists of an abundance of variables such as thunder, lightning, dense clouds, heavy rain, hail and strong winds. These storms form when amounts of warm air rise in an upward fashion into the cooler parts of the atmosphere, condensing the moisture which soon develops into what is known as a cumulonimbus cloud. Large ladders of cooled air then plummet towards the earth generating powerful downdrafts and when striking the ground horizontal blows also. Simultaneously positive and negative charges gather on the cloud matter, effectively accumulating into a large enough charge to produce lightning. When lightning is discharged it heats the air it passes through so powerfully that shock waves are generated which is the result of thunder.
Vertical atmospheric motion is quite similar to turbulence, in the Earths wind systems large volumes of ascending and descending air fluctuate violently and this pattern is parallel with thunderstorms as they are unstable to vertical motion. This instability will occur whenever two volumes of differently temped air overlap each other, for example the most common variation, when warm air is covered by cooler and denser air. As stated earlier under these conditions an upward motion of air then initiates an unstable atmosphere and this can be generated in several ways. Most commonly the mechanism responsible is the heating of the land surface and the adjacent layers of air, the heat radiating off the ground forces the lower layers of air to increase in temperature and thus drive the air upwards. Typically, the clouds associated with thunderstorms are huge cumulus clouds that break out and develop vertical towers of unstable rising air mass. In turn the cumulus clouds merge together forming what is known as a congestus cloud, gaining even higher altitude and then soon into the final form the cumunolimbus cloud where heavy rainfall begins, starting the thunderstorm. The three different types of thunderstorms are the single-cell, the multicell and the supercell and each variation consist of a number of distinctive attributes such as structure and circulation pattern. The single-cell has a limited life cycle with little potential to grow, the cloud generally forms, produces fair downpour and quickly decays as the descending air strangles the original warm inflow. The duration of this storms life is around an hour and almost every time they rarely produce any alarming dangers. As for the multicell, this common thunderstorm is rather successful and maintains overall strength through multiple updraught pulses, hence the name. Due to the condensed area in which the pulses perform the storm becomes quite uniform overtime.
Finally the supercell, this violent thunderstorm can sustain itself for many hours, its appearance is systematic and the clouds highly organized structure amplifies and helps manifest into a very strong storm.
The Korean Air flight 801 is another prime case displaying how much weather can have an effect on aircraft. The plane departed from Seoul- Kimpo International Airport for Guam on August 5 1997 with 14 flight attendants and 273 passengers. It is reported that the flight experienced strong turbulence, winds, and heavy rain throughout the duration of the flight and visibility was extremely low forcing the pilots to rely on their instruments. This led to the unfortunate event where a total of 254 people died after a failed landing 5.6 kilometers short from the runway. The crew noted that the aircraft was descending quite steeply yet couldn’t make a visual of the airport. Even after protest the pilots continued to descend and at 1:42am the plane made impact with the ground crashing into a hill. One survivor remained, a 36 year old man Hyun Seong Hong, stated that the crash happened so quickly that the passengers “had no time to scream”.
In stationary air, two factors that ultimately decide the amount of pressure that a gas delivers are temperature and density. Their relationship is called the ‘ideal gas law’ and it can be displayed by the equation, pressure = temperature x density x constant. Any change in the variables will cause a predictable chain change, effectively generating wind. Wind is the result of differences in horizontal air pressure, Due to this, the difference in air density allows air to flow from higher pressure areas to lower pressure areas, provided by the unequal heating of Earth’s surface. Since there is friction and the planet rotates, wind exists, controlled by the combination of the pressure gradient force, the Coriolis force, and friction and these forces are what generate horizontal pressure differences, thus wind.
When pressures are relatively low and high cyclones and anticyclones can be born which are responsible for immense wind speeds and precipitation. Depending on the positioning on either side of the hemisphere, the geostrophic wind and gradient wind implies that in the northern hemisphere a cyclone will circulate in an anti-clockwise formation and the anticyclone will spin in a clockwise formation. This is reversed in the southern hemisphere, cyclones will circulate clockwise, and anti-cyclones will circulate in an anti-clockwise fashion. When in the presence of friction the component of motion towards the lower pressure area produces the spiraling effect that strains from the centre. Upper level wind systems are thought of as consisting of uniform flow, rotational flow (cyclonic and anti-cyclonic curvature), convergent and divergent flow (where the horizontal area of air mass expands or shrinks) and deformation (the horizontal area of air mass remains constant). These wind systems located in the mid-latitudes usually obtain a large component of uniform flow from west to east and cyclonic and anti-cyclonic vortices create a succession of waves set at periodic intervals known as Rossby waves.
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