Weather and sky conditions are for a pilot like the oceans and waves for a sailor. Understanding the weather plays a big role in ensuring that the aircraft flies safely from A to B. Wind, temperature, air pressure, and visibility are important factors not only as fly the plane but also how punctuality and comfort will be your flight. affected.
Atmosphere
The atmosphere can be described as the mass of gas that rotates and moves around the earth without a definite limit. At this point, it is important to understand that the atmosphere is moving with the earth. Understand why later. It consists of about 78% nitrogen, 21% oxygen and 1% a mixture of other gases including carbon dioxide, hydrogen and argon. The air produced by these gases behaves very similarly to liquids.
The atmosphere is divided into five main layers but commercial aircraft fly in the lower two layers - the Troposphere, which is closest to the surface, and the Stratosphere, which is directly above it.
As it rises in the Troposphere, air pressure, temperature and air density all decrease. For every 1,000 feet it rises, the temperature drops to 35 ° F. This continues to about 36,000 feet, where it meets the Tropopause, which is the boundary layer before it reaches the Stratosphere. Here, the temperature stops decreasing with increasing altitude and becomes a constant value.
I would say ‘about’ 36,000 feet because the altitude of the Tropopause varies from day to day, season to season and most importantly, depending on its location in the world. Tropopause is influenced by the temperature of the air below it. The warmer the air, the higher the Tropopause. As a result, the tropopause tends to be lower above the poles (about 25,000 feet) and higher above the equator (about 55,000 feet). Tropopause is important because it acts effectively as a cover, keeping most of the weather under it.
Because such conditions can occur worldwide, for standardization, pilots use the International Standard Atmosphere (ISA). Under ISA conditions, at sea level airfield, the temperature is 59 ° F, drops to 35 ° F per 1,000 feet and the air pressure is 1013 hectoPascals (hPa). The pilot then referred to the condition on any given day as ISA +/- as many degrees.
So, now that we know the structure of the atmosphere, we can see how it affects the aircraft and how it affects your flight.
Wind
We are all aware of the influence that the wind has on us, but what exactly is it? Wind is defined as ‘continuous horizontal movement of air’ and is caused by changes in air pressure. When you watch the weather forecast on TV you see the wind measured in mph. However, in flight, it is measured in knots (kt) - 1kt = 1.15mph.
You've probably seen a table like the one below, which shows high and low pressure areas. Air naturally passes from a high pressure zone to a low pressure zone - like water flowing down and filling a low zone. This airflow is what we experience as a wind.
The circles on the graph are called isobars and show zones of equal pressure. The closer the isobars are, the greater the change in pressure for a given distance, and therefore the stronger the winds. We also know that, in the northern hemisphere, air moves counterclockwise around areas of low pressure and to the right around areas of high pressure. The opposite occurs in the Southern Hemisphere.
As a result, by looking at a table like the one above, you can find out which direction the wind is coming from and how strong the wind is. Knowing what the wind is doing is one of the most important factors pilots need to know for their flight.
Why is this important for pilots? First of all, let's dispel common myths. Contrary to popular belief, they are not the engines that make airplanes, they are wings. The engine only provides forward acceleration.
This is because the wings work by circulating the air on their surface. When the airflow reaches a certain speed, the wings begin to exert a lift. When the resulting lift is greater than its weight, the plane will rise into the air. The engines provide propulsion to create airflow across the wings. As a result, wind strength and direction (speed) are very important for an airplane at all stages of flight, especially during take-off and landing.
During takeoff, if the wing needs 100kt of airflow over it (airspeed) to create enough lift to fly, in zero wind conditions, the aircraft must accelerate to 100kt on the ground (groundgred) to leave. However, if there is a 20 knot wind blowing in the nose of the plane, the headwind will only accelerate to a moving speed of 80kt before it can take off. In fact, the plane started + 20kt before it started moving.
Conversely, if there is a wind blowing 20kt from behind the plane, the wind from behind starts with -20kt wind. As a result, it must accelerate to a travel speed of 120 kt before it gets enough lift to be carried through the air. This extra speed means the plane needs more runway before it reaches takeoff speed. As a result, you understand why pilots prefer to fly above the wind.
It's the same for landing. With a front wind speed of 20 knots, the aircraft can have an airspeed of 100 knots but only have a ground speed of 80kt. This would require a much shorter runway than if the aircraft had a rear wind of 20 knots and an resulting ground speed of 120 knots. Next time you're about to do a take-off run, look out the window for the windshield. You will see, more often than not, that you are pointing to a runway.
When the wind is really strong, the plane's landing speed can be very slow. While this is not a problem for pilots and aircraft, it does cause headaches for Air Traffic Control. As the plane moves on the ground more slowly, that means fewer landings every hour. This isn't a problem at small airports, but in places like London Heathrow, the effects can be very significant.
To minimize delays due to high winds, ATC uses a system called TBS - time-based separation.
If I tell you that turbulence is caused by elevator fluctuation, it should come as no surprise to you that turbulence is closely related to wind speed. When an airplane flies with an air mass moving over the earth (remember from the atmosphere above?), It is subject to ever changing wind speeds. This constant variation makes changes to the lift the wing provides at any given time. When the wind blows, the elevator goes up. When the wind descends, the elevator slows down.
Multiply this change hundreds of times every second and you will be angry. The greater the change in the elevator, the more bumpy it feels.
Low level wind
You may have noticed that on windy days the flight looks pretty smooth right up to the final landing stage and then it starts to dig. This is unfortunate - it has something to do with something called a 'boundary layer'.
Think about fast moving rivers and how water flows, remembering earlier that air behaves like a fluid. In the middle of the river, water flows beautifully and smoothly, not obstructed by anything. But on the edge, the water started to churn like it happened on the rocks and stuck to the shore. It's the same in the air.
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